For the past few decades, rovers and landers on Mars have focused on finding out whether the planet was habitable for life in the distant past. Not since the Viking landers in the late 1970s/early 1980s has there been a direct search for evidence of life, until now.
NASA’s upcoming Mars 2020 rover (as well as ESA’s ExoMars rover) will look for evidence of past microbial life when it lands on Feb. 18, 2021 in Jezero Crater. This crater once held a lake and river delta, and the sediments still there are a prime location to search for such evidence.
Now, a new study, published on Nov. 12, 2019 in the journal Icarus, shows that Jezero Crater may be an even better location than first thought. Concentrated deposits of carbonates have now been identified along the ancient shoreline of the former lake. The deposits trace the shoreline like a bathtub ring.
On Earth, such deposits are ideal for preserving fossils of seashells, coral and some stromatolites (distinct rock formations created by microbes). The carbonates had been identified previously from orbit, but the new study shows interesting concentrations of them along the old shoreline. During its mission, the rover will be able to visit other deposits of carbonates as well, not just the ones along the shoreline.
“CRISM spotted carbonates here years ago, but we only recently noticed how concentrated they are right where a lakeshore would be,” said the paper’s lead author, Briony Horgan of Purdue University in West Lafayette, Indiana. “We’re going to encounter carbonate deposits in many locations throughout the mission, but the bathtub ring will be one of the most exciting places to visit.”
The greatest concentration is along the crater’s western rim, called “the marginal carbonate-bearing region.” It’s possible the carbonates were deposited before the lake formed, but the rover will be able to determine if they really were formed in the lake or not.
“The possibility that the ‘marginal carbonates’ formed in the lake environment was one of the most exciting features that led us to our Jezero landing site. Carbonate chemistry on an ancient lakeshore is a fantastic recipe for preserving records of ancient life and climate,” said Mars 2020 Deputy Project Scientist Ken Williford of NASA’s Jet Propulsion Laboratory in Pasadena, California. JPL leads the 2020 mission. “We’re eager to get to the surface and discover how these carbonates formed.”
Mars 2020 will also visit the delta, where river water once fed into the lake, just like deltas on Earth.
While carbonates are great for preserving signs of life, they also can provide clues as to how Mars lost most of its atmosphere, which turned the planet from a once warmer world with a thicker atmosphere and water on the surface, to the cold desert it is today.
The carbonates aren’t the only thing the scientists are interested in. There is also a deposit of hydrated silica on the edge of the delta, which would also be ideal for preserving evidence of ancient life. That would be especially true if the deposit turns out to be on the bottom layer of the delta.
AmericaSpace asked astrobiologist Nathalie Cabrol, Director of the Carl Sagan Center for the Study of Life in the Universe at the SETI Institute, what her thoughts were on the landing site of Mars 2020 and its potential for preserving clues of possible ancient life:
“The Jezero site is a wonderful site for a number of reasons. Chiefly, the presence of a deltaic deposit in a basin is pretty much ideal when you are looking at understanding environmental evolution. Moreover, that deposition happened really at a key time in the history of Mars. 3.6 billion years ago, Mars was going through a profound climate change that led to the conditions we know now. Jezero might have the record of not only seasonal cycles of flow since the hydrological activity was sustained over long periods of time (maybe 2-3 million years if the assessments are correct), but maybe also signs of those changes at planetary scales. To me, this is really exciting. Also, the impact excavated fairly ancient materials and that will give us a window into deep times on Mars. That’s for the environmental part.
When it comes to life, conditions for the inception of life where more favorable early on Mars. Jezero was formed at the tail end of Mars habitability, and deltas are fairly disruptive and dynamic environments. They build a lot but destroy a lot as well. So, it will take great detective work and attention to details to reconstruct what is found. This being acknowledged, lacustrine basins are little oases of their own and, depending on the composition of the water column, they can provide decent shelters to life, especially if there are lots of dissolved solids in the water, which you would expect in an environment like Mars at that time.
There is also a lot we do not know or understand about life and prebiotic chemistry. It could very well be that the impact itself generated enough energy for hydrothermal processes for a long while in that basin and provided conditions for life; or it could be that life that had been dormant in that region and was reactivated during the lifetime of Jezero. We simply do not know and this is what makes it really exciting.
What we know, however, is that the mineralogy in and around Jezero is one of the best we can hope for to search for biosignatures. Carbonates have been hard to find on Mars and this will put another point on our graphs. That actually is a lot more than it sounds. Their presence is evidence of a watery past and a thicker atmosphere on the red planet. The silica deposits are extremely exciting, because they are excellent at preserving the record of life.
Ultimately, we still have to remember that Mars was a different planet than Earth – always. It also became a lot more extreme very rapidly. There are also many questions we still have to answer for our own planet when it comes to the origins of life, or how much organic matter was created early on. We do not know what’s out there, and we do not have the answer to these questions but we have to start somewhere and Jezero is one very exciting site to do just that.”
NASA’s Spirit rover also found silica deposits during its mission, ones which are very similar to those found in hydrothermal spots on Earth. They even bore some similarity to silica formations known to be created with the help of microbes, although Spirit couldn’t make that determination with the equipment it had.
Mars 2020 will not only analyze samples it takes from rocks and soil in its onboard laboratory, it will also store some of those samples in small tubes that could then be retrieved by a later mission and brought back to Earth for even closer study.
Mars 2020 will also carry the first-ever quadcopter to Mars, a small drone-like helicopter that will scout areas of interest from above for the rover to explore. It was attached to the belly of the rover last August.
The Mars 2020 mission follows the Curiosity rover, which landed in 2012 and is still busy today exploring Gale Crater. Curiosity has found abundant evidence for a more habitable environment in that region of Mars millions or billions of years ago.
Mars 2020 will be launched from Cape Canaveral, Florida in either July or August 2020, and land on Mars on Feb. 18, 2021.
More information about the Mars 2020 rover is available on the mission website.