Since Mars Spirit and Opportunity first set down on Mars in 2004, there has been a continuous robotic presence on the Red Planet. The Phoenix and Insight Landers have answered specific questions about Mars composition and interior, while a small herd of rovers have explored terrains that appear to have once been awash in water.
While NASA’s current major focus is the Artemis program and the return of humans to the lunar surface, this work is all being done with a look ahead toward future human-missions to Mars and asteroids. The desire to go to Mars is complex and brings together all our sci-fi desires to be a multi-planet species with all our scientific desires to get to walk on the surface of another world and explore for signs of ancient life.
My hope, and the hope of other researchers, to find signs of ancient life rests in our understanding that Mars had vast oceans at about the same time that life is known to have started here on Earth.
The question becomes, does Mars still have liquid water. We know it can’t have any at the surface. The current pressure and temperature at Mars surface is such that water can exist as ice, and it can exist as gas, but liquid would pretty instantly transform to gas. There is some evidence that maybe super salty water exists near the surface and periodically wets the soil, but this isn’t the kind of water that is going to allow liquid loving life to thrive.
But what about deeper?
The InSight lander spent four years measuring quakes from its location near Mars’ equator. These quakes were generated by small asteroid impacts, quakes, and other events. As seismic waves from all these sources move through Mars’ interior, the waves can bend, and their speeds can vary as they pass through regions of varying density. Measurements of how all those seismic waves were affected by Mars interior allowed scientists to map out what’s inside Mars.
In a new study presented in the Proceedings of the National Academy of Sciences, researchers led by Vashan Wright present a new analysis of the Insight data that seems to trace out the presence of rock saturated with liquid water at depths of 11.5 to 20 kilometers.
The amount of water detected is sufficient to cover the entire planet in water to a depth of 1-2 kilometers. This indicates that past oceans may have filtered down through the Martian surface to saturate the rocks lower down in the planet’s crust.
Unfortunately, this research found the rocks closer to the surface are dry, and it may be that Mars only has accessible water, in the form of ice, at its polar ice caps.
According to co author Michael Manga, “Establishing that there is a big reservoir of liquid water provides some window into what the climate was like or could be like. And water is necessary for life as we know it. I don’t see why [the underground reservoir] is not a habitable environment. It’s certainly true on Earth — deep, deep mines host life, the bottom of the ocean hosts life. We haven’t found any evidence for life on Mars, but at least we have identified a place that should, in principle, be able to sustain life.”
To be clear, there is no expectation of little green men living 15 kilometers below the Martian surface. It is merely possible that small not-intelligent life, like bacteria and microbes, might exist in the Martian crust, just as we find life in the rock of deep mines here on Earth.
Sadly, it is looking more and more like any attempts to find life on other worlds in our Solar System is going to require significant mining equipment that we can sterilize. From kilometer thick ice shells protecting oceans on moons of Saturn and Jupiter, to kilometers of rock protecting water rich rock on Mars, water is staying tucked away. Given we don’t have the ability to sterilize stuff very well at the moment, this may be for the best. I don’t think any of us want to either kill all life on Mars with our own germs or have it kill all of us because we are bad at quarantining samples.
Fossil Hunting in Mars Samples
While looking for life living deep in the subsurface water of Mars is both a bad idea and not technologically possible at the moment, we do have other life hunting options.
The Perseverance Rover has been collecting rock samples and drilling cores as it travels through Jezero Crater and its former river delta. Since February 2021, this rover has collected 22 rock cores as it traveled roughly 30 km. Among these samples are 7 samples from along the front edge of the river deltas fan-like structure. These samples appear to be made of layered sedimentary rock that was built up during Mars wet past. According to study lead Tanja Bosak, “These rocks confirm the presence, at least temporarily, of habitable environments on Mars. …We found lots of minerals like carbonates, which are what make reefs on Earth, and it’s really an ideal material that can preserve fossils of microbial life.”
This work is published in AGU Advances.
Unfortunately, Percy wasn’t designed to detect organic molecules with certainty. Some of its instruments, like SHERLOC, have the ability to look at how ultraviolet light interacts with the minerals and while this can identify rocks that could contain organics – and it has identified rocks that could contain organics – it is also possible that these are other kinds of molecules that just happen to behave the same way.
Ultimately, we need to get all of Percy’s rock samples back to Earth where we can study them in large and well equipped labs that are both larger and require more power than we have the ability to send to Mars at this time. While a Mars Sample Return mission is planned, its timeline is uncertain and I’m not sure anyone would be surprised if humans made it to Mars before a Mars Sample Return mission can be realized.
As we learn more about the future of Mars Sample Return and other missions, we’ll bring it to you here on EVSN.