Imagine we could voyage back in time, back nearly a third of the way to the big bang itself, back to when life on Earth was just emerging.
The exact details of how chemistry gave way to biology—of how life arose and took hold of our world—are now lost to the ages, swept away by more than four billion years of our ever changing planet’s history. What is clear, however, is that the secrets of life’s earthly genesis would be invaluable guides in the search for life elsewhere in the universe. And most fortunately, we have what amounts to a planet-scale time machine and origins-of-life chemistry lab within our reach.
Out past Mars and Jupiter, far off in the frigid depths of our solar system, is Titan, the largest moon of Saturn. This alien world is the only other planetary body around the sun with a dense atmosphere that is rich in nitrogen and carbon like our own. The uncanny similarities do not end with Titan’s air. Windblown dunes writhe over its surface; mountains, hills and canyons splay across the landscape. Rain falls from the skies, forming meandering rivers and streams that feed lakes and seas. There, organic compounds can undergo complex chemical reactions to form what may, in many respects, resemble the “primordial soup” from which life on Earth first sprang. Wisps of vapor rise from the land back to the sky to make new clouds and fresh showers, forming a cycle that mirrors that of Earth’s.
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Even so, this moon remains quite alien. Titan’s “waterways” are composed of hydrocarbons—liquid methane and ethane. Its “sand” dunes are made of hydrocarbons, too—the same volatile compounds that give mothballs their distinctive scent, except frozen solid by Titan’s cryogenic cold. The moon’s crust is somewhat more familiar—made of water ice, albeit rendered hard as rock in a deep freeze. So, too, is what the crust hides: a liquid-water ocean much like that found on Earth. Experts expect the water in this sunless subsurface reservoir to be the same temperature as the shallows of the Pacific Ocean.
On Titan, Carl Sagan once wrote,“the molecules that have been raining down like manna from heaven for the last 4 billion years might still be there, largely unaltered, deep-frozen, awaiting the chemists from Earth.” And chemists we will send—robotic ones, at least.
Today NASA announced its New Frontiers selection of a novel mission to Titan called Dragonfly, set to launch in 2026. “This revolutionary mission would have been unthinkable just a few short years ago,” said NASA administrator Jim Bridenstine in a recorded statement. “A great nation does great things. We will launch Dragonfly to explore the frontiers of human knowledge for the benefit of all humanity.”
By the time Dragonfly reaches Titan in 2034, it will have been almost 30 years since Saturn’s satellite was last visited by a spacecraft: the hardy Huygens probe that operated for a few hours on the icy moon in January 2005. The wait, Dragonfly’s scientists say, will be worth it. “NASA has chosen to truly dare mighty things and to rigorously pursue the search for life on this beautiful and bizarre ocean world,” says Kevin Hand, a planetary scientist and Dragonfly team member at NASA’s Jet Propulsion Laboratory (JPL).
The Dragonfly mission’s final competitor for NASA’s coveted New Frontiers selection was a proposal called CAESAR, which had envisioned a sample-return mission to a comet.
Here There Be Dragons
For eons, Titan has been in the clutches of organic chemistry, mixing up cocktails of complex molecules that may well be, at minimum, precursors for truly alien biology—for life as we do not know it. There is scant certainty as to what could await us there—not that this has stopped eager astrobiologists from speculating. “We know Titan has all of the ingredients necessary for life.How far does chemistry get in an environment that has all of the ingredients sitting there?” says Dragonfly’s principal investigator Elizabeth Turtle, a planetary scientist at the Johns Hopkins University Applied Physics Laboratory (APL). “Titan has been doing chemistry experiments for hundreds of millions, if not billions, of years. And what we want to do is go pick up the results of those experiments.”
In a first, this unconventional mission to the outer solar system utilizes modern drone technology. Dragonfly takes after its namesake—an agile flying insect that can soar, hover and perform pinpoint touchdowns. This spacecraft will be at once a drone and a lander, designed to take advantage of Titan’s Earth-like gravitational field and aerodynamics to maximize its ability to explore. For all intents and purposes, the instruments onboard Dragonfly are not terribly dissimilar from those on NASA’s Curiosity Mars rover. Dragonfly, however, is planned to possess the ability to seek out direct chemical evidence of life—so-called biosignatures—regardless of whether that life is based on water and carbon or decidedly more exotic chemistries. And just like Curiosity, Dragonfly will be nuclear-powered, carrying a radioisotope thermoelectric generator. Out at Saturn, the sun’s rays are too faint to reliably power a flying drone—and even if they were strong enough, Titan’s atmosphere is too thick to allow sufficient light to trickle through anyway.
Technically, Dragonfly will be a dual quadcopter, or an octocopter, boasting two sets of four rotors that can transport it to a diversity of geologic regions on Saturn’s moon—although, of course, the mission’s planned sorties are presently hazy outlines. Outfitted with a suite of scientific instruments designed to detect complex organics and biosignatures, Dragonfly will also bring with it the ability to measure seismic activity below Titan’s surface—offering a window into the moon’s hidden, watery ocean.
Taking Titan to the Lab
The year 2034 may seem as far off as Saturn’s mysterious moon itself, but scientists are already preparing for whatever Dragonfly may reveal, in large part by re-creating parts of Titan in the lab. This is particularly challenging, given the extremely cold temperatures on the surface and the immense pressure exerted on the salty ocean below the moon’s icy crust. At the University of Illinois at Chicago, biogeochemist Fabien Kenig and his colleagues have developed a one-of-a-kind experiment designed to replicate the pressures and temperatures of Titan’s ocean within a series of Ping-Pong-ball-sized incubation chambers.
Each chamber will be seeded with microorganisms that thrive in high-pressure terrestrial environments. The team plans to slowly expose incremental generations of those organisms to ever higher pressures and ever lower temperatures, testing the ability of earthly biology to evolve and adapt. Ultimately, the researchers hope to produce populations of microorganisms that might mimic any that exist in Titan’s subsurface waters. A final step would be placing any viable organisms in even harsher Titanian conditionsto test their ability to reproduce and grow. “These types of adaptations can be very useful to understand, so we can better target the types of molecules we would find on Titan,” Kenig says. “Even if it’s very, very slow—when it’s an ice-covered environment that remains stable for millions, billions of years, slowness is irrelevant.”
Kenig’s Titan lab is not alone in trying to simulate billions of years of otherworldly evolution—others exist in some form or another at JPL and APL, and more will now inevitably emerge in preparation for Dragonfly. Each lab’s designs and methods are different, but they all address the same fundamental question: What might life be like on this moon?
New Ways, New Worlds
“The kinds of experiments Titan has been doing take too long to do in the laboratory,” Turtle says. That is why, as far-fetched as it may seem, it is more feasible to “simply” send a nuclear-powered drone more than a billion kilometers across the solar system for direct investigation.
Although Titan’s commonalities with Earth make exploration easier there in some ways, the moon’s bizarre quirks still pose unique obstacles—and opportunities. “There’s an inherent challenge in looking for something that we haven’t seen before. And it’s important to recognize that while Dragonfly has key specific goals of looking for habitable environments and biosignatures, there’s an awful lot of other things we’ll learn about,” says Dragonfly project scientist Ralph Lorenz of APL.
Any forms of life that might exist on Titan should operate in the same way that life does in Earth’s most extreme but survivable environments, seeking out energy sources for maintenance, growth and reproduction—at least, that is Dragonfly’s operating assumption. “Our habitable world has so many different environments that can support life,” Turtle says. “So it’s important to be able to look at this broadly.”
Now that Dragonfly has an official ticket to Saturn, it seems destined to revolutionize not only our understanding of this remote world but also of how planetary science missions can be done. It will not be the first self-powered airborne interplanetary mission (that honor goes to a small pathfinder drone planned for flight on NASA’s Mars 2020 rover), but no other planned or proposed aerial missions have Dragonfly’s lofty ambitions and implications. Over its two-year planned mission, it could traverse the equivalent of the entire length of California, pausing here and there to hover over tantalizing targets and moving every 16 Earth days (or one Titan day) to another far-flung location, gathering data all the while.
Despite the interesting variety of planetary bodies and moons within our reach, there are no other worlds in the solar system that can provide a context for Earth’s formative years as Titan can—a context made all the more urgent as we still grapple with basic questions of what life is and how its animating spark arrives. For decades, we have sought those answers in the laboratory and in some of Earth’s most ancient rocks. But maybe, just maybe, we have now begun in earnest to embrace a better way: flying to the outer solar system, where a pristine billion-year-old experiment awaits. “It’s a place that is at once completely alien and totally familiar because we have these very different materials from what we're familiar with here on Earth undergoing the same processes,” Turtle says.
Dragonfly could be one of the most daring and transformative space missions in our lifetime. “There’s a whole new world to explore that looks awfully like our own in many ways but exotically different,” Lorenz says. A mission to this alien moon will be like stepping into a time machine bound for the deep past, for our own beginnings. It provides a chance to look beyond the horizons of Earth’s geology in search of biology’s cosmic fundamentals: What is life? How does it begin? And if there is life on other worlds, what might it look like? We are now one small step closer to answering the question, blazing the trail for epochal leaps to come.
What is happening on Titan? It is time to go and find out.