At a recent workshop in Washington, D.C., on the science of NASA’s Mars Sample Return (MSR) program, the mood was excited but tense. The space agency had just dropped a bombshell announcement that it was looking for “outside the box” proposals from private industry to reboot its troubled plan of bringing back Martian rocks to Earth. None of us were exactly sure what this meant, so we tried to focus on the science, but speculation on the fate of the U.S. Mars program was hard to avoid.
Bringing back rocks from another planet will be the most ambitious thing that NASA has attempted since the Apollo program. Pursued in partnership with the European Space Agency, MSR is a key stepping stone in the path towards sending humans to Mars, and eventually to other places in the solar system. But the eye-watering estimated price tag for the original MSR plan—between $8 and $11 billion, all to retrieve a few kilograms of rock, soil and Mars air no earlier than 2040—has left many policy makers, and even a few scientists, wondering if the benefits really outweigh the costs.
Outsourcing some of the heavy lifting to companies such as SpaceX and Lockheed Martin could perhaps be a faster and cheaper way to bring MSR’s precious cargo back home. But there’s no avoiding the fact that doing big things in space is always expensive: adjusted for inflation the James Webb Space Telescope (JWST) cost about $10 billion, while the entire Apollo program cost more than $250 billion. In these and many other cases, sharp criticisms of the high cost faded with hindsight, as the true impact of each project’s monumental achievements became clear. Because MSR’s scientific, technological and even political implications are so far-reaching, I believe we’ll see it in just the same way in years to come.
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Mars is scientifically important because it allows us to study what makes a planet habitable over time. The Red Planet had rivers, lakes and possibly even oceans in its early history, but because of its small size and distance from the sun, it cooled and lost much of its atmosphere within the first billion years of its life. This transformed Mars into a much harsher place, but it had the fortuitous side-effect of preserving the planet’s ancient habitable past right on its surface. Plate tectonics and erosion have chewed up most of our home planet’s ancient rock record, but on Mars we have a window into the early solar system that goes back four billion years—the same time life was first emerging on Earth.
Explaining why Mars had ancient rivers and lakes is a long-standing problem in planetary science. As far back as 1972, Carl Sagan and George Mullen noted that because the young sun was fainter than it is today, early Mars should have been extremely cold, unless its climate was radically different. Today, there are several promising solutions to this problem, but still no consensus on which is the correct one.
Sample return will tackle this question head-on, because it will allow us to study ancient Mars rocks as never before, seeking chemical clues on the nature of that world’s early atmosphere and climate. Many samples are already packaged in tubes and awaiting retrieval from the vicinity of Mars’s Jezero Crater, the site of a now-vanished ancient lake where NASA’s Perseverance rover has been operating since 2021.
Perseverance’s in situ studies of the samples already hint at the ancient lake’s highly dynamic environment, and the minerals preserved in these rocks represent a treasure trove for future scientists to examine. For example, measurements of trace isotopes can reveal the composition of the ancient atmosphere, constrain the timing of key geological events and even tell us the temperatures at which minerals in sediments formed. Techniques for this kind of work on Earth are now highly advanced, but they require large laboratories and heavy, finely calibrated instruments, ruling them out for use by robotic landers and rovers.
The early habitability of Mars is particularly important because of its implications for planets and life elsewhere in the universe. The latest observations by JWST are suggesting that just like Mars, many small rocky worlds around other stars have lost much of their atmospheres, too. Solving the problem of Martian habitability can therefore also help us to understand whether life could exist on such planets.
MSR’s most revolutionary possible result would of course be a direct discovery of ancient Martian life. This is far from guaranteed, but it’s entirely possible, as early Mars likely had all the ingredients necessary to kick-start prebiotic chemistry. In a 2021 study California Institute of Technology researcher Danica Adams and her colleagues showed that the early Martian atmosphere could have produced biologically significant quantities of hydrogen cyanide—a compound that despite being toxic to humans was probably essential to the origin of life on Earth. In another recent study, Penn State professor Chris House and colleagues found suspiciously lightweight carbon isotopes in samples of organic material from Gale Crater, where Perseverance’s older sibling Curiosity is still exploring. This enrichment could be a consequence of unusual atmospheric chemistry, or it could have been caused by the presence of ancient microorganisms that preferentially consumed the lighter form of carbon, just as life on Earth does. Detailed study of returned samples will allow us to address these and many other questions about chemistry and life on early Mars.
MSR is ambitious in the way that all great science must be. It will open the door to a huge range of new possibilities in both robotic and human exploration beyond Earth’s orbit. As shown by the recent success of China’s remarkable Chang’e 6 mission, which has just returned the first-ever samples from the far side of the moon, 21st-century planetary science is now a truly international endeavor. The U.S. has led the way in Mars exploration for decades, but Mars too is now a target of interest for multiple countries, including China, which is planning a sample-return mission of its own that would bring back rocks from the Red Planet in the 2030s. Maintaining U.S. leadership in Mars exploration is absolutely possible, but requires foresight and renewed commitment from policy makers, starting now.
This is an opinion and analysis article, and the views expressed by the author or authors are not necessarily those of Scientific American.