When the Perseverance rover arrives on Mars in 2021, the vehicle will land in Jezero Crater and head toward a river delta, a destination offering clues about the planet's habitability.
After studying the region's river, a Stanford University team demonstrated that the Jezero delta is still one of the best places on the Red Planet to search for signs of life.
The Stanford research indicated that river delta deposits within Mars’ Jezero crater formed fast enough to preserve evidence of organics.
Using satellite imagery, the team, led by Stanford professor Mathieu Lapôtre, modeled the amount of time required for the delta's sediment layers to form.
The ancient river on Mars, it turns out, deposited sediment quickly, at least in planetary terms.
Based on the strength of Mars’ gravity, and assuming the Red Planet did not have plants, the scientists estimate that the delta in Jezero crater took at least 20 to 40 years to form. The delta formation, however, was likely discontinuous and spread out across about 400,000 years.
If life once existed near the Martian surface, Lapôtre thinks traces of it could have been captured within the delta layers.
“There probably was water for a significant duration on Mars and that environment was most certainly habitable, even if it may have been arid,” said Lapôtre, an assistant professor of geological sciences at Stanford’s School of Earth, Energy & Environmental Sciences . “We showed that sediments were deposited rapidly and that if there were organics, they would have been buried rapidly, which means that they would likely have been preserved and protected.”
The Stanford study incorporates a recent 2020 conclusion that the researchers made about Earth: Single-threaded sinuous rivers that do not have plants growing over their banks — the same kinds of waterways found near Jezero Crater — move sideways and about ten times faster than those with vegetation.
In an interview with Tech Briefs below, Lapôtre explains how findings from Jezero crater could aid our understanding of life on Mars — and our understanding of how life evolved on Earth.
Tech Briefs: How did you use rivers on Earth and satellite imagery of Mars to model the rivers at Jezero crater?
Prof. Mathieu Lapôtre: As rivers snake through their floodplains, they tend to swipe back and forth across the landscape. This process is called lateral migration. We know that rivers that have wider channels (and thus transport more water and sediments) migrate laterally more quickly.
We also recently found that, on Earth, single-thread rivers forming in barren landscapes migrate laterally at rates about 10 times faster than their vegetated counterparts, for a given channel width. The rivers that build the Jezero delta, on Mars, flowed over 3.5 billions of years ago, and even if life had evolved on Mars, it would have been small and very simple — likely single-cell organisms, or microbes.
Terrestrial rivers forming in barren landscapes thus are good analogs for the Martian rivers that built the Jezero delta. In our study, we scaled the relationship between the width and lateral migration of unvegetated rivers to account for the lower Martian gravity, and combined this new model with observations of the geometry of the ancient river deposits on top of the Jezero delta on Mars. We used detailed measurements and estimates of things like channel width and channel depth that scientists had previously made from high-resolution orbital imagery of the delta.
Tech Briefs: What did you discover about the rate of delta building in the Jezero Crater?
Prof. Lapôtre: Combining our model with orbital observations of channel and deposit geometries, we were able to estimate a rate of deposition for the sediments carried by the rivers. This deposition rate, together with the total thickness of the river deposits, provide a minimum duration for the flows that built the delta. In parallel, we used a different technique that exploits erosion in the catchment of the rivers to estimate the total time span of delta building, including dry spells. We found that flows carrying significant sediment loads and built up the delta lasted for a minimum of 20-40 years (depending on assumptions) spread over a total of ~400,000 years. The uncertainty on the total duration is quite large, but this is our best estimate for the time being.
Tech Briefs: Why is the rate so important to know? Is it basically a confirmation that Jezero Crater is the spot to go to?
Prof. Lapôtre: This is important because it tells us about two important ingredients to a good landing site. First, Mars had surface flows for relatively long periods of time, even if the climate could have been arid. Thus, the surface environment at Jezero was likely hospitable to life. Second, our minimum formation duration allows us to calculate sediment fluxes, and it indicates that sediments were deposited rapidly in the delta. This implies that if life ever evolved on Mars, associated organic molecules would have been buried rapidly in the delta deposits, enhancing their preservation in the rocks, thus optimizing our chances to detect it if it's there!
Tech Briefs: What will the rover do when it gets to Jezero?
Prof. Lapôtre: Upon landing, the rover will be exploring the delta deposits first. This mission is different from previous missions in that, in addition to making observations in situ with the rover payload, the rover will also be sampling and caching the samples for an eventual return to Earth. So the rover team will use to the rover's scientific payload to answer questions about the delta's history from in situ observations as well as selecting promising samples for a variety of questions, including that of life detection. The landing site offers a variety of rock and soil types; sampling this diversity will be important to maximize the science return of the mission.
Tech Briefs: What will be done with any samples?
Prof. Lapôtre: The details of sample handling are still being worked out, but the idea is that a second mission phase will launch a fetch rover to pick the samples up and launch them into Mars orbit, and a third mission phase will go grab the samples and return them to Earth for detailed analyses in laboratories. These subsequent phases are currently in development in collaboration between NASA and ESA.
Tech Briefs: What is a typical day for you?
Prof. Lapôtre: I recently started as an Assistant Professor at Stanford. As such, I juggle between research, research administration, teaching, and advising. There are no two days alike! When I do research, you can find me in the field, in the lab, or in front of my computer. What's truly fascinating about planetary geology is that it lies at the crossroads of many different fields, and allows you to combine a variety of techniques to approach big fundamental questions.
Tech Briefs: What is most exciting to you about the discoveries that are possible with the upcoming Mars 2020 rover mission?
Prof. Lapôtre: Obviously, the big questions we hope to address such as those of Mars' past climate, habitability, and the possibility of detecting ancient extraterrestrial life are all very exciting, and I'd be hard press to pick one. Perhaps what's overall most exciting to me about this rover mission lies in what we'll find that I can't even imagine yet. As a student, I was a member of the Curiosity rover's science team. I never got over the humbling feeling that came with the latest pictures sent back to Earth, every day, knowing that we were the first humans to ever lay eyes on those landscapes.
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