With a five-meter-wide, 57-meter-tall rocket waiting to blast off from China’s southern island of Hainan, the nation is quietly making final preparations for its first independent trip to Mars. When the launch window opens in mid-July, Chinese scientists will strive to send a probe to a planet that confused their ancestors with its constantly changing brightness and position in the sky.
The spacecraft, called Tianwen-1, or the “Quest for Heavenly Truth,” will carry 13 scientific instruments to examine the Red Planet from orbit and on its surface. Tianwen-1 will examine how water ice is distributed on Mars, as well as the planet’s physical evolution and its habitability over time. The mission—consisting of an orbiter, lander, and rover—is “the most ambitious thing one could do on a first attempt,” says John Logsdon, a space policy expert at George Washington University.
Troubling Track Record
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The odds of a flawless mission are daunting: Of humanity’s dozens of attempts to orbit or land on Mars to date, only about half have succeeded. After some high-profile setbacks, NASA has deployed five landers, four rovers and multiple orbiters that have brought the world to life for scientists and the public alike. But China’s spacefaring experience beyond Earth orbit has been limited to several robotic moon missions and an orbiter that piggybacked on a failed Russian mission to the Martian moon Phobos in 2011.
Two major risks confront the five-metric-ton Tianwen-1, Logsdon says. First, China’s most powerful heavy-lift rocket, Long March 5, has only launched three times—including a major failure in 2017, when the rocket started to malfunction shortly after takeoff. It took more than two years for scientists to fix Long March 5’s core-stage-engine problem and score a successful flight in late 2019. Its track record makes observers nervous, however.
Second, Tianwen-1’s lander must navigate the challenging Martian atmosphere, which is thick enough to overheat the probe but too thin to decelerate it sufficiently. The spacecraft’s entry, descent and landing technology uses a heat shield, a parachute and a retro-engine to slow its descent, an arrangement resembling that of earlier U.S. missions. Yet when the vessel is just 100 meters above the surface, it will pause, take snapshots of the area and quickly calculate the best landing spot. Then it will shift horizontally to center above that spot and carefully touch down with the lander’s four legs.
In November 2019 China tested this part of the landing procedure, which the nation had previously used successfully in its moon landings, in the province of Hebei. Foreign officials were invited to watch the test on-site. It was the last major public event for Tianwen-1, however. Since then, the China National Space Administration (CNSA) has kept a low profile, and mission scientists have declined or ignored nearly all interview requests.
Scientific Opportunities
Should Tianwen-1 land successfully, its research could illuminate new aspects of Mars. For instance, both the orbiter and the rover are equipped with a ground-penetrating radar to chart geologic layers under the surface. The radar on the orbiter can “see” as deep as a few thousand meters, whereas the instrument on the rover has a shallower view but sharp centimeter-level resolution. “China’s main goal [with these radars] is to explore the water-ice layer” under the planet’s surface, says Wlodek Kofman of the Institute for Planetary Sciences and Astrophysics of Grenoble in France.
Tianwen-1’s ability to measure Mars’s magnetic field excites Jim Bell of Arizona State University, principal investigator of the main camera on NASA’s Perseverance rover. One prevailing hypothesis is that the Red Planet used to have a global magnetic field like Earth's, he says. When its smaller molten iron core cooled down, however, Mars gradually lost this shield, exposing the world to solar wind and radiation, thinning its atmosphere and dooming any water that might have flowed on its surface. Since 2014 NASA’s Mars Atmosphere and Volatile Evolution (MAVEN) mission has found ample evidence to support this scenario, but scientists crave a fuller picture. “Tianwen-1 will be very useful in providing more evidence from a different orbit and from the ground,” Bell says. He hopes the Chinese team will share data with the international community piecing together the environmental evolution of Mars.
Tianwen-1 will aim to land in the southern part of Utopia Planitia, a largely flat area between 25 and 30 degrees north of the Martian equator. Geologists have long suspected that this region is covered with ancient mudflows, pointing to stores of bygone water. “It’s an interesting place to investigate potential past subsurface habitability,” says Alfred McEwen, a planetary geologist at the University of Arizona.
First in a Series
The rover’s chance of finding water beneath Mars might be limited by its latitude, McEwen notes. Because it draws its power from solar panels, it must stay near the equator. Today water ice below the planet’s surface, most researchers believe, remains mainly at higher and cooler latitudes.
Tianwen-1’s reliance on the sun compelled its team to design hardy instruments, says Rong Shu of the Shanghai Institute of Technical Physics at the Chinese Academy of Sciences. “Since our rover does not have radioisotope power, all the instruments need to endure temperatures as low as –90 degrees Celsius while at rest, and they operate in the temperature range of –40 to –30 degrees C,” he adds.
The rover's payload includes the Martian Surface Component Detector (MarSCoDe), whose design was led by Shu. Similar to ChemCam on NASA’s Curiosity rover, MarSCoDe can fire short laser pulses to vaporize the surfaces of rocks from a few meters away. The instrument will “sniff” the ionized gas produced by these mini blasts and determine the type and quantity of chemical elements in the rocks.
Tianwen-1 is expected to reach Mars in February 2021. It will spend about two months in a parking orbit, waiting for the best timing and surface conditions to land. China’s expanding radio telescope network of tracking and receiving stations will sustain communications between Earth and the probe.
Already, Chinese scientists are preparing for more missions in the Tianwen series, including ventures to return rock samples from Mars and an asteroid, to perform a flyby of Jupiter and to explore the margins of the sun’s vast heliosphere. But if Tianwen-1 reaches Mars as planned, Logsdon says, “it will put China in the space exploration business in a big way.”