Lonely Planets of the Cosmos

Hot Jupiters are special beasts in the exoplanetary menagerie. These giant worlds orbit their parent stars incredibly tightly, sometimes zipping around in barely a day or two, and so close that they can disturb the stellar atmosphere itself – as well as throwing themselves at the mercy of gravitational tides and scorching radiation.

They were also the very first type of exoplanets to be detected around normal, hydrogen-burning, stars like our Sun in 1995. This was both a great triumph of the ingenuity and perseverance of a few astronomers, and a great surprise. Up to this point it was almost an unwritten expectation that other planetary systems would in some way be like ours. Smaller rocky worlds would orbit closer to stars and gas and ice giants would orbit at a distance, mimicking the solar system, but also matching our relatively simple picture of how planets should form.

Hot Jupiters threw all of this for a loop. There was no way that they could have formed in-situ, suggesting immediately that some mechanism had moved them, or migrated them, into their toasty environments from an origin much further out. There are a number of possibilities for how this can happen. A massive proto-planet, more than 10 or 15 times the mass of the Earth, can set up density waves, or wakes, in the vast disks of gas and dust surrounding a proto-star. These spiral patterns of matter in turn exert a gravitational force on the planet, sometimes driving it inwards by bleeding off angular momentum. A young giant can quite rapidly burrow its way in close to a parent star this way. Another good possibility is that proto-planets form in configurations that are inherently unstable. Their gravitational pulls on each other eventually perturbing orbits to a point where planets collide, dive into the parent star, are ejected altogether to interstellar space, or are simply pushed into elliptical paths with small periastrons (closest approaches to the star) where gravitational tides collapse the orbits into the tight, nearly circular shapes that hot Jupiters inhabit.

What has remained somewhat unclear however is what any of these scenarios mean for other, smaller planets in these systems. Some computer simulations of planet formation have indicated that terrestrial-sized planets could perhaps survive the inwards migration of giant worlds in roughly 30% of cases, but other scenarios predict that to make a hot Jupiter a system must sacrifice many of its worlds.

Now a new study by Steffen et al. in the Proceedings of the National Academies uses data from the Kepler planet-finding mission to look for the signatures of smaller worlds around stars already proven to harbor giant hot Jupiters. In 63 systems the authors searched for signals of other transiting planets, or planets that might be perturbing the hot Jupiters – tweaking their orbital timing by their gravitational pulls.

The conclusion? Hot Jupiters with orbital periods of less than 3 days show no significant evidence for other planets (as small as 2/3rds to 5 times the mass of Earth) near to them. By contrast, ‘warm’ Jupiters on somewhat larger, though still small, orbits, and ‘hot Neptunes’ (lower mass giants) do show statistical evidence for neighboring worlds. This apparent isolation of hot Jupiters (although we don’t yet know for sure about even smaller mass planetary neighbors) indicates a very distinct pathway to their formation – planet on planet interactions that drive these worlds into elliptical orbits that then erode down to small sizes by tides. In this scenario very few, if any, hot Jupiter systems will ever harbor Earth-sized planets anywhere in the habitable zone. The situation for hot Neptunes, or hot Earths may however be different.

So hot Jupiters seem likely to spend their hellish lifetimes isolated from planetary sisters, the price paid for a very specific type of wild youth.

Tweets In Space (N. Stern and S. Kildall)

When the interplanetary missions Pioneer 10 and 11 launched in the late 1970s they each carried a metal plaque engraved with a set of pictorial messages from humanity. Eventually these extraordinary probes will traverse interstellar space, carrying these hopeful symbols towards anyone, or anything, that might one day find them. A few years later also saw the launch of the Voyager probes, this time carrying golden record platters filled with images and sounds of our homeworld and species. These were thoughtful and quietly speculative artifacts, cast to the stars for eternity.

Forty years later and our world has moved on considerably. We’re now a vastly more interconnected species, huge amounts of information flows around our planet on a daily basis, a torrent of articulate and inarticulate signals. We’re much more attuned to events as they occur anywhere on Earth, and much more likely to voice our opinion and to assume that our voice has a chance of being heard. It’s a tremendously interesting and exciting time, as well as an unsteady and often nerve-wracking one. And as this plays out we are also discovering that the universe is filled with other worlds, an enormous and terrifying number of planets around, and between, the stars. Some of these will almost certainly bear at least a passing resemblance to our own, perhaps never ‘Earth-like’, but conceivably ‘Earth-equivalent’, and we may have already found a few of them.

All of which makes a new art-meets-science project even more provocative and exciting. “Tweets In Space” is the creation of Nathaniel Stern and Scott Kildall and seeks to do nothing less than transmit a stream of your tweets towards one of the best current candidates for a planet capable of harboring life, the super-Earth GJ 667Cc – a roughly 5 Earth mass world orbiting an M-dwarf star only 22 light years away.

If all goes well then in September 2012 Tweets In Space will go live at the International Symposium on Electronic Art in New Mexico, and your Twitter account will become (as the creators suggest) your personal interstellar communications device. Tweets with the hashtag #tweetsinspace will be broadcast towards GJ 667Cc, as well as form part of an extraordinary live and web-available animated display (you really have to check out the video, below here). It’s tremendous fun, but it’s also a fascinating experiment. Stern and Kildall are no strangers to investigating the possibilities of human interaction and art brought about by the internet, their collaboration “Wikipedia Art” was a genuine phenomenon, making it to the hallowed pages of the Wall Street Journal, The Guardian, and The Huffington Post.

I asked them about the more technical aspects of the project – such as actually making an interstellar transmission, and they have an impressive technology road-map for trying to make this a reality (including making decisions about whether to send Tweets as digital data or as analog, pictorial representations, which is very clever). Right now they may have to build their own transmitter and so have a call out on the fund-raising site Rocket Hub to try to raise the approximately $8K needed to be confident that the Tweets have a chance of making it to GJ 667Cc. It’s also possible that an equipment option will be forthcoming from established commercial or federal organizations who can lend ‘big gun’ infrastructure to the transmission.

What I personally find very exciting about the whole concept is the unfiltered nature of it, and the fascinating mirror it will hold up to us all. We really are a different world from when the Pioneer and Voyager probes launched, and other deliberate radio transmissions to the stars have typically been sober and highly structured. The general radio noise we spew into the cosmos has also diminished as we’ve moved into the low-power digital age, so the well-worn adage of aliens coming across our dreadful TV shows may no longer be true. Is it safe to send thousands (millions!) of 140 character long missives to the stars? Older posts at Life, Unbounded have certainly considered the problems of interstellar memes (units of cultural information), but the bottom line is that we really have no idea.

So I think that anything which forces us to stop and consider what it is that we really feel represents humanity – good, bad, or indifferent, is an excellent opportunity. Tweets In Space is well worth our support – so go check it out, and consider helping build that transmitter! The icing on the cake is that Stern and Kildall will make all of their technical work open source, making one wonder how long it is before high-school kids forget about weather balloons carrying cameras to the upper atmosphere, and instead reach for the stars.

It’s quite astonishing, and brings this world and its satellites to life as if they were all part of a busy, busy little protozoa, floating its way through a vast and dark cosmic ocean. So enjoy “Outer Space”.

The Bug Nebula (NASA, ESA and A.Zijlstra (UMIST, Manchester, UK))

One of the most widely known and repeated astrophysical facts is that stars produce all the heavy elements that eventually make planets, shrubberies, and the likes of us. It’s absolutely true, but how exactly do they get those elements out into the universe to do all that?

A major route is stellar explosion. When supernovae go off they spew element-rich matter into the cosmos on a big scale, pushing it out for as much as a few hundred light years. But it’s not the only way for a star to dig into its pockets to hand out loose change. In fact, all moderately massive stars – from roughly solar mass to several times larger – can go through a phase after they’ve exhausted the fusion of hydrogen in their cores where they expel huge amounts of material. They do this by periodically inflating their outskirts, and then blowing this matter out to interstellar space. As much as half the mass of the star can be cast off this way. This freshly produced star-stuff consists of both gas and microscopic dust grains that are produced as the gas cools down away from the star and quite literally condenses out, forming silicate or carbon particles (the latter from lower mass stars). This hazy outflow dumps new elements into space to produce some beautiful structures, known rather confusingly as ‘planetary’ nebula.

The Cat's Eye Nebula - matter blown from a star (NASA, ESA, HEIC, and The Hubble Heritage Team (STScI/AURA))

The Ring Nebula (The Hubble Heritage Team (AURA/STScI/NASA))

The problem is that we haven’t fully understood how stars perform this trick. The only tool they have at their disposal is the pressure of stellar photons – light flooding from the star can push and accelerate material away from it. However, getting this light to push against the gas of the stellar atmosphere efficiently enough to set it in motion has seemed difficult. One option is that the tiny grains of dust act like miniature solar sails, that in turn snowplough through the gas to accelerate it along in front of them. However this theory has had some gaps in it; figuring out the necessary combination of dust grain composition, size, and location of formation has been tricky.

A new investigation recently published by Norris et al. in the journal Nature (and discussed in an excellent companion piece by Susanne Höfner) exploits some very clever astronomical observations of flatulent old stars to find a possible solution. By studying the polarized light from a number of these systems, and by using interferometric techniques, the authors were able to test the properties of dust that appears to be produced remarkably close to stellar surfaces, at barely a couple of stellar radii away.

The dust particles are surprisingly large, with diameters of about 600 nano-meters (0.0006 millimeters), and must be quite transparent to the stellar light or else they would be boiled away as they absorbed radiation. Yet this would seemingly make them poor solar sailors. The solution to this conundrum is that these are silicate grains (perhaps magnesium silicate) that scatter the starlight rather than absorb it, like rather rough mirrors. These ‘big’ grains can be readily pushed outwards at speeds of 20,000 miles an hour, and they will sweep up anything in their way.

Thus, the dispersal of elements into the cosmos may owe a lot to a most peculiar type of sandstorm, taking place in the messiness around dying stars. This remarkable process may be critically important to understand for cosmological reasons as well. Höfner points out that the more massive stars that go through this stage are also the likely progenitors of Type Ia supernovae, the explosions cosmologists use to track the changing expansion rate of the universe. Proper knowledge of the true, sandy environment of these vital yardsticks would be a very good thing.

It's a desert out there...(Image created from source material by: NASA, ESA and A.Zijlstra (UMIST, Manchester, UK) and Rosino (Wikipedia))

Planet, planet, planet.... (Image credit: ESA)

Exactly how many planets orbit any given star is still a major unknown in exoplanetary science. The two primary techniques for detecting planets and quantifying their characteristics have significant limitations that blinker us to the full contents of other solar systems. Radial velocity measurements pick up the tell-tale motion of a star around a system’s common center-of-mass, or balance point, due to the gravitational pull of any planets. But the smaller the planets and the further they are from the star the weaker the signal. Multiple planets and longer orbital periods confound the situation by producing complex patterns that may also be incompletely sampled in data that spans only a few years. Transit observations, such as those undertaken by the Kepler mission, are biased towards the detection of large planets in small orbits around small stars where it is most likely for a planet to block the light from the star more frequently.

Spot the planets - if you can. Time series data of the radial velocity of HD 10180 (Lovis et al. 2011)

All of this means that in essentially all currently known systems we may have only incomplete information about the true number of orbiting planets. Nonetheless, stars with multiple planet detections certainly crop up. Of the over 550 confirmed exoplanetary systems there are over 90 with more than one planet (a total of more than 760 worlds). Now a new study of radial velocity data from the HARPS instrument suggests that one of these systems, HD 10180, may harbor nine major planets – usurping our own solar system from the top of the pile of planetary richness.

In a recent paper Mikko Tuomi applies a sophisticated Bayesian (probabilistic) analysis technique to measurements taken over a period from 2003 to 2009. The star HD 10180 is a close solar-analog, about 6% more massive than the Sun and of similar composition it lies some 127 light years from us. Previous investigations of this data had suggested that there could be six or perhaps 7 planets in the system, Tuomi claims the presence of two more objects, albeit at relatively low statistical significance. The masses of these worlds ranges from more than about 1.3 times the mass of the Earth to more than 65 times the mass, and the orbits place all of them within the equivalent of Jupiter’s orbit in our solar system.

If further observations bear out this claim, it will make the HD 10180 system an extraordinarily busy place. Nine planets, ranging from possibly Earth-sized to Neptune-sized and larger, all crammed into this star’s inner realm. Previous studies of other systems have already suggested that planets are often ‘maximally packed‘ – if they can form they will and as close together as allowed by gravitational dynamics. In such cases, any reduction in orbital spacing between worlds or increase in their masses would make the system unstable. In the case of HD 10180, the computer simulations that will tell us if these 9 planet candidates can actually form a stable system over billions of years have yet to be run, but it looks promising.

All of which raises an even more interesting question. There is no obvious reason for these to be the only planets in the HD 10180 system. The fact that the outermost candidate appears to have a 6 year orbital period is a strong function of the limitations of the current set of measurements, and the packed nature of this system doesn’t exclude even more objects on larger orbits. In other words, there is no telling how many planets actually orbit further out around HD 10180. The total mass of the 9 candidates is at least 170 Earth masses, but this is just over half the mass of Jupiter, and even if it were double this, it suggests that the original proto-planetary disk that made these planets could have had plenty of additional material to make more (assuming some similarity to our own solar system).

Just as we’ve seen that the galaxy is rife with planets, making our own circumstances seem a little less special, it may be that our own planetary richness is also quite mediocre.

Caution! Do not cross this line... (NASA/ESA, G. Bacon STScI)

“What a deep voice you have,” said the little girl in surprise.
“The better to greet you with,” said the wolf.
“Goodness, what big eyes you have.”
“The better to see you with.”
“And what big hands you have!” exclaimed Little Red Riding Hood, stepping over to the bed.
“The better to hug you with,” said the wolf.
“What a big mouth you have,” the little girl murmured in a weak voice.
“The better to eat you with!” growled the wolf…

Stars and planets have what might be the most dysfunctional relationship in astrophysics. Planet-sized objects seem to form contemporaneously with stars, coalescing and coagulating out of the great disk-like platters of gas and dust that orbit increasingly massive and dense central proto-stellar objects. Angular momentum (the product of the distribution of mass with its velocity) is shed from these central blobs into the surrounding disk, helping the star gather and relax into its final state and pushing some disk material into further orbits. But some planets, especially the larger ones, seem to be hell bent on getting closer, not further, from their parent stars. During the early stages of proto-planetary evolution they can migrate inwards, pushing and pulling against the disk of matter to haul themselves into astonishingly close and unexpected orbits – helping create the population of ‘hot Jupiters‘ that we find around a few percent of all stars.

Other mechanisms can also bring planets swooping in perilously close to their parent stars. Planets’ gravitational pull on each other can destabilize a system, causing some worlds to be ejected to interstellar space (presumably forming the population of known ‘rogue’ planets), and others to either come crashing into the central star or to end up on highly elliptical orbits that skim near to the star at their closest approach. Extreme proximity to a star can both strip off planetary atmospheres and volatiles (perhaps transforming a perfectly good gas giant into a more paltry object) and give rise to strong tidal effects between planet and star. These tidal effects, much like here on Earth, can stretch and squeeze a planet and also evolve its orbit. An elliptical orbit can be eroded down to something circular, matching what we see in these close-orbiting planets. But in particularly close configurations a planet can raise tides on the star itself, and one consequence of that is the potential for the planet to spiral inwards over millions to tens of millions of years and end up being shredded and engulfed by the star.

It appears to be all love and hate between planets and their stellar parents. But although the above scenarios are plausible explanations for the configurations we see in exoplanetary systems, we don’t know for sure what happens. In particular we don’t know exactly how often a planet gets gobbled up by its star.

Come here my pretty... (NASA/GSFC/Reddy)

An intriguing new study by Metzger, Giannios, and Spiegel may shed some light on this question, literally. Their paper on ‘Optical and X-ray Transients from Planet-Star Mergers‘ investigates what the precise consequences are when a massive planet (a hot Jupiter) winds up being destroyed by a star. Exactly how this epic disaster plays out depends in part on the relative size and density of the planet itself. A high density world will plunge deep into the stellar atmosphere before being disrupted, but it will generate a great hot wake of matter that can emit a ‘burst’, or transient blip of extreme ultraviolet or X-ray radiation. A low density planet will tend to just be ‘siphoned’ off into the star well before it gets close enough for rapid disruption, being steadily and somewhat discretely consumed. Interestingly, intermediate density planets can be shredded into a great disk of material encircling the star. This rapidly spinning matter will heat up through frictional effects and power a bright flood of radiation that will persist for weeks or months.

Thus, when a star eats a planet it’s possible that we would see it quite clearly. In fact these events may be as bright as more standard stellar ‘novae’ – where a white dwarf ignites a shell of nuclear fusion around itself – but distinguished in flavor and certain physical details. So the big question is how often do we expect this kind of thing to happen? Metzger, Giannios, and Spiegel dig into this and come up with an estimate that a star somewhere in our galaxy may eat a hot Jupiter between once a year and once every ten years. That’s a bit of a challenge to find, the sky is a big place, but they also point out that if we monitored our nearby galactic neighbor Andromeda (M31) with optical and X-ray telescopes we’d stand a pretty good chance of spotting this type of astrophysical infanticide. Similarly, the latest generation of all-sky monitoring observatories have a good chance of catching this consumption happening in our own galaxy.

So make sure to watch the heavens, you might just catch a glimpse of a planet being wolfed down…

An alien world in the raw (see below)

Have you ever wondered what it would really be like for a person to journey to a truly distant and alien place; another planet, even another planetary system? What kind of things would we first see through our windows, or our cameras? What would our sensory experience be in such a distant realm? Would we sit back and admire glossy high-definition displays, or have to assimilate quick and grainy snapshots – the result of serendipitous astronomical cinéma-vérité as we swooped into a system? The Apollo astronauts arguably had only partial sightings and limited views of a true moonscape until the very moment they set foot on the lunar surface. Certainly those of us trapped back on Earth merely caught our first excited glimpses of live human lunar exploration through fuzzy video-feeds.

Modern lunar missions do much better, Japan’s orbiting Kaguya (SELENE) probe returned stunning HD video of the Moon’s surface. But this is a brightly lit, relatively nearby environment, and one that in spaceflight terms we’ve become pretty expert at. Further afield, in the bleakly dim reaches of the outer solar system, real-time video and pictures are increasingly challenging to obtain. Even closer to home, in places like the abyssal ocean depths, the small portals of thickened glass in a submersible can only offer a myopic and blinkered view of what’s going on, and presumably even James Cameron will have to watch his recorded high-fidelity footage to see the bigger picture.

While robotic exploration of our solar system returns a vast archive of imagery, most of what we see on the front pages of newspapers and magazines, or in our TV documentaries, is highly processed – stitched together, and decidedly glossy. These are the best renderings the data can provide, but as glorious and beautiful as many of them are, I think they have lost some of the immediacy, some of the grainy and shaky quality that can make them feel a little more real. So what does the raw footage actually look like? The Cassini mission to Saturn has accumulated a huge archive of imagery and data over the course of its 8 year stay in this distant system, where sunlight is 1/100th as bright as it is at the Earth. Raw pictures are made publicly available, but these uncorrected and uncalibrated shots seldom get aired in full. For the fun of it, and to test the notion that these images convey a different experience, here is a small collection with a particular subject – the 300 mile diameter ice-laden moon Enceladus. The very first image here is the only one that has been ‘cleaned up’, but I have then cropped it as a crafty film-maker might, to create a certain emphasis. All the other images are ‘as is’, raw files taken from the Cassini archives (NASA/JPL-Caltech/Space Science Institute).

Two moons seen against Saturn's bulk. To the left and below the plane of the rings is Mimas, to the right is Enceladus, a bright icy ball some 300 miles across.

Enceladus hoving into view, from the dark side (raw Cassini image)

Enceladus in foreground, rings behind. A rough, raw, image with noise and structure that is not real (Cassini raw image)

Swinging around, Enceladus against a backdrop of noise and what may be stars (Cassini raw image)

Closer in to Enceladus, its tortured icy surface becoming visible (Cassini raw image)

Swinging in over Enceladus (Cassini raw image)

The surface of Enceladus, uncorrected image artifacts create vertical stripes across the image (Cassini raw image)

The extraordinary ridges and crevasses in the ice of Enceladus, to the bottom it seems as if there is cleaner, brighter material revealed from below inside a great crack (Cassini raw image)

The horizon of Enceladus (Cassini raw image)

The water vapor plumes or geysers from Enceladus's southern regions, illuminated by sunlight (Cassini raw image)

For me, these unclean images with their poorly adjusted contrast have far greater immediacy than the centerfold spreads that we usually get to see – how about you?

An interstellar web? (Original image by B. Torrissen)

A speculative but intriguing discussion that sometimes crops up when talking to people engaged in exoplanetary science goes like this; let’s suppose that we find an unmistakably terrestrial style planet around a relatively nearby star (less than about 30 light years away), perhaps even around one of the Alpha Centauri members, a touch over four light-years distant. Let’s further suppose that – possibly with the James Webb Space Telescope, or a next-generation ground-based super ‘scope – we gather evidence for an atmosphere and even find big chemical clues that there could plausibly be a biosphere on this world. What do we do next?

There are somewhat mundane answers – build better instruments, get better statistics – that may be the most realistic, but there’s also that nagging thought that the next thing to do would be to find a way to study such a planet up close. If enough coffee has been consumed then it’s a matter of finding a handy Tony Stark, willing to sink hundreds of billions into a robotic interstellar probe, on a long-shot for glory (or perhaps call up his real life role model, Elon Musk of SpaceX). There’s a problem though, unless you intend a very long round trip, how do you get the information back? While we are now pretty good at picking up signals from distant spacecraft – even from Voyager 2 at over 100 AU from the Earth – getting data back from a few light years is going to be hugely difficult. The required transmitter power, as well as interstellar scintillation, is conceivably a major hurdle.

A solution, that has cropped up in various guises, even in the idea of von Neumann probes, and the interplanetary internet, is that you don’t just send one probe. Rather, you send a chain of probes – pearls on a string – capable of communicating between themselves even if not individually directly back to Earth. It would take a long time, but as the furthest end of the chain crept towards a target stellar system we’d have ongoing feedback, the continuous relay of data as we crept through interstellar space. It might be optimal to build the biggest receiver and transmitter at the outermost practical limits of our solar system – the equivalent of an internet ‘backbone’ – with a clear line back to Earth. So how many probes would you need to get to somewhere like Alpha Centauri?

This system is about 278,000 astronomical units (AU) away. If we optimistically think we could build probes capable of high-bandwidth to-and-fro communication over a few hundred AU then we’re talking about a thousand or more devices. This sounds awfully challenging, but remember that we (as some hypothetical sublimely patient species) might not expect Probe-1 to reach Alpha Centauri for a few tens of thousands of years. We only have to launch every ten years or so. Even if each probe cost 10 billion dollars (allowing for lowered cost after the first few models) that’s peanuts over this timescale. In the meantime we have an ever extending tendril out into interstellar space. Being an innovative species we would undoubtedly think of more and more wonderful things to add to the probes, increasing the scientific return.

Powering transmitters and receivers, as well as sizing their antennae or dishes, is still a problem. Given the timescale to reach the target star then even radioisotopes are going to peter out (fission reactors are a no-go, the fuel burns out too fast – but perhaps carrying along enriched uranium is an option, as one of the commentators on an earlier Life, Unbounded post discusses). I personally think that supplementing fissile material with chemical energy might actually be the best option; carry a store of naturally chilled redox components, mix them periodically and recharge the batteries when a power-boost is needed, the ultimate fuel-cell.

One way to increase the efficiency of communication is to use lasers instead of more conventional radio frequency transmitters. In 1994 Lesh, Ruggier, and Cessarone of the Jet Propulsion Laboratory wrote up an interesting study of this in which they concluded that conventional radio communication from the vicinity of Alpha Centauri 4 light years away, with mega-watt power requirements, could perhaps be replaced by modulated lasers with a 20 watt output power (see also this excellent piece by Paul Gilster at Centauri Dreams). The bandwidth is nothing exciting, about 10 bits per second (no Netflix streaming then), but hey folks, it’s from around another star. Clearly if one instead used the pearls-on-a-string spacecraft configuration, the average comm-link distance could be drastically reduced, and the bandwidth and ease of signal-lock could be greatly increased.

All over-caffeinated speculation? Perhaps, but if we ever get serious about stepping beyond, then making sure we don’t drop the signal is going to be a very real issue, and building the outermost limbs of our information-obsessed species’ internet may be the easiest way to bring the universe back to us.

This post is a reworking of an old Life, Unbounded piece from back in 2010. It seems like an appropriate followup to the previous post on Mass Effect and the Fermi Paradox, perhaps a glimmer of where we go next…

Who's been munching my galaxy?

Right now, all across the planet, millions of people are engaged in a struggle with enormous implications for the very nature of life itself. Making sophisticated tactical decisions and wrestling with chilling and complex moral puzzles, they are quite literally deciding the fate of our existence.

Or at least they are pretending to.

The video game Mass Effect has now reached its third and final installment; a huge planet-destroying, species-wrecking, epic finale to a story that takes humanity from its tentative steps into interstellar space to a critical role in a galactic, and even intergalactic saga. It’s awfully good, even without all the fantastic visual design or gameplay, at the heart is a rip-roaring plot and countless backstories that tie the experience into one of the most carefully and completely imagined sci-fi universes out there.

As a scientist, and someone who will sheepishly admit to a love of videogames (from countless hours spent as a teenager coding my own rather inferior efforts, to an occasional consumer’s dip into the lushness of what a multi-billion dollar industry can produce), the Mass Effect series is fascinating for a number of reasons. The first of which is the relentless attention to plausible background detail. Take for example the task of finding mineral resources in Mass Effect 2. Flying your ship to different star systems presents you with a bird’s eye view of the planets, each of which has a fleshed out description – be it inhabited, or more often, uninhabitable. These have been torn from the annals of the real exoplanets, gussied up a little, but still recognizable. There are hot Jupiters, and icy Neptune-like worlds. There are gassy planets, rocky planets, and watery planets of great diversity in age, history and elemental composition. It’s a surprisingly good representation of what we now think is really out there.

Galactic spread of life...maybe. (Taken from J. Schombert, U. Oregon)

But the biggest idea, the biggest piece of fiction-meets-genuine-scientific-hypothesis is the overarching story of Mass Effect. It directly addresses one of the great questions of astrobiology – is there intelligent life elsewhere in our galaxy, and if so, why haven’t we intersected with it yet? The first serious thinking about this problem seems to have arisen during a lunchtime chat in the 1940′s where the famous physicist Enrico Fermi (for whom the fundamental particle type ‘fermion’ is named) is supposed to have asked “Where is Everybody?” The essence of the Fermi Paradox is that since our galaxy is very old, perhaps 10 billion years old, unless intelligent life is almost impossibly rare it will have arisen ages before we came along. Such life will have had time to essentially span the Milky Way, even if spreading out at relatively slow sub-light speeds, it – or its artificial surrogates, machines – will have reached every nook and cranny. Thus we should have noticed it, or been noticed by it, unless we are truly the only example of intelligent life.

The Fermi Paradox comes with a ton of caveats and variants. It’s not hard to think of all manner of reasons why intelligent life might be teeming out there, but still not have met us – from self-destructive behavior to the realistic hurdles of interstellar travel. But to my mind Mass Effect has what is perhaps one of the most interesting, if not entertaining, solutions. This will spoil the story; you have been warned.

Without going into all the colorful details, the central premise is that a hugely advanced and ancient race of artificially intelligent machines ‘harvests’ all sentient, space-faring life in the Milky Way every 50,000 years. These machines otherwise lie dormant out in the depths of intergalactic space. They have constructed and positioned an ingenious web of technological devices (including the Mass Effect relays, providing rapid interstellar travel) and habitats within the Galaxy that effectively sieve through the rising civilizations, helping the successful flourish and multiply, ripening them up for eventual culling. The reason for this? Well, the plot is complex and somewhat ambiguous, but one thing that these machines do is use the genetic slurry of millions, billions of individuals from a species to create new versions of themselves.

It’s a grand ol’ piece of sci-fi opera, but it also provides a neat solution to the Fermi Paradox via a number of ideas: a) The most truly advanced interstellar species spends most of its time out of the Galaxy in hibernation. b) Purging all other sentient (space-faring) life every 50,000 years puts a stop to any great spreading across the Galaxy. c) Sentient, space-faring species are inevitably drawn into the technological lures and habitats left for them, and so are less inclined to explore.

These make it very unlikely that until a species is capable of at least proper interplanetary space travel (in the game humans have to reach Mars to become aware of what’s going on at all) it will have to conclude that the Galaxy is a lonely place.

Now, I’d hesitate at placing odds on whether this specific scenario is actually the likeliest solution to Fermi’s “Where is Everybody?”  The mere fact that it’s an invention in a game we play would make it the most supreme irony if this turned out to be true. Nonetheless, the idea does hit on a few themes that are perhaps not crazy. One is that a galaxy full of intelligent, technological species may not be hospitable, a fact that could severely limit or ‘localize’ the spread of anyone (check out an earlier post on “Bad Aliens, Meme Armor, and Intelligence in the Universe“). Another is that there might be phenomena that switch on every so often and either purge life from large areas of the Galaxy, or make interstellar travel impossible. These need not be artificial. For example, we live with a four-million solar-mass black hole at the center of the Milky Way that shows evidence for episodic outbursts of energy as it accretes matter. A moderately large outburst probably happened 300 years ago, a really big outburst may have happened 25,000 to 50,000 years ago – blowing vast ‘bubbles’ of energetic particles into space. Could such events have a deleterious effect on space-faring species? Perhaps.

Better be careful...

And of course it could be that the reason we haven’t noticed the galactic hustle and bustle going on around us is indeed because we haven’t stuck our heads far up enough from our parochial planetary burrow. Who knows what will happen when we eventually do.

Are you my mommy? (RNA Center, UCSC)

Well, perhaps your great-to-the-hundred-millionth-grandmother was.

Understanding the origins of life and the mechanics of the earliest beginnings of life is as important for the quest to unravel the Earth’s biological history as it is for the quest to seek out other life in the universe. We’re pretty confident that single-celled organisms – bacteria and archaea – were the first ‘creatures’ to slither around on this planet, but what happened before that is a matter of intense and often controversial debate.

One possibility for a precursor to these organisms was a world without DNA, but with the bare bone molecular pieces that would eventually result in the evolutionary move to DNA and its associated machinery. This idea was put forward by an influential paper in the journal Nature in 1986 by Walter Gilbert (winner of a Nobel in Chemistry), who fleshed out an idea by Carl Woese – who had earlier identified the Archaea as a distinct branch of life. This ancient biomolecular system was called the RNA-world, since it consists of ribonucleic acid sequences (RNA) but lacks the permanent storage mechanisms of deoxyribonucleic acids (DNA).

A key part of the RNA-world hypothesis is that in addition to carrying reproducible information in their sequences, RNA molecules can also perform the duties of enzymes in catalyzing reactions – sustaining a busy, self-replicating, evolving ecosystem. In this picture RNA evolves away until eventually items like proteins come onto the scene, at which point things can really gear up towards more complex and familiar life. It’s an appealing picture for the stepping-stones to life as we know it.

In modern organisms a very complex molecular structure called the ribosome is the critical machine that reads the information in a piece of messenger-RNA (that has spawned off the original DNA) and then assembles proteins according to this blueprint by snatching amino acids out of a cell’s environment and putting them together. Ribosomes are amazing, they’re also composed of a mix of large numbers of RNA molecules and protein molecules.

But there’s a possible catch to all this, and it relates to the idea of a protein-free RNA-world some 4 billion years ago. In a new, and provocative study by Harish and Caetano-Anollés in the open-access PLos One, an argument is made for the co-evolution of RNA and proteins as a more plausible way for something as intricate as the ribosome to arise. In the regular RNA-world hypothesis this is not how it happens, RNA is effectively exclusive until eventually proteins come along. However, the authors of this new work applied the tools of phylogenetics – the measurement of evolutionary distance or age between key molecular sequences and structures – to ‘date’ different parts of modern ribosomes. Intriguingly both the RNA and protein pieces of the ribosome seem to follow a similar span of evolution, suggesting that this fabulously complicated molecule was gradually aggregated in a world made of both proteins and RNA and that the proteins were already being made via some other mechanism involving RNA. Once ribosomes developed, protein-manufacture could really take off in new ways, but this may not have been their origin.

It’s certainly a fascinating idea, a ‘ribonucleoprotein-world’ hypothesis, although time will tell if it becomes accepted by evolutionary molecular biologists. It does also hint at the notion of a ribosome being one of the first results of what we might recognize as a symbiotic relationship. So, your grandmother may well have been a molecule, a ribosome in fact.

It's full of lenses...

When astronomers talk about methods for finding exoplanets the list is relatively short. There is the radial velocity, or ‘wobble’ technique, which senses the motion of a star around a common center-of-mass with its planets. There is the transit technique, employed with great success by NASA’s Kepler mission, and there are direct imaging and phase-photometry techniques – challenging observations that seek the light being actually emitted or reflected from a planet. And then there is gravitational microlensing, the chance magnification of the light from a distant star by the distortion in spacetime due to the mass of a foreground star and its planets – with distinctive ‘blips’ or cusps of brightness due to any worlds aligned close to the right place in the star’s lensing field.

Sketch of one case of gravitational microlensing involving a planet in the lens system (NASA, ESA, K. Sahu STScI)

This form of gravitational distortion of the pathway of photons is called ‘micro‘ because the typical arrangements and masses of stars results in tiny images; while the light of a background object may be greatly  magnified we can’t see its distorted image directly, its light merges with that of the ‘lens’ stars, mere thousandths of a second of arc from it. The gravitational effect of a planet around the lens star is effectively amplified when it is close enough to the zone of maximum magnification, the Einstein ring, but its effect is also only seen as an additional and  asymmetric boost in photons arriving at our telescopes.

But the key phrase here is ‘typical arrangements’. Given the rarity of alignments between two stars separated by great distances, caused by the endless motions of all objects within our galaxy’s gravity well, the majority of such events that we see occur between stars that are both very distant from us – perhaps more than halfway between here and the center of the Milky Way. At these enormous distances (many thousands of light years) we cannot measure the motion of a lens star (or its potential lensing victims) relative to others, and so have no idea when or if any given star will magnify the light of something aligned directly behind it. The situation is rather different however for much closer stars. Not only can we obtain their ‘proper motions‘ with careful high-precision astrometry, the zone around them that is optimal for magnifying a background object is that much bigger in angular diameter, it is ‘meso’ not micro.

Thus, gravitational mesolensing opens up a number of intriguing possibilities. First, as discussed in a triplet of wonderful recent papers by Lepine and Di Stefano, and Di Stefano, Matthews, and Lepine, it becomes possible to predict when a nearby lens star may move close enough to the position of a distant object to magnify it, and the larger lensing angle may cause a directly measurable shift in the apparent position of that background star as well as its brightness. If there are also planets around the lens star the predictability of the event may allow us to snag the early or late lensing signature of worlds on larger orbits that we might otherwise miss. The larger scale of the lensing angles also offers a unique probe of the effect of any close-in, very short orbital period planets. And the icing on the cake is that nearby stars are much more amenable to the detailed astronomical measurements necessary to estimate their true masses – the true strength of the lens.

Click here to see VB 10 move across the sky (NASA/JPL-Caltech/Palomar)

So can this be done? The authors point out a specific case; the object VB 10 is a low-mass star (perhaps a tenth the mass of the Sun) a mere 19 light years away. VB 10 ‘scoots’ across the sky at about 40 kilometers a second in transverse velocity, a miniscule but measurable angular shift per year (see the animation to the left here). Earlier Hubble Space Telescope images reveal something small and faint in its path – a distant background star headed for the lensing zone of VB 10 in late 2011/early 2012. Has VB 10 produced gravitational mesolensing? We’re awaiting the authors’ report on their efforts to observe any possible event. It’s not an optimal case, a nearby lens moving very fast doesn’t provide the best combination of factors, but it really is a pioneer in what might just become a new tool for hunting exoplanets – welcome to the fold gravitational mesolensing.

As it was, and as it is, an ocean on Earth (T. Fioreze)

If there is one thing our universe makes a lot of, it is water. This isn’t an immediately obvious property based solely on the universal inventory of stuff. Hydrogen utterly dominates normal matter throughout the cosmos, and despite some 13 billion years of stellar nuclear fusion only a small number of these primordial protons have actually been digested by stars. Of these, most have ended up in helium nuclei, the rest in a tiny, almost imperceptible trace of elemental perfume. Compared to the number of hydrogen nuclei in the present-day universe, just a few tenths of a percent of atomic nuclei are elements heavier than helium. The most abundant however is oxygen, clocking in at roughly one nucleus for every 1,500 hydrogen nuclei.

But things like planets, and us, are all about these wisps of nuclear pollutants. And in relative terms oxygen and hydrogen combine to make water in stunningly colossal quantities. Recent observations of the dust and gas rich disks of matter surrounding nascent stars – the material that will coagulate to make planets in these systems – have revealed just how prevalent water can be; thousands of Earth-oceans’ worth lurking in frigid vapor in these places. In our own solar system we are constantly reminded of the presence of this brand of ancient water, both in the salty pores of some types of meteorites, and in the spectacular tails of cometary bodies as they release their volatile molecules to the warming embrace of solar radiation.

Here on Terra-firma, water has been, and still is, a critical and central ingredient of both surface chemistry and the deep processes in our crusty lithosphere and mantle, including in the lubrication of tectonic movements. However, individual water molecules come and go, being split back out into their constituent oxygen and hydrogen atoms, and recombining or being produced from atoms that were formerly part of entirely different molecular species. A hydrogen and an oxygen that once belonged to one particular water molecule might find themselves recycled countless times and dispersed like unwanted orphans to the farthest reaches of the planet. Our terrestrial experience of water is really one of continual change.

But a recent discovery suggests that there can be circumstances on a planet like Earth where the components of specific water molecules can be preserved en masse in the most unexpected places for billions of years. Writing in Nature Geoscience, Shaw et al. report on a study of the composition of volcanic glasses produced in underwater eruptions a mile down in the ocean off Papua New Guinea. By studying the isotopic composition of the hydrogen nuclei (e.g. the deuterium content) and that of boron nuclei they found that this material has the fingerprint of ancient oceanic crustal plates in which the original water was forced into the crystalline rock structure and then ‘distilled’ by the heat and pressure, eliminating heavier istotopes. But these plates have been driven down (subducted) into the deep mantle of the Earth (at depths of hundreds of kilometers) for 200 million to a billion years, only now returning to the surface as the planet carries on its ancient routine of geophysical cycling.

So, perhaps you can’t make a cocktail out of billion-year-old seawater, but you can certainly make a very, very dry martini with the essence of water molecules that were once in an ocean that existed at the dawn of our multi-cellular ancestors. As transitory as a planetary environment can be, it is also surprisingly full of the echoes of the past.

A data transmission problem? (Wikipedia/BigRiz)

Although still awaiting full confirmation, a breaking news report in Science (and Nature, see below) indicates that the measurement of an apparently faster-than-light travel time for muon-neutrinos generated at CERN and detected at the Gran Sasso laboratory – which hit the world headlines back in September 2011 – may have been due to a problematic physical connection between a fiber-optic cable and an electronics card in a computer.

The rumor is that when this connection was tightened and the signal timing through the cable re-evaluated it matched precisely the 60 nano-second discrepancy that had been attributed to possible superluminal neutrino speeds. Since the cable fed data from a GPS unit used in timing the neutrino passage, this would be a critical problem. It is also possible that the GPS was providing incorrect timestamp information.

A more detailed report of the issues and the intentions of the OPERA collaboration are available at this Nature web site. And I quote here:

“The OPERA Collaboration, by continuing its campaign of verifications on the neutrino velocity measurement, has identified two issues that could significantly affect the reported result. The first one is linked to the oscillator used to produce the events time-stamps in between the GPS synchronizations. The second point is related to the connection of the optical fiber bringing the external GPS signal to the OPERA master clock.

These two issues can modify the neutrino time of flight in opposite directions. While continuing our investigations, in order to unambiguously quantify the effect on the observed result, the Collaboration is looking forward to performing a new measurement of the neutrino velocity as soon as a new bunched beam will be available in 2012. An extensive report on the above mentioned verifications and results will be shortly made available to the scientific committees and agencies.”

We will have to wait and see if this is corroborated, but it suggests that any hopes of having spotted neutrinos skipping the light fantastic may have indeed been wishful thinking. Such is the nature of complex and extremely tricky physics experiments, a dodgy bit of wiring, or a piece of electronics slightly outside its design tolerance can make all the difference.

Nomadic world seeks friendly home (NASA/JPL-Caltech)

The notion of what constitutes a typical planetary system has undergone some serious revision in the past twenty years. Our own solar system, once seen as a timeless and almost mechanical entity, is now known to be on the margins of chaos. Long term modeling of its dynamical evolution suggests that orbits of an inner world like Mercury may evolve over billions of years into something unstable, eventually unleashing a dramatic revision of other planetary orbits, including those of the Earth and Mars.

Exoplanetary systems show signs of even more dynamical rearrangement, from migrated giant planets to violent dynamical ‘cooling’, in which young worlds can be ejected wholeheartedly into interstellar space. These rogue worlds, or ‘nomads’ really do exist, gravitational microlensing surveys have picked up the tell-tale brightening of distant stars that can only be produced by a population of small dark planetary bodies drifting around in the Galaxy. There are twice as many of these Jupiter-sized or larger objects than there are normal stars in the Milky Way. That is an awful lot of planets alone in the dark.

A stellar birth cluster, NGC 3603 (NASA/Hubble Space Telescope)

Except they don’t necessarily stay alone. A rather intriguing new paper by Perets & Kouwenhoven investigates the likelihood that planets ejected into interstellar space by their parent systems (again, as part of planet-planet gravitational interactions during early stages of system formation) might be captured later on by other stars, meekly taking up a place at the edge of the orbital table in these systems. This process is helped by the fact that most, if not all, stars tend to form in associations or clusters. Our own Sun is now generally thought to have formed among numerous sister stars, now long dispersed by their dynamical to-ings and fro-ings, and by the effects of Galactic scale gravitational tides as everything is conveyed around the galactic center. Measurements of radioisotope remains in our system support this hypothesis, by indicating the past presence of massive stars that once exploded as supernovae in our near vicinity some 5 billion years ago.

Allowing for this type of transient stellar clustering Perets & Kouwenhoven calculate that the odds of ejected, nomadic, planets being captured into large, long orbits on the outskirts of entirely different star systems are actually moderately good. If a lot of planets are ejected from their original systems then re-capture probabilities can be as high as 3 to 5%, which may not sound like much, but if the stellar cluster has 1000 members that’s a decent number, and if we extrapolate to the Galaxy as a whole that would mean a lot of ‘re-purposed’ planets lurking around the outskirts of stars – including binaries and stars with their own pre-existing planetary systems.

This can help explain some of the current direct imaging detections of planet-scale bodies in extremely large orbits (100 astronomical units, and further, from the star), which are otherwise quite a challenge to account for in standard planet formation models. It also makes an intriguing prediction that nomadic planets can be captured by stellar remnants – like white dwarfs, and particularly black holes, whose high mass increases the odds of planet capture.

Given the relatively weak binding of these nomads to their adoptive stars it also seems possible (in my opinion) that some of them might even end up being ejected yet again, drifting through interstellar space, and then once more taking up with another system along the way – at least during early times while the stellar grouping is denser.

So we may need to further loosen our conceptual picture of stars and planets as isolated islands. Planet formation is messy; youthful (and old) planetary systems can be touched by chaos, and stars – even black holes – may captain the ultimate in leaky boats with an unpredictable and motley press-ganged crew.

A Falcon 9 launches the Dragon spacecraft - which orbited and then reentered the atmosphere to splashdown in the Pacific in December 2010 (SpaceX/Chris Thompson)

We live in interesting times. Just as NASA’s most recent budgetary rearrangements seemingly threaten the very core of solar system exploration, with cuts that might pull the agency out of its participation in exciting efforts with Europe on the ExoMars project, the private space industry appears to be on an accelerating course to more real flights, real missions, and real exploration.

Elon Musk, the driving force behind SpaceX, has expressed his clear intentions to not only get humans to Mars in the next 10-20 years, but to get lots of humans to Mars, perhaps 10,000, perhaps many more. Such hubris could seem a little silly coming from almost anybody else, but Musk is poised to turn the spaceflight business topsy-turvy, making the missteps of others appear positively comical. If SpaceX says it’s going to Mars, it means it. Musk’s stated long-term motivation is nothing less than to ensure the survival of the species, by making us a multi-planet race. Funnily enough I find myself agreeing with him on this point, but (as I’ll describe below) also very nervous about what happens during the process.

The objection that people typically make to his kind of announcement is pretty hackneyed, and it goes along the lines of “we have enough problems here on Earth without spending money and resources to go to other planets, think of all the things we could solve here first.” Well, yes, and no. This is part of a much bigger debate, but I think a couple of points are worth mentioning. First, it seems pretty clear at this stage in human history that no successful large society really solves its problems by forgoing activities that push technology, science, exploration and inquiry forward. There is simply far too much momentum and dynamic change in a large human collective to keep it in safe stasis. Like it or not, the problems of our overwhelming presence on this world (in numbers, thirst, and hunger) are very, very unlikely to be solved if we just divert all our resources to medicine, green energy, and good deeds. This is not to say that we shouldn’t be chasing those things, but rather than senselessly trashing exploration and basic science to shore up resources we should try to stop waging wars and try to halt truly dysfunctional economic practices when we spot them (phew, there, I said it).

In the grand experiment of evolution we have a remarkable opportunity to put members of our kind on other worlds. Even if, like Mars, these places are far from comfortable, they are really only another extreme environment, and we’ve become very, very good at coping with those. It may be that going interplanetary is ultimately too challenging, but we won’t really know until we try, and I think there is greater risk for the distant future of our species if we don’t make the attempt.

Cute, but do we want these on Mars? (National Park Service)

But there is a catch with a gung-ho approach, and it’s a basic one, with many precedents here on Earth. Take for example the case of the genus Rattus, the not-so-humble rat. Over the past few centuries the flourishing of European and Asian ocean travel and exploration has allowed stowaway rats (particularly the Black, Brown, and Norwegian varieties) to jump ashore on over 90% of the world’s islands and island chains. The consequences have been devastating for seabird populations, rats are hungry little buggers, and eggs and chicks are a veritable a la carte menu for rodents. Other native species also suffer as rats gobble up fruits and seeds, disrupting the entire food chain. Some thirty percent (about 100 species) of seabirds are now considered to be at risk of global extinction, and the prime culprit is accidental rat contamination on previously isolated land masses. Exactly what this is going to do to the global environment over the long term is unknown, the physical isolation of these places is still a buffer, but for people living in some of these places it profoundly alters their otherwise sustainable economies and livelihoods.

Earth’s recent history is littered with stories like this, and its deep past is undoubtedly also replete with ‘contamination events’ caused by either instinctively driven migration and exploration of species, or sheer random chance. There is however one critical difference when it comes to human-driven events, we may have selfish and intellectual reasons to want to intervene and prevent such things. A defining characteristic of our species is the ability to observe and learn. It has served us incredibly well in the ferocious and unforgiving torrent that is biological evolution, and we’ll need it if we want to carry on across the solar system.

From a planetary contamination point of view one of the dirtiest things you can place in a pristine environment is an organism like a human, replete with our 100 trillion cells of microbiome each of us is a walking bio-hazard. We breathe out, we excrete chemicals and waste, our skin is constantly shedding. It would be next to impossible to keep ourselves isolated from the martian environment – especially if there were 10,000 of us there. Obviously we don’t know how bad a thing this might actually be, Mars could be (and have forever been) utterly sterile, in which case we’d not precipitate normal ecological disaster. But we might still want to be very careful about what microbial populations we first unleash; although bacteria are smaller than rats, they’re many times more potent.

Perhaps a more likely scenario is that Mars is no stranger to contaminants (an argument I made in an earlier post), nonetheless it will never have seen the kind of complex filth we would bring with us. Purely selfishly we would want to be extremely cautious about what we set in motion on a new world, and scientifically we would be foolish to be anything but careful, since Mars could hold keys to understanding our origins.

It has often been said that one of the motivations for finding life elsewhere in the universe is to increase our sample size – which is currently one. Extinct or extant organisms on Mars, whether related to us already or not, would offer a vital clue to the origins of life in this little corner of the cosmos. It would be truly awful irony if the first thing we did in transcending our planet-bound evolutionary path was to destroy the very evidence that would tell us where were came from in the first place.

So, SpaceX, what you’re doing is wonderful and exciting, and potentially critical for our species, just please, please tread softly.

The future on Mars? (SpaceX)

Satellite composite showing location of Vostok within the Antarctic continent (NASA)

Two and a half miles beneath the surface of Antarctica’s central Eastern ice sheet is a body of water 160 miles by 30 miles across known as Lake Vostok, after the Vostok research station above it, built by the former Soviet Union in 1957 and now operated by Russia.

Even by Antarctic standards it’s a brutal place, with the dubious honor of holding the record for the lowest measured temperature anywhere on the planet, a mind-if-not-body numbing -129 F or -89 C. Performing any kind of mechanical or scientific work in this environment is an immense challenge.

For the past 14 years a hole has been gradually drilled down from this location into the ancient layers of ice. Each short summer season allowing for a little more progress. Hints that there could be a vast sub-surface body of water arose in the 1950′s and 60′s. Ground penetrating radar later confirmed these suggestions – and Lake Vostok, with 1,300 cubic miles liquid water, was revealed some 2.5 miles below the ice (although only 500 meters below planetary sea-level).

Radar image of Lake Vostok (Satellite imagery, NASA)

It quickly became clear that this was an environment sealed away from Earth’s surface, and although the water in the lake may itself be slowly changed out by the deep ice-dynamics of Antarctica, this process could take well over 10,000 years. It is also possible that hydrostatic sealing has kept the lake truly isolated for millions of years.

So what’s happening in Lake Vostok? We don’t know. Devoid of light but likely bursting with supersaturated oxygen and other gases, Vostok has long been speculated to be a potential habitat for unique ecosystems of extremophilic microbial life (and who knows what else). Despite the clear risks of contaminating what may be a pristine and fragile environment, Russian scientists have now, after more than a decade, drilled to the top of the lake (see this BBC news item for example, and this report in Nature). Water samples are now going to be extracted by lowering the pressure from the drill rig (and getting, we hope, all the nasty kerosene lubricant and anti-freeze out of the system), and then given full biological and chemical analysis.

It’s tremendously exciting just as it’s also tremendously worrying that we will have messed up yet another irreplaceable ecosystem. Forward contamination of planets, as I wrote about in my last post, can happen right here under our (frozen) noses. However, if we’re lucky then what we’ll learn about the lost world of Lake Vostok may provide scientific impetus to get ourselves to one of the extraordinary sub-surface oceans that exist elsewhere in our solar system, from the Jovian moons Europa and Ganymede, to the geyser-spouting mysteries of distant Enceladus. It’s possible that what’s happening at Vostok Station today is the beginning of our next chapter in the search for life in the universe.

And, an added postscript, an excellent diagram of the vertical/horizontal structure of the lake and its surroundings.

Bacterial aliens (NASA)

A funny thing happened recently on the way to Mars.

A few days after the successful launch of NASA’s behemoth Curiosity rover with its Mars Science Laboratory instruments on November 26th 2011, a somewhat muted piece of news came out admitting that the strict biological planetary protection rules had not been adhered to quite as everyone expected. What this meant in practical terms was that the rover’s drill bits were not sealed up for launch with quite the same protocols for sterility as everyone had expected. Thus there is an added possibility that alien invaders from Earth are heading for Mars.

The reasons for trying to keep Curiosity and all of its bits and pieces effectively free of any Earthly biological (microbial) contamination are twofold. First, you don’t want to get to Mars, start sniffing for interesting organic chemistry and end up detecting someones nasal microbiome, or some other bits of our rich and soupy broth of organisms. That really messes up one’s ability to find martian life, whether extinct or extant. The second reason is that we don’t want to forward contaminate Mars, unleashing our alien fauna on what might be a pristine or ecologically fragile world. Even the landing site of Curiosity has been chosen to avoid any obvious water-ice deposits within 3 feet of the surface, for fear of contaminating the Martian hydrological system.

The minor breach in protocol for Curiosity’s drills is unlikely to spell impending biological apocalypse for Mars, but it does raise some fascinating questions, including whether humans have already contaminated Mars, and whether Nature has beaten us to it by hundreds of millions of years anyway.

Consider for example the case of the Viking landers. In 1976 these two large, stationary, laboratories touched down with parachutes and retro-rockets on opposite sides of the northern hemisphere of Mars. It was well understood that terrestrial biological contamination was a major issue – not least because of the sensitive biological experiments to be undertaken – and the landers were put through sterilization procedures before launch. The problem was that in the 1970′s our understanding of the microbial world was different than it is today.

Stick it in the oven for 30 hours, then serve. Viking lander being prepped for heat sterilization (NASA)

The protocol for sterilizing the Viking landers before launch included baking them inside their aeroshells under dry pressure at about 230 F (110 C) for almost 2 days. But nearly forty years later we know that extremophilic organisms exist which, if present on the Viking hardware, could have potentially survived such conditions with nary a shrug. Indeed, a hardy organism like the single-celled archaea known as Strain 121, not only survives at temperatures of 121 Celsius (250 F, a typical medical autoclave setting) but reproduces in these conditions. It’s foodstuff? Well, Strain 121 metabolizes iron oxide for a living, producing magnetite as a byproduct. While we might not expect such organisms to be necessarily lurking in NASA’s clean rooms, the problem is also that what was thought to be clean in 1976 is not so today. More than 99% of microbial organisms are not readily culturable (think Petri dish), and it’s only with our recently innovative biomarker detection techniques, and metagenomics that we stand a chance of spotting the presence of these elusive, but pervasive, lifeforms.

There’s a pretty good chance therefore that the Viking probes carried some number of intact, viable microorganisms – especially of the extremophilic variety – from Earth to the surface of Mars. This is not particularly controversial, one need only read the National Academies of Science 2006 report on “Preventing the Forward Contamination of Mars” to see it clearly stated that tools such as heat sterilization of spacecraft had, at that time, been untested for the case of extremophilic life. So, how big a deal would it be if Viking unwittingly carried organisms like Strain 121, or “Conan the Bacterium”  (the infamous Deinococcus Radiodurans) or cold-loving and caustic-chemistry-loving critters? We don’t know. The martian surface is terribly unforgiving, even for battle-hardened Earth microbes, so any release could very well remain highly confined and short-lived.

Impact ejecta, or spall (NASA)

But before we go patting ourselves on the back, there is another route for biological alien invasion, one that has nothing to do with us, and which has been active for approximately 4 billion years. This is known as “impact transfer”, the ejection of material from a planetary surface during collisions with asteroids or comets, and its subsequent travel through space until (sometimes) falling into the gravity well of another planet or moon. The chain of events may go like this: a large (kilometer scale) asteroid hits the Earth’s continental surface at an oblique angle. During the moments of impact a “spall layer” of Earth’s crust can be accelerated to escape velocity, thrusting a mess of rocky particles and chunks up out of the atmosphere and into space. Although this material experiences severe g-forces and temperature fluctuations, experimental studies indicate that conditions would certainly allow for hardy microbial or microscopic hitchhikers to be carried aloft.

What happens next is a fascinating result of celestial mechanics. The range of velocities and trajectories of impact ejected material result in a multitude of pathways. Some of the spall will fall back to Earth promptly, some will fall back over weeks and months, some will enter orbital routes that carry it away for tens of thousands of years before it too returns to Earth (a pathway that could put terrestrial chemical and biological material into “cold storage” during an episode of apocalyptic destruction on the homeworld). Other chunks go much further, entering what can be thought of as a very slow and very inefficient orbital conveyor belt. Some of this material can traverse interplanetary space only to be swept into the gravity well of another world or moon, including that of Mars, where it can rain down onto the planetary surface.

Simulations of these impact ejecta “transfers” indicate that over billions of years collisions will have resulted in bits of Earth (as well as other solid bodies) being spread out across the solar system, even arriving at places as distant as Europa or Titan. In these cases the ‘hit rate’ is low, perhaps one in ten million bits of Earth ejecta might ever make it to Europa or Titan over a million years, a smaller number would make the journey significantly faster. For Earth-to-Mars transfers the rate can be much higher, one in every thousand chunks of material ejected in a single impact event will make it to Mars in every million year interval after that initial dispersal into space. So over time the flux of transferred material (adding up all impact events) can be very significant.

While the jury is definitely out on the survival rate of organisms carried along within ejected pieces of Earth’s upper layers (radiation damage, temperatures, and nutrient availability are all factors), there seems little doubt that the opportunity exists for viable critters to undergo planetary transfer, and at very least for biochemical components to make the trip largely intact.

So, it’s quite possible that we ought to revise our preconceptions about planetary contamination. Nature may have already done a good job at mixing things up in our solar system (whose orbital architecture seems well suited to the transfer of impact ejecta), and the issue is perhaps less of whether Terran bio-filth has been dumped on a place like Mars, but more of when it last happened.

In the bigger picture we’re left with the prospect of discovering whether our  biology has invaded other worlds or whether we are the results of biology from (for example) a wet and warm Mars 4 billion years ago, or whether both things have happened. The odds seem good; we may be aliens, we may also be interplanetary mongrels.

Southern aurora (aurora australis) composited with NASA imagery

As we’re in the midst of experiencing some particularly stormy solar weather it seems appropriate to make a quick post with some nifty auroral images and time-lapse movies (see below). It’s also fun to point out that the phenomenon of aurorae (or auroras) is truly universal. Caused when high-velocity particles like electrons and protons expelled by (for example) stellar activity crash into the upper reaches of planetary atmospheres, aurorae are one of the most beautiful manifestations of fundamental physics. These speedy particles can dump energy into the electrons bound into atoms of atmosphere – oxygen and nitrogen on Earth for example. As the electrons rid themselves of this energy in order to snuggle back up to their atomic nuclei they bleed photons – the photons that light up the skies.

The complexity of the illuminated structures is testament to the complexity of the flows of atmospheric electrical currents and particles within a planetary magnetic field, together with the tendrils of incoming particle streams from a star.

Hubble Space Telescope of UV light emitted by aurorae in upper atmosphere of Jupiter (J. Clarke, ESA/NASA)

Earth does it, Jupiter and Saturn do it, Neptune and Uranus have been caught at it, and even Mars does it. We also presume that many exoplanets must also do it – in fact auroral emission mechanisms (which can also produce radio frequencies) could offer a truly unique way to detect and study planets around other stars.

For now though we can simply marvel at a light show that has played out across billions of years in the skies of planet Earth.

From Earth (TESOPHOTOGRAPHY)

..and from space (the International Space Station/thesuntoday.com)

The planet Upsilon Andromedae b in close orbit to its parent star (NASA/JPL-Caltech)

Understanding the structure, dynamics, and chemistry of planetary atmospheres is key to exoplanetary science. It’s sobering to realize that as of now it is still an enormous challenge to model even the atmospheres of planets in our own solar system. Despite great advances, a variety of trickery has to be employed to simulate a swirling maelstrom like the Jovian atmosphere, pretending for example that it has a very different soupiness and energy transport in order to overcome computational demands. Modeling the atmospheres of gas giant exoplanets is even more in its infancy. Nonetheless, an intriguing result a couple of years ago came from Crossfield et al. and their study of how we see the infrared light varying in the planetary system of Upsilon Andromedae. Their Spitzer space telescope phase photometry (light seen as time passes) on Ups And reveals the glow emitted by the innermost, roughly Jupiter sized, planet around this F dwarf star (about 1.3 times the mass of the Sun).

The planet orbits very tightly, every 4.6 days, and is expected to have been evolved by tidal interaction with the star to a state of spin-orbit-synchronicity – in other words, in the simplest case, its day will equal its year and there will be permanent day/night sides. This sets the planet up for an extreme case of thermal disparity (about 1,400 Celsius in this case). We’d expect hot atmosphere from the day-side to flow to the cold night half of the planet – in doing so there might be great jet-stream like structures, and the hottest point of the planet might get shifted along in the direction of these winds. Something like this seems to be happening on Ups And b, but to an extent that is truly puzzling. As it zips around in its orbit, the glow of the hot atmosphere betrays that temperature distribution, in a fingerprint of infrared photons collected by Spitzer.

The misaligned hotspot of Ups And b (Credits in image)

In a nutshell – the hottest part of the atmosphere is not in synch with the planet orbit – or more specifically it is systematically offset or phase-shifted by almost 90 degrees. In other words, the hottest side of the planet is almost at right angles to the direction of the star. On the Earth this would be a bit like saying the hottest time of day is at sunset instead of noon.

It’s a puzzle. Some amount of offset might be expected, driven by the strongly blowing hot-to-cold winds, but this is extreme. There are various possible explanations – maybe the stellar heating is reaching to greater depths in the planetary atmosphere than expected and altering the fundamental dynamics. Perhaps the winds are so strong that they are going supersonic, forming great shock waves that pile energy up on this side of the planet. It’s a tough call – even theoretical models of these hot Jupiter-like planets disagree on such things, and none of them predict exactly what we see on Ups And b. The good thing about this result is that it challenges the modelers to really sort out what works and what doesn’t – advances will be made.

Crossfield et al. also end their paper with an interesting fact. This system of Ups And is actually too bright for the James Webb Space Telescope (JWST) to observe at shorter wavelengths – its sensitive instruments would simply be saturated with photons, blinded by the light. They further point out that a small space telescope dedicated to studying the phase curves of nearby hot-Jupiter systems might just provide the data needed to crack the problems of these extraordinary regimes of planetary atmospherics. This is a sentiment that could also apply to the hunt for terrestrial-type exoplanets – especially those that transit stars that are much closer to us than the distant Kepler objects. We need a dedicated all-sky survey to find the targets for powerhouse instruments like JWST, especially those that aren’t going to require planetary sunglasses.

(This post was adapted from an older post on Life, Unbounded in October 2010)

Earth-sized planets near and far (NASA/Ames/JPL-Caltech)

Planets in habitable zones, planets orbiting twin suns, miniature solar systems, rogue planets, planets, planets, planets. If there is one single piece of information you should take away from the recent flood of incredible exoplanetary discoveries it is this: Our universe makes planets with extraordinary efficiency – if planets can form somewhere, they will.

We’ve been sidling up on this fact for some time now, but it’s still a remarkable thing to acknowledge. Ten to fifteen years ago, as the first exoplanet detections began to come in, we understood that what we were seeing was potentially just the tip of the iceberg. These were massive objects (Jupiter sized or greater) and most of them were orbiting much closer to their parent stars than any equivalent giant planet in our solar system – hence the ‘hot Jupiter‘ moniker that is still used today. Statistics improved, as did our understanding of how detection techniques were biased towards finding these types of planets (owing to their greater gravitational influence on their parent stars), and estimates were made that suggested only a few percent of normal stars harbored such worlds.

Plot of exoplanet mass estimates versus year of discovery (generated from the online Extrasolar Planets Encyclopedia, thanks to Jean Schneider). The object shown in 1989 is known as HD 114762b, and is open to some debate in terms of actual discovery date and planetary classification as it may in fact be over 100 times the mass of Jupiter, nonethless it exists in this online compilation of exoplanetary data.

Of course time went by and astronomical instruments were refined, more and more data was accumulated, and longer orbital period planets and less massive planets were discovered. The figure to the left here illustrates the evolving range of planetary masses (or lower limits to planet masses) as a property of the year of discovery for confirmed exoplanets (excluding the thousands of to-be-confirmed-candidates from NASA’s Kepler mission). Here in 2012 we’re dipping well and truly into Earth-sized planetary terrain (about 0.003 times the mass of Jupiter on this scale).

By 2010 gravitational microlensing searches for planets were indicating that Neptune-sized objects on large orbits were at least 3 times more common that Jupiter-sized planets at similar distances from their parent stars. And hot on the heels of these measurements new Doppler, or ‘wobble’, detections of exoplanets indicated that at least 1-in-4 normal stars should harbor Earth-sized planets within about a quarter of the distance of the Earth from the Sun (0.25 AU).

It was becoming increasingly apparent that planets might be plentiful. Entering 2011 then the first big results from NASA’s Kepler mission began to make waves. With these came the statistical inference that the most numerous types of planets orbiting within 1/2 an Earth-Sun distance (0.5 AU) were Neptune-sized worlds, clocking in with a frequency of occurrence of about 17% (i.e. around 1 in every 6 stars). Close behind came Earth-sized objects, in about 6% of all systems. With a little extrapolation, and assuming a total of 200 billion normal stars in the Milky Way galaxy, it was clear that there might be millions of Earth-sized worlds in the habitable zones of their stellar parents, across the galaxy.

But things were just starting to warm up. The next item was another statistical inference from gravitational microlensing surveys, that now indicated a very substantial population of ‘rogue’ planets – giant worlds perhaps ejected from their stellar nests by strong gravitational interactions with other planetary chicks. The conclusion was that free-floating, wandering, objects as large, or larger than Jupiter, outnumbered stars in our galaxy by almost 2 to 1. It’s a remarkable result, but what about planets very much in the grasp of their parent stars, the equivalent of our own solar system?

Recently a new microlensing analysis by Cassan et al. appeared in Nature that explicitly targets planets orbiting between about 0.5 and 10 AU from their parent stars. The results solidify and carry forward all the measurements from before. About 17% of stars (give or take several percent) harbor Jupiter mass planets, cool Neptunes exist around about 52% of stars and Super-Earths (5 to 10 times the mass of Earth) exist around roughly 62% of stars. Even with sizable errors in these estimates (as much as 20-30%) the numbers are astonishing – there are at least 1.6 planets orbiting from 0.5 to 10 AU for every star in the galaxy. Combine this with the Doppler survey numbers (25% of stars with ‘Earth-sized’ planets within 0.25 AU), the Kepler numbers (17% of stars with ‘Neptunes’ orbiting within 0.5AU), and the microlensing estimates of 2 rogue giant planets per star in the galaxy and you have, well you have an awful lot of planets.

Of course one has to be careful in pulling these numbers together. Different detection methods and surveys have different biases, and if (for example) a giant planet orbits at 0.5 AU from its star then dynamical stability may preclude the possibility of other worlds nearby. Nonetheless, the bottom line is, I think, very clear; there really are planets everywhere, and they must number in the hundreds of billions in the Milky Way.

The results of glorious chemical and energy flux on a planet (L. Topinka, USGS)

Despite where we find ourselves, on a small rocky world, there was no reason to believe that the universe would make planets as efficiently as it seems to. Our situation is merely one data point, and a horribly biased a posteori one at that, and our models of planet formation are, to be quite frank, struggling to keep up with the flood of new data. Nonetheless, from the point of view of astrobiology and the search for life elsewhere, planetary bodies remain the primary, critical, target. There are simply no other environments in the cosmos that offer the same potential for diverse and complex chemistry in multiple phases of matter, and the potential for such long-term equilibrium (albeit a dynamic type of equilibrium with energy and chemistry in both sporadic and cyclical flux).

Thus, the sheer abundance of planets profoundly impacts the nature of our exploration of the universe and our quest to understand our own significance or insignificance. There is nothing trivial about the discovery of planetary plentitude, because it means that we are finally on the cusp of seeing whether a statement made two and a half thousand years ago is correct or not:

“To consider the Earth as the only populated world in infinite space is as absurd as to assert that in an entire field of millet, only one grain will grow”

- Metrodorus of Chios (Fourth Century B.C.)

It’s extraordinary to think how far we have come since these words were written.

(Oh, and as for moons, well don’t even begin to go there. Our solar system carries over 160 natural satellites around with it, so moons might yet turn out to be the most numerous planetary-type bodies of all…)

A black hole lenses the light of the Milky Way in the background (Credit: Ute Kraus amd Axel Mellinger)

This weekend Stephen Hawking turns 70, an extraordinary physical accomplishment to add to an extraordinary list of physics accomplishments. Seeing this news reminded me of the the first time that I crossed paths with Hawking. I’d love to be able to say that it was in intellectual debate, an exchange of brilliant ideas, but in truth it was excruciatingly awkward – at least it was for me.

Twenty years ago I was a fledgling scientist, a graduate student in astronomy at the University of Cambridge. One of the few general expectations of us was that we would occasionally have to prepare lunch for the Wednesday seminar at the Institute of Astronomy (yes, I know, it sounds positively Dickensian). Not only did this involve having to set out tables laden with bread and cheese, pate, fruit and vegetables, but it also meant that someone had to be sent to Cambridge market to buy the ingredients. On this particularly chill autumn morning that lucky person was me.

As I locked up my bicycle by the market square in central Cambridge I realized that I had no money and needed to pay a visit to the ATM (cash machine for the natives). It was early enough that the city was extremely quiet, only a few bedraggled figures coming and going, the Sun just creeping above the rooftops to yellow the sandy bricks. In a fatigued and blinkered state I made a beeline for my bank. Out of the corner of my eye I noticed a figure with an enormous red pram also clearly heading for the lone ATM on the side of the building, and I indecorously sped up to beat them to it. Except the enormous pram wasn’t a pram at all, and with a whirr it suddenly zipped past me to wedge itself in front of the bank, claiming the spot for the assistant trotting along after it.

Good grief, what a rude swine, I thought, and began making those English harrumphing, throat-clearing, tut-tutting noises that we use to express our complex and justified indignation. Of course that’s when I realized that it was Stephen Hawking who had just muscled his way to the ATM ahead of me. As I stood rather deflated behind him and his assistant, I couldn’t help but stare at this remarkable individual, whose Brief History of Time, a few years earlier had propelled him into the public eye.

Hawking’s accomplishments go far deeper than popularizing science. His contributions include work on a number of so-called singularity theorems (exploring the very nature of regimes associated with phenomena such as black holes, where geodesic incompleteness is manifest), the black-hole “no hair” theorem (black holes are completely described by only 3 properties – mass, angular momentum, and electrical charge, and are otherwise hairless), the emission of thermal radiation from black holes (typically known as Hawking radiation, the idea that a black holes have temperature and entropy, and can actually evaporate), the no-boundary picture of the Big Bang (removing the singularity at the very beginning of the universe), and the idea of the “top-down” cosmology (an appallingly clever and disconcerting idea that the present state of the universe is what determines its past, thus side-stepping various issues of fine-tuning the cosmos for the physical laws that we observe today).

The list goes on, and also includes contributions to many other fundamental cosmological questions, such as the origin of the tiny perturbations in matter that eventually gave rise to all the structures that we see today, grown by gravity. More recently Hawking has commented a number of times on the possible nature of life elsewhere in the universe, and the reasons why we should perhaps think about this in very practical terms. To quote him “If aliens visit us, the outcome would be much as when Columbus landed in America, which didn’t turn out well for the Native Americans.” (something that triggered one of my previous posts on “Bad Aliens“).

Suffice to say, many years later when I found myself sitting a couple chairs away from Hawking at a cosmology conference in Chicago, peeking at him painstakingly assembling a response to a question on his computer screen (it took 5-10 minutes to create a two sentence reply), I could barely face my shame at having ever been churlish enough to try to deny him first place in the ATM queue in a cold street one autumn morning.

Happy birthday Stephen Hawking, CH, CBE!

In my winter funk, I find myself thinking that this must be what it would feel like to be among the outer planets, frigid and dimly lit by a distant Sun, where our senses would register little difference between winter and summer. Perhaps the most stunningly austere is Saturn. Despite its vast ring system and 62 moons, this giant world appears in visible light as a smooth and positively minimalist sculpture, emotionally cold and distant. However it is also extraordinarily beautiful. So, as a last thought before our Gregorian new year, here are some examples of Saturn’s aloof majesty.

Saturn just past its equinox, imaged by the Cassini mission from a distance of 526,000 miles.

A giant and its brood. Titan seen above Saturn's rings, tiny Prometheus, Janus, and Mimas lurking closer to the equator. Giant shadows cast by the rings onto Saturn's upper atmosphere (NASA/JPL)

A tiny moon (Epimetheus, 72 miles across) is a little dim speck towards the center of the frame, vast Saturn looming over it (NASA/JPL/Cassini))

The haze enshrouded and frigid moon Titan, almost eclipsing icy Dione (itself the 3rd largest moon around Saturn) in the background. The shadows of Saturn's rings (seen horizontally across this image) play onto its atmosphere (NASA/JPL)

Some of Saturn's moons orbit close enough to the plane of the rings to cast long shadows at the time of equinox. In this case the culprit is Mimas, creating what looks like a tear in the fabric of space itself (NASA/JPL).

Uplit by the Sun and more generally by reflected sunlight from Saturn, the two moons Tethys (left) and Enceladus (right) appear to pass by each other. In reality Tethys is 162,000 miles further from Enceladus in this snapshot. Below Enceladus is a plume of water vapor being expelled hundreds of miles into space from its "cryo-geysers", a signature of what may be liquid water reservoirs beneath its ice crust.

Magnificent Saturn, subtle blue and gold tones, while its moon Dione circles in silence (NASA/JPL). The Sun's radiation is 100 times fainter out here than at the Earth, and Saturn's upper atmosphere can be as cold as -280 F.

The Sun rising above the Arctic plain (H. D. Nygren, NOAA Corps.)

As our spinning globe of rock and metal tracks its steady path around the Sun, we find ourselves crossing once again through the winter solstice, the point at which Earth’s northern pole is pointed as far from our fierce stellar parent as it can be (this year at a coordinated universal time of 5.30 am on December the 22nd, almost the same as 5.30 am Greenwich Mean Time). The chill that this brings to the northern hemisphere can make it seem a little confusing that a mere 12 days later, on January 3rd, the Earth also passes through its closest approach to the Sun (its periapsis point).

Why do we not get hot and bothered by this passage? The answer is that the Earth’s orbit is very close to circular, and so periapsis is only about 3% closer to the Sun than the furthest point in our great elliptical orbital loop. The resulting increase in solar radiation (a few percent) does toast the planet a little more, but locally it’s a small effect compared to that of our planetary tilt. Thus, for those of us in the north our closest passage to a star is still a bone-chilling affair.

Elsewhere in the universe this is definitely not always the case. So, while you’re sipping hot cocoa, or flinging innocent antipodean crustaceans on the barbeque, spare a thought for a planet less fortunate than your own.

HD 80606b: a serious case of repeat sunburn

Comparison of HD 80606b's orbit and the sedate architecture of our solar system (Credit: Greg Laughlin)

A mere 190 light years away, in the direction of the Big Dipper is a gas-giant world, some four times the mass of Jupiter. Every 55.5 days this planet switches between a moderate, temperate, distance from its ordinary, Sun-like, parent star to a ridiculously scorching place that receives more than 800 times as much stellar radiation. Welcome to HD 80606b, a planet with an orbital eccentricity of 0.93 and a closest approach to its star that is a mere 1/29th of its furthest distance – a startlingly near pass of only seven times the radius of the star.

As a result, HD 80606b experiences a rise in its outer atmospheric temperature of over 700 degrees Celsius in the space of 6 hours as it rockets through its periapsis with the star. We know this because, in a stroke of statistical luck, HD 80606b both transits its stellar parent (passing directly between us and the stellar disk) and is later eclipsed by the star immediately after its closest approach. The latter event allowing astronomers to catch a glimpse of the infrared radiation pouring off the planet as it dips its toes into the realm of Hades.

Subjecting a planet to this kind of brutal heating likely results in some spectacular atmospheric changes, with great hotspots driving colossal winds. Hydrodynamical simulations give us some idea of what might be going on.

Visualization of HD 80606b before, during, and after periapsis (NASA/JPL-Caltech/G. Laughlin et al.)

This movie shows HD 80606b from our Earthbound point of view. At first the planet has not yet passed through its periapsis, the blue color is light from the star reflected towards us. Four seconds into the animation is the closest approach, and now the red glow is the infrared radiation emitted from the planet itself – the equivalent of a peal of thermal thunder. As time passes, all we can see is the night side of the planet as it again climbs away from the star, but its atmosphere is still hot, roiling, and flowing from the massive radiation punch of its close encounter.

In this case nature has provided us with a wonderful experimental apparatus for understanding the effect of extreme variations of stellar radiation on a planetary atmosphere. Every 111 days (55.5 days out, 55.5 days back) HD 80606b goes through the same brutal experience, providing another opportunity for us to observe and refine our models.

While this is a truly extraordinary system, we expect that many of the “Earth-like” worlds on the cusp of being discovered, will have orbits that are significantly more elliptical than that of our homeworld. Our tentative investigations of what this would imply for life on such planets (for example, work by Dressing, Spiegel, Menou, Raymond and myself) yield some surprising answers. Quite strongly elliptical orbits (although much less so than HD 80606b) need not render an Earth-like, rocky, wet, world uninhabitable. While certain locations on such planets might indeed become uncomfortably hot or cold during the course of a year, the so-called thermal-inertia (the reticence of land or ocean to give up or absorb heat quickly) may carry these worlds through the worst times – smoothing out the extremes.

So, as we pass through our rather mild solstice and periapsis, there may well be another place, out there somewhere, bracing itself for its most appalling season, with only the comfort of the thought that better days are on the way.

A strange chemical reaction

Imagine, if you will, a planet with atmosphere, oceans, rocks and life. On this planet, most chemical reactions are either slow and geophysical, or quick and biological but very localized. There is, however, an exception. Because of the particular nature of this world there is the ever-present potential for a type of chemical reaction that is not only fierce and destructive, but also self-propagating. Once triggered it can spread across hundreds, even thousands, of square miles. It preferentially attacks and transforms living material – leaving behind a fragile deposit, stripped of most biomatter. It can only stop by either exhausting the supply of fresh reactants, or when its chemical energy is sucked away by an un-reactive medium.

This is a tricky planet. It forever teeters on the edge of letting this chemical storm get a grip, but its climate and varied topography helps to confine outbreaks. The very compounds responsible are themselves critical ingredients for much of the life on this world, and cannot be eliminated. Indeed, the reaction itself serves a number of key roles in stabilizing populations, cycling elements between air, ground, and oceans, and is ancient enough to have been incorporated into the survival strategies of large numbers of species.

Imagine we could visit this world. Entering orbit we would scan it with our telescopes. Curiously, at any given time, we would observe tens of thousands of these intense chemical maelstroms dotted across the globe. Their signatures would be quite distinct, and we might be quite astonished that life existed in such a perilous environment.

Of course, this is no hypothetical planet, it is the Earth. The chemical reaction we know as fire is a strange and intriguing, and often overlooked aspect of life here. The young Earth of 3 billion years ago, with little or no oxygen in its atmosphere, or much flammable biomatter, would have probably only seen fire in volcanic settings. Somewhere along the line, maybe a billion or two years later, with enough free oxygen, perhaps some dried up mat of plant life on a tidal shore was the first victim of arson – possibly a result of lightning. Today, fires cover the globe. Satellite imagery, or remote sensing, tells the story. The image at the top of this post shows thousands of fires scattered across south-central Africa, seen by the MODIS instrument on NASA’s Aqua satellite. Many of these have been set by humans, following an ancient pattern of land-use. Humans have learnt to exploit this chemical fragility.

Fires across Africa (in red) observed by MODIS on July 2011 (NASA). Click on image to go see the movie of a decade of global fires.

NASA recently compiled 10 years of MODIS data to produce an extraordinary movie of the Earth on fire. You can click on this image to the left (or here) to to go and view it.

I think we tend to underestimate the chemical reactivity of our homeworld. Fire is an excellent example – it’s so familiar to us that we (well, I) even have to pause to remember that it’s something chemical, fiercely exothermic. It raises a number of interesting questions. Is a phenomenon like fire simply a consequence of the kind of chemical reactivity needed for a planet to harbor life? Life on Earth needs a lot of reduction-oxidation pathways. Can you propel a biosphere to the kind of richness we see today without taking this walk on the wild side – risking destruction for the chance to make hay with oxygen?

Evidence suggests that, for example, around 270 million years ago atmospheric oxygen levels were significantly higher than today – and that fire was much more frequent on a global scale. More oxygen and it becomes hard to avoid burning all flammable materials, clearly there could be a feedback mechanism at play – complicated by geography and climate. Just how fire-prone can a planet become before it wipes out its surface biosphere? And that also raises another interesting question, could oxygen producing marine organisms wage fiery war on their land-living counterparts (either for some advantage in resources, or inadvertently), while safely contained in their wet and fire resistant habitat?

As our telescopes reach out across the galaxy in search of “Earth-like” planets, perhaps we should consider looking for the signs of not just idyllic biospheres, but also those where such chemical imbalances are, at least temporarily, making a mess.

Anyone got any marshmallows?

This post is adapted (and updated) from the Life, Unbounded archives.

Warning: Exoplanets may appear less massive than they really are (images used: Eysteinn Guðni Guðnason and NASA/Kepler)

Exoplanets can be confusing things. Recently we’ve seem the announcement of a milestone for NASA’s Kepler mission with the confirmation of a planet in the habitable zone of its Sun-like star. The planet, Kepler 22-b, has a diameter 2.4 times that of the Earth, which in exoplanet parlance puts it somewhere roughly in the “super-Earth” category. Hence the excited headlines about an “Earth-like” planet.

The truth is though, a planet of this size is almost without a doubt significantly more massive than the Earth, a fact pointed out by numerous pundits. So why don’t we know its mass for sure? The problem is that the technique used by Kepler to find planets simply measures the amount of light that a planet blocks when (by chance geometry) it passes between its parent star and our viewpoint. This yields the radius, or diameter, of a planet – not its mass. To estimate a planet’s mass the best bet is to try and measure the “wobble” induced on the star due to the gravitational pull of the planet. Alternatively, one can look for the variations in when the transit of other planets in the system occur (if they’re detected) – which also betrays information about these planetary masses tugging at each other. It’s also possible, again if there are multiple planets detected in a system, to try to deduce what the planetary masses really are by simulating the orbital dynamics to find what’s necessary for the whole system to be stable.

But for a single detection of a distant world like that of Kepler 22-b, for the time being we’re left with trying to guess what mass it might actually be. These guesses are however are based on some pretty sophisticated reasoning, and the key terminology here is “planetary mass-radius relationship”. In the simplest terms, suppose we knew what compounds a planet was made of – for the sake of argument let’s say it was made entirely of carbon. We could then apply our knowledge of the physics of carbon (in solid forms) to calculate how the gravity of all that carbon squeezes itself into a planetary ball, and what the radius of that ball might be for different masses of carbon. We know that carbon is somewhat compressible, especially if you stick a planet’s worth of mass on top of it, so we have to take that compressibility into account. We do this through what’s called an equation-of-state, precisely the same type of formula that tells you how much air you have to put into a tire to reach a certain pressure, depending on how hot or cold things are.

Doing this for real planets is, not surprisingly, a wee bit more complicated. Matter under pressure behaves in a variety of ways, the phases of compounds can change (e.g. like liquid turning to solid and vice-versa), and planets are likely to be multi-layered. We also don’t actually know what the composition of exoplanets really is, although we can make some pretty good educated guesses to get us started. Bearing all of these things in mind, astronomers and planetary scientists have invested a lot of effort into computing how it might all play out, and so we can begin to make some educated guesses at what the possible masses are for planets like Kepler 22-b.

And here’s an example of how planetary mass varies with planetary radius, in this case drawing on work by Fortney, Marley, and Barnes in 2007, also Gillion et al. in 2007. It’s not definitive, because of the inherent uncertainties in the physics, and other excellent studies such as those by Seager et al. will give slightly different answers. But it’s enough to get an idea of where Kepler 22-b lands.

The radius of planets versus their mass, for a range of possible compositions - from iron, to "rock", to ice, to large atmospheres of hydrogen and helium. The red dotted line shows Kepler 22-b's 2.4 Earth radius (Image adapted from C. Scharf, Extrasolar Planets and Astrobiology, University Science Books, with sources given in post).

…and it’s not entirely pretty. In fact, even if Kepler 22-b were made entirely of pure water ice, it would weigh in at about 5 times the mass of the Earth. Allowing for a more probable mix of ice and rock, and we’re up into over 10 Earth mass territory. If it had a similar composition to the Earth, then we’re looking at a world in excess of about 40 Earth masses – at which point all the “Earth-like” newspaper headlines should be consumed by fire.

Kepler 22-b is still a terrific result for Kepler, but the next time you look in your wing mirror just remember, objects may really be more massive than they appear.