After 20 years of continuous investigation of the Martian surface with robot geologists, NASA’s Mars exploration program has hit a snag. Perseverance, the latest and most advanced rover in a series that began with Spirit and Opportunity in 2004, is working fine, don’t worry. It’s what comes next that’s in doubt.
In September 2023, an independent review panel concluded that NASA’s planned mission to collect rock samples collected by Perseverance and return them to Earth is not feasible given the current timeline and budget. Not even close. Returning the sample as currently conceived would cost up to $11 billion, double the original estimate, and presents serious technical problems that would have to be resolved first. Not to mention still unresolved questions about planetary protection – concerns that Martian rocks returning to Earth could contain a biological payload.
The complexities of sample return missions
Returning samples, the cornerstone of NASA’s long-term strategy for Mars, has been a calculated risk since NASA and the US Congress decided to proceed with the first part of the mission (sample collection) without a firm plan. and secured financing. to bring them back. Perseverance has already deposited more than 20 carefully selected samples on the surface of Jezero Crater, awaiting later collection. But an even more daunting sequence of tasks – collecting them, launching them into Mars orbit, returning them safely to Earth and then equipping laboratories with sensitive instruments to analyze them – still lies ahead. This is the part that is proving difficult.
Over the past two decades, advisory committee after advisory committee has insisted that a sampling mission is necessary to determine whether life ever existed on Mars. However, the committees also stipulated that the sample return should not come at the expense of other NASA planetary missions, which have already had their launch dates postponed.
This is not the first time that NASA has struggled with the complexity of a Mars sample collection mission, and it remains as cumbersome as ever. The cost overruns are no surprise. In the past, Congress might have simply sighed, decided the project was too big to fail, and appropriated the extra money. This time-honored tactic may no longer work, however. Even before problems arose with the sample return mission, Congress and the White House told NASA to expect leaner budget years.
Detecting active life on Mars
So this might be a good time to pivot. NASA’s Mars program has thus far focused primarily on looking for evidence of past life. There is another, more exciting possibility: that life exists on Mars. today. A proposed mission more in line with this idea is the Mars Life Explorer (MLE), which would look for signatures consistent with current life on Mars. The MLE concept was highly rated by the latest “decadal research” advisory committee for consideration as the next Mars mission after sample return. If it appears that the sample return will be greatly delayed or even canceled, NASA must ensure that others in line can still move forward.
An MLE mission, estimated at one-tenth the cost of a sample return, could potentially do a rapid analysis for signs of current biology. A lander could be sent to Jezero Crater or any other location already visited by NASA rovers to build on the years of work and billions of dollars already spent characterizing the site. In fact, such a mission could land almost anywhere on Mars, since water – considered fundamental to biology – appears to be widespread beneath the Martian surface. A recent analysis by Michael Mellon of Cornell University and colleagues concluded that “all latitudes offer some potential for exploring life.” Alternatively, the MLE could be sent to areas where salt deposits may harbor microbial life that draws water from the atmosphere.
A July 2023 report on possibilities for future missions to Mars revealed “a genuine enthusiasm for maintaining life detection within the program, given the significant progress that has been made in life detection technology in recent years.” In fact, methods for conducting biological investigations on Mars have only improved since proposals like the Icebreaker Life Mission began emerging about a decade ago.
Even bolder than MLE would be a mission to search for active life on Mars, analogous to what Viking attempted half a century ago. Viking couldn’t definitively resolve the question of life or not, largely because we knew little about Mars at the time. Thanks to missions like Curiosity and Perseverance, today we understand the environment much better.
At the same time, life detection technology has advanced greatly since the 1970s. Certainly, finding life in a hostile, nutrient-poor environment like Mars will still be a challenge, but a new generation of instruments currently in development that could be small and light enough to fit on a spacecraft, gives us hope.
Nanopore sequencing technology, for example, could detect DNA in the Martian environment, which would indicate the presence of life – at least the kind of life we know here on Earth. Furthermore, we should consider tools that could directly detect active organisms. If there are microbes on Mars, we want to see them. We could, for example, ship a high-resolution digital holographic microscope that has no moving parts and has a higher throughput than traditional microscopes. Another technique would be to track the movement of supposed microorganisms against the natural background, which could be done with greater than 99% certainty. We might even be able to see movement inside cells. A biology-focused mission that combines several independent detection methods has a good chance of finding life on Mars, if it exists.
Where would this leave the sample return project? Assuming the technical and organizational issues can be resolved, this mission could not launch before 2030, according to the recent review. Meanwhile, China plans to launch its own Tianwen-3 Mars sample collection mission in 2028, the same year that the European Exomars rover is expected to launch. It’s even possible — though far from certain — that SpaceX’s Starship could be in service by the early 2030s, which could alter the logistics and costs of Mars exploration so dramatically that any future NASA missions would likely would need to be rethought anyway.
So far in the 21st century, NASA’s Mars program has focused on understanding the planet’s geology, and for good reason. Before determining that a rock contains evidence of life, scientists need to understand the environment in which it was found. NASA’s robot geologists developed prior knowledge, so it was easy to justify in this sense. We still don’t know if there is biology on Mars, so a life detection mission is still a speculative bet.
But the characterization of the place, as important as it is, cannot continue forever. The only reason Mars remains at the top of NASA’s to-do list is the possibility of us finding life there. Almost no one, even in the planetary scientific community, would spend $11 billion just to study the detailed geological history of an arid world. The exploration of Mars is – and always has been – about looking for life. We should get on with it.