When Mars 2020, with the Perseverance rover onboard, lands on Mars tonight, it will be NASA’s ninth mission to do so. But this will be the most ambitious. In addition to studying the geology and climate of the red planet, and paving the way for human exploration beyond the Moon, the rover will look for traces of microbial life that may have lived there billions of years ago. It will collect rock samples in metal tubes and future missions will return them to Earth for further study. To quote Carl Sagan,” says Gentry Lee, chief engineer of the Planetary Sciences Directorate at NASA’s Jet Propulsion Laboratory (JPL), “if we see a hedgehog looking at the camera, we would know that there is current life and certainly ancient on Mars, but based on our past experiences, such an event is extremely unlikely. Extraordinary claims require extraordinary evidence, and the discovery that life existed elsewhere in the universe would certainly be extraordinary.
A promising crater, Scientists on the Mars 2020 mission believe that the Jezero crater, Perseverance’s landing site, could host such evidence. They know that 3.5 billion years ago, Jezero was the site of a great lake, with the delta of a river. They believe that while the water may have disappeared a long time ago, somewhere within the 45-kilometer-wide crater, or perhaps along its 610-meter-high rim, biosignatures (evidence that life once existed there ) could be waiting.
“We hope that the best places to look for biological signatures are in the bed of Lake Jezero or in sediments off the coast that could be encrusted with carbonate minerals, which are especially good at preserving certain types of fossilized life on Earth,” says Ken. Williford, project scientist at JPL. But while looking for evidence of ancient microbes on an ancient alien world, it is important to keep an open mind. The rover, the fifth to circulate the red planet, carries a new set of scientific instruments that build on the discoveries of its predecessor, Curiosity. This rover, still in old age, discovered that parts of Mars could have supported microbial life billions of years ago.
Any biosignature search will include the rover’s camera suite, especially Mastcam-Z (located on the mast), which can be zoomed in to inspect scientifically interesting targets. The mission’s science team may commission Perseverance’s SuperCam instrument, also on the mast, to fire a laser at a promising target, generating a small cloud of plasma that can be analyzed to help determine its chemical composition. If that data is intriguing enough, the team could command the rover’s robotic arm to zoom in for a closer look.
To do that, Perseverance will lean on one of the two instruments in the turret at the end of his arm. The first is PIXL, which will use its small but powerful X-ray beam to search for possible chemical fingerprints from past lives. The second is called SHERLOC, it has its laser and can detect concentrations of organic and mineral molecules that have formed in aqueous environments. Together they will provide high-resolution maps of elements, minerals, and molecules in Martian rocks and sediments, allowing astrobiologists to assess their composition and determine the most promising nuclei to collect.
Biological processes, The team is hoping to find a surface feature that cannot be attributed to anything other than ancient microbial life. One of those features could be something like a stromatolite. On Earth, stromatolites are wavy rock mounds formed long ago by microbial life along ancient shores and in other settings where metabolic energy and water were abundant. Something so striking would be difficult to attribute to geological processes. Yes, certain forms originate in rocks where it is extremely difficult to imagine an environment devoid of life that could cause them, ”says Williford. “But that said, there are chemical or geological mechanisms that can cause vaulted layered rocks like what we normally think of as a stromatolite.
Perseverance will collect the most intriguing samples it can find, store them in metal tubes, and then deposit them somewhere for future missions to collect and bring them back to Earth for analysis. The instrumentation needed to definitively prove the existence of microbial life on Mars is too large and complex to bring it to Mars,” explains Bobby Braun, director of the Mars Sample Return program at JPL. “That is why NASA has partnered with the European Space Agency in a multi-mission effort to retrieve the samples collected by Perseverance and bring them back to Earth for study in laboratories around the world.”
When that happens, samples from the Perseverance rover on Mars will be able to tell us that at one point, billions of years ago, life existed in other parts of the universe. But they can also indicate the opposite. We have strong evidence that Jezero Crater once had the ingredients for life. Even if we conclude after returned sample analysis that the lake was uninhabited, we will have learned something important about the extent of life in the cosmos, ”says Williford. ‘Whether Mars was a living planet or not, understanding how rocky planets like ours form and evolve is essential. Why did our planet remain hospitable when Mars became a desolate wasteland?