Not individual cells, unless the cells are very large, and we don't expect to see something like that. In fact, one of the main reasons to get the samples back to Earth is so we can use light microscopy and spectroscopy to get higher spatial resolution, even down to nanometer-scale resolution. With spatial resolution like that, we can distinguish individual fossil cells quite well. There are many examples of them on Earth. Some of the oldest sedimentary rocks on Earth have fossil bacteria in them.
What we can see on Mars with Perseverance is larger-scale structures that can be formed by single-celled organisms, like microbial mats. We absolutely can see things at that scale. Those are almost meta-shapes formed by those little cells. Those structures can be really ambiguous, though. The controversy over the life-like structures in the Mars meteorite, Allan Hills , is still unresolved 25 years later.
Yeah, absolutely. We think about the Alan Hills meteorite a lot. It launched a lot of interesting science and in some sense was really responsible for the expansion in the field of astrobiology. The funding that paid for PhD work may well not have existed had it not been for that.
It set into motion the approach I just described, looking for both lifelike shapes and lifelike compositions when they occur together. I think some people oversimplify the history of the meteorite [and the reported claim of fossil life from Mars]. There was a lot more to that paper , if you go back and look at the details.
I'm going to give away my age and let you know that I was at that press conference in Humans are fantastic pattern-recognizers. We see things that aren't there all the time. I'm looking out my window right now at shapes I can see in the clouds and that sort of thing.
So we have to be vigilant against fooling ourselves, but at the same time, if we completely shut down our visual sense and say, "Don't believe what you see," then we're really at risk of missing big things. It's one of the most interesting challenges we face with Perseverance: How do we be stay open to interesting things on Mars without unduly fooling ourselves? What might a truly meaningful mineral or structural relic of ancient life look like?
There are a number of minerals that we often find associated with signs of ancient life on Earth. Carbonates are a big one. On Earth, seashells are made of carbonate minerals. We don't expect to find large, complex animals of the kind that form seashells on Mars, but even the oldest stromatolites [sedimentary structures associated with bacteria] are formed from carbonate minerals that have later been partially silicified.
Porous fossil microbial mats contained carbonate minerals and some fluids with dissolved silica flowed into them. In some cases, the silica precipitated out, replaced some of the materials in the stromatolite, and led to it being preserved in a way that it otherwise might not have been, as microcrystal and quartz. Then there are sulfate and sulfide minerals, sulfur-bearing minerals in both the oxidized and the reduced phases.
One way to look at it is, you could boil it down to the chemical elements that you're interested in. We have carbonates, sulfates, phosphates, and so on. There are many others. Any case where you can get redox couples, so oxidation and reduction chemistry transforming something like a sulfate into a sulfide, any chemical reaction like that is something that a microbe can make its living from.
And is there a tension between the two goals? Well, geochronology lies in the realm of planetary evolution, understanding what the interior of Mars is made of and how that's evolved over time. But these big, broad questions are also critical to astrobiology; all of these processes enable and regulate the habitability of a planet. How did the non-living systems on the planet evolve and change in a way that caused the planet to be habitable, or that caused that habitability to collapse?
Then again, the best samples for geochronology may not be best for preserving signs of life. A natural dynamic tension exists there. The way I think about it, coming more from the astrobiology side, is just as I said: All that stuff is completely critical to the signs of life and understanding their context. It's all just big, beautiful science as well. Jezero crater as it may have appeared 3.
Why did you choose this particular location? Well, it very clearly was once a crater lake. There's an ancient river channel flowing into it from the northwest.
Less obvious, there's an outflow channel in the northeastern corner of the crater. Then there's this big, beautiful delta. If you find a delta at the end of a river system inside a basin like a crater, it says there was a standing body of water here that was met by a flowing body of water. In this case, a lake is met by a river, and the river is capable of carrying all that entrained sediment because there's energy of flow.
Then when it hits the standing water, the energy drops and the sediment drops out in a big pile, just like where the Mississippi Delta meets the Gulf of Mexico. So that's Jezero itself, but it's zooming out to the broader region around it that really led us here in the first place.
The crater sits within a region that offers access to not only the earliest interval of Mars' history but a younger interval where we have the Syrtis volcanic province [when the huge Martian volcanoes erupted]. Jezero is situated between Isidis to the northeast of Jezero and the Syrtis volcanic province to the southwest. Materials from that volcano would've been interacting and the impact of that volcanism on the Martian environment would have been recorded to some extent in the rocks around Jezero.
Is it possible to deduce how long ago Jezero crater was a lake, and how long that wet period lasted? Our best estimate so far for the age of the Isidis impact, which has to have been earlier than the Jezero impact, is about 3. We are not about the absolute age of Jezero, however. The estimates range as old as 3. Interestingly, that is the time when we find the first evidence of life on Earth. Perseverance is bringing along an experimental helicopter called Ingenuity.
Will it help you locate interesting places to explore? Ingenuity has a well-defined mission that it plans to execute over 30 sols [Martian days] with five flights of increasing complexity. The mission there is to demonstrate that that flying technology can work on Mars. It would be really powerful in enabling future helicopters that could land and be a major component of the science exploration.
We're all rooting for the team and can't wait to see the images that result, but it's not a component of our science mission planning. What makes Jezero crater such a significant place to go prospecting for evidence of ancient Martian life?
Jezero offers clear set of environments and sub-environments, all the different areas within the ancient crater lake. We can very confidently say, if we go there and we do our job and we collect a diverse set of examples that have been very well characterized and we bring them back — if we do not find any evidence of life in there, that tells us something quite significant.
This is a clearly habitable environment early in Mars' history. If life had emerged on Mars, it seems very likely that it would've left signs in an environment like Jezero crater. If we bring back samples from Jezero crater and find no signs of life, what then?
Then there was the panoramic video , a sound recording , and deployed its Ingenuity helicopter , all in the space of a week! Shortly after the rover started drilling into the floor of the Jezero crater, Perseverance found evidence of fossilized bacteria! The search for life on Mars finally struck paydirt!
But what if it does? What will be the impact if and when it finds it? But the rover is also focused on astrobiology, which refers to the study of life throughout the Universe. As the next most-habitable place in our Solar System beyond Earth, Mars is a major focus of our astrobiological efforts.
Extraordinary claims require extraordinary evidence, and the discovery that life existed elsewhere in the universe would certainly be extraordinary. Thanks to the many rovers, orbiters, and landers that explored Mars in the past, scientists understand that billions of years ago, Mars was a much different place than it is today. Its atmosphere was denser, its climate warmer, and liquid water flowed on its surface. This led to many of the features that are observable today, like the preserved river delta in the Jezero crater.
This feature indicates that ca. This caused sediment to build up over time, leading to the formation of a river delta that is rich in clays. While the lake may be long gone, scientists theorize that there could be biosignatures somewhere in this 45 km 28 mi wide crater just waiting to be found.
The results showed it could. That will include further studies on the surface of Mars by Curiosity in regions that are more conducive to life. Sign up to our free Launchpad newsletter for a voyage across the galaxy and beyond, every Friday.
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