Editor’s Note (8/6/21): Shortly after this story was published, NASA officials announced that data received from Perseverance suggested that no rock was collected during the rover’s initial sampling activity. The Perseverance mission has assembled a response team to evaluate the situation and to plan additional sample collection attempts. This story has been updated to include this new information.
Almost six months into its mission, the Mars rover Perseverance has at last performed its ground-breaking ceremony. Early this morning NASA’s latest emissary to the Red Planet drilled into a rock, then extracted, sealed and stored a pinkie-finger-size sample in a tube within a protective compartment on its underbelly.
At least, that was the intention. Initial images sent back to mission control showed that a drill hole had been created, and telemetry suggested that after the sample was seemingly extracted from the rock, it was processed within the rover according to plan. Some at NASA’s Jet Propulsion Laboratory (JPL) began to publicly celebrate the rover’s apparent success.
But the most recent data and imagery sent by Perseverance indicate that no rock was collected during the drilling—and the mission team are scrambling to find out what went wrong. At this point, the leading theory is that the rock behaved in an unexpected way, as opposed to the rover itself suffering from a mechanical failure.
This seemingly small act of geologic thievery was supposed to mark the beginning of the Mars Sample Return campaign, a multiagency, multimission effort that aims to bring that tube—and many more—back to Earth, giving scientists their first pristine specimens from our neighboring world. For the entire Perseverance team—and most of Earth’s planetary scientists—the significance of this sampling effort cannot be overstated. Perseverance’s initial grab-and-go operation is the opening gambit in a grander quest that could revolutionize our view of Mars—and of life itself. And it was only made possible thanks to the sweat, blood and tears of several generations of scientists and engineers.
“There are hundreds, maybe even thousands of people who contributed at one stage or another” to the mission, says Vivian Sun, the Perseverance science campaign’s co-lead at JPL. “You’re standing on the shoulders of the missions and the teams that have come before you.”
This sample was to be the first of up to 43 that will find their way back to Earth sometime in the 2030s. In specially designed receiving laboratories, these invaluable materials were meant to be forensically examined by scientists hoping to unravel the geologic history of Jezero Crater, a basin strewn with layer-cake-like sediments that was once home to ephemeral lakes and river deltas—and, just maybe, to Martian microbes. It could be that the first definitive evidence of life beyond Earth comes not from anomalous flying objects, mysterious radio transmissions or space-telescope snapshots of exoplanets but rather from microfossils spied in humble rocks from the world right next door.
This is how the sampling attempt happened—and, if future sampling attempts are successful, this is what will happen next.
Choosing the Rock
Until now, Perseverance, or “Percy,” has been busy “settling in” on Mars. While its robotic companion, the Ingenuity copter, has made flight after successful flight around Jezero, Percy has been driving about—sometimes autonomously—taking in the sights, shooting stones with lasers, snapping more than 100,000 photographs, making maps of its surroundings and concocting oxygen from the carbon-dioxide-rich atmosphere.
All of this was but a prelude for its primary mission: to study rocks in search of ancient life. In theory, an epochal finding could come from the rover’s onboard imagers and chemical sensors, but any slam-dunk discovery is unlikely to happen until some of those rocks are brought back to Earth. Of the 43 samples that Perseverance has the capacity to collect, its very first came from an old geologic unit called the Cratered Floor Fractured Rough.
This is the rock type Perseverance landed on back in February. And remarkably, although Percy has been roving across that rock ever since, scientists still know very little about it. They cannot yet say with certainty, for instance, whether it is volcanic in origin—and thus perhaps one of the oldest rocks the rover will encounter—or instead sedimentary, laid down by flowing water or wind over even more ancient material. Solving this fundamental puzzle will help researchers determine exactly how and when the modern-day geology of Jezero came to be. “No matter what it is, it’s got incredible significance for the geologic history of this entire basin,” says Justin Simon, a return sample scientist for Perseverance at NASA’s Johnson Space Center.
Earlier this summer the Perseverance team selected a nearby drill-ready and dust-covered rock from this unit for the long-awaited breaking of ground. After Percy brushed away dust from a small surface patch, the rover lavished the rock with attentions from two gadgets—the Planetary Instrument for X-ray Lithochemistry (PIXL) and the Scanning Habitable Environments with Raman and Luminescence for Organics and Chemicals (SHERLOC) instrument—to learn more about its geochemical composition.
But it was not until now that the “main event” occurred, explains Rick Welch, a project systems engineer for Perseverance at NASA’s Jet Propulsion Laboratory. Late on Thursday, ground controllers transmitted commands to Perseverance to approach and drill into the rock using its two-meter-long robotic arm, extracting a cylindrical core sample similar in dimensions to a piece of blackboard chalk. Passed between multiple chambers by a second, stubbier robotic arm on the rover’s underbelly, the sample was sized up and photographed before finally being hermetically sealed and cached.
From core to cache, the process took less than eight hours to complete—an impressive feat of engineering that was not lost on scientists watching from afar, particularly those keen to see if these invaluable rocks contain evidence of life. “They are drilling into the surface of Mars, for God’s sake,” says Jonathan Eisen, an evolutionary biologist at the University of California, Davis. “I mean, it’s amazing!”
It of course comes as an unpleasant surprise that the rock sample itself appears to have gone missing. Scientists and engineers will spend the next few days trying to work out what went wrong—and when the time is right, they will try to sample the rock again.
“While this is not the ‘hole in one’ we hoped for, there is always risk with breaking new ground,” said Thomas Zurbuchen, associate administrator of NASA’s Science Mission Directorate, in a recent statement. “I'm confident we have the right team working this, and we will persevere toward a solution to ensure future success.”
Looking for Life
Current plans call for some of the rover’s samples will be left somewhere in Jezero, while others will be kept onboard Perseverance. Circa 2028 the European Space Agency’s autonomous Sample Fetch Rover should scoop most or all of them up for delivery to a nearby Mars Ascent Vehicle sent by NASA, after which they will be launched into orbit. There, a European spacecraft will track and collect the sample container like a baseball glove catching a ball and then return to Earth. The samples should touch down in a desert in the American West—most likely one in Utah—as early as 2031.
Presuming a sample is ultimately retrieved, this first specimen from the Cratered Floor Fractured Rough is unlikely to contain evidence of life, Sun says, particularly if the rock has volcanic origins—a lava flow, for example. The most astrobiologically promising targets are in Perseverance’s future: parts of the former lake bed that once accumulated sediment and the ancient river delta that channeled this material from surrounding regions. Those, too, are thought to offer slim chances for any extant organisms, however, because of Mars’s arid, frigid, irradiated surface conditions. Any living microbes would presumably lurk inaccessibly deep belowground, in the planet’s warmer and possibly wetter interior. That is why, if anything living is found in Percy’s rock samples, it will almost certainly be biological contamination from Earth, Eisen and others say.
The chance of finding signs of ancient life is, of course, unknown. But Mars once had a radiation-deflecting planetary magnetic field and much more surface water. Whether life was delivered to a youthful Mars via meteorites coming from a young Earth or independently arose on the Red Planet, many experts suspect it would have had good chances at thriving during the world’s earlier epochs. “I don’t think it’s actually that unlikely we’d find evidence for past life,” Eisen says.
Compared with hunts for primordial life back on terra firma, it may actually be easier to find ancient biology on Mars, Simon says. Earth’s constantly moving tectonic plates have destroyed most of its original crust, effectively wiping our planet’s earliest geologic eras from existence. Mars does not seem to have ever had plate tectonics, so the ancient landscapes that may have been home to life are still around today—assuming they have not been covered by lava or mangled by impacts.
Whether remotely on Mars or directly back on Earth, when astrobiologists study Perseverance’s rocky haul, what exactly will they be looking for? Mineral-rich structures created by microbes are one obvious target, says María-Paz Zorzano, a researcher at Spain’s Center of Astrobiology and a European return sample adviser to the Perseverance team.
Optimistically, those structures would resemble Earth’s stromatolites, layered mounds of microbes that, although rare today, appear as abundant fossils in certain 3.5-billion-year-old rocks. But no one is betting on such a conclusive find: most other purported examples of very old, biologically created mineral structures are the subject of intense debate. Right here on our own planet, structures suggested to be of organismal origins are often later shown to have abiotic provenance. Stretching such extrapolations beyond Earth—as in the now infamous case of putative microfossils in a Martian meteorite—is a shaky prospect indeed.
That is why any suspect structures will likely need corroboration with biomarkers—molecules that somehow signify life’s presence. Familiar biochemical mainstays such as DNA, RNA and proteins are poor candidates for such searches, being vulnerable to degradation by radiation and geologic activity. Lipids—fats used in cell membranes—can be preserved for far longer and thus could be used as a marker of ancient life, Zorzano says. Collections of other chemicals associated with life, including phosphorous, sulfur and assorted nitrogen-based compounds, may also persist through the eons. The same longevity could apply to variations of elements that life as we know it prefers—lighter types of carbon, for example. Chlorophyll and other biological pigments used to absorb particular wavelengths of light are also known to remain somewhat intact across geologic time.
Such detective work would be easier if life on Mars resembles life on Earth, Zorzano says. But Martian microbes may strongly diverge from the designs of terrestrial microorganisms, requiring more “agnostic” life-identifying experiments built on still hazy assumptions of what, if any, physical rules apply to all instances of biology across the cosmos.
Even leaving aside the decade-spanning timeline for returning the samples to Earth, investigating them for ancient life will be a long, drawn-out process: month-by-month, year-after-year, one after another, each and every plausible nonbiological explanation for any suspicious-looking patches of rock must be ruled out. Meanwhile any supposed biomarker must still fit within the planet’s broader context: if a “smoking gun” signature of ancient biology just occurs in rocks recording conditions otherwise known to be hostile to life, researchers will have only succeeded in finding even deeper mysteries to puzzle over and study for generations to come.
Scientists may not discover signs of Martian life. But, just maybe, they might succeed in doing so. If such a finding is shown to have a common evolutionary lineage with life on Earth, that will be one thing: at minimum, we will then know we are not alone in the universe. But if we find life that arose independently on Mars, “the value of that from a scientific and philosophical point of view is going to be off the charts,” Eisen says. Such a discovery would strongly suggest that life can spring up almost anywhere like flowers that always seem to be sprouting from long-forgotten brick walls. Life could be the rule, rather than the exception, throughout the universe.
The Mars Sample Return journey has only just begun. And as the difficulties in this first collection attempt have demonstrated, the end of the road is still far beyond the horizon. Those following it have no guarantee of reaching any astrobiological promised land. But dreaming of the day alien life may be discovered hiding in Martian rocks is an undeniably beguiling thought. “Statistically, there has to be life in the universe. It’s so big; there just has to be,” Eisen says. “But that doesn’t mean anything until you actually find evidence for it.”