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For decades, robotic missions have explored Mars to learn more about the geological and environmental history of the planet. Next year the Perseverance rover will join the chase and be the first mission to return samples to Earth and by the 2030s the first crewed mission is expected to take place. All of these efforts are part of an ongoing effort to find evidence of past (and possibly present) life on Mars.
According to a new study from Rutgers University-New Brunswick, the place most likely to find this evidence is several miles below the surface. It is here (they say) that water always exists in liquid form, which is likely the result of geothermal heating that melts thick layers of ice underground. This research could help resolve lingering questions like the weak young sun paradox.
The study, which was recently published in the journal Scientific advances, was headed by Lujendra Ojha, Assistant Professor in the Department of Earth and Planetary Sciences at Rutgers University. He was joined by a team of engineers and planetary scientists from Dartmouth College (Hanover, NH), Louisiana State University (Baton Rouge, LA) and the Planetary Science Institute (PSI) in Tuscon, Arizona.
One of the most lingering questions on Mars was how it could have maintained temperatures warm enough to have liquid water on its surface. In Noachian times (around 4.1 billion to 3.7 billion years ago), the Sun was much weaker and cooler than it is today. However, there are countless geological indicators on Mars that indicate the presence of rivers, lakes, and even an ocean in its northern lowlands that date from this period.
This apparent contradiction, between geological records and climate models, is something scientists call the “Faint Young Sun Paradox”. As Professor Ojha explains in a press release from Rutgers Today:
“Even though greenhouse gases like carbon dioxide and water vapor are pumped into the early Martian atmosphere in computer simulations, climate models are still struggling to sustain a hot and humid Mars in the long run.” . My co-authors and I propose that the weak young sun paradox can be reconciled, at least in part, if Mars had high geothermal heat in its past.
One possible mechanism is heat generated by the radioactive decay of elements such as uranium, thorium and potassium. On terrestrial planets like Earth, Mars, Venus, and Mercury, these elements generate enough heat inside to keep the mantle in a slimy state. They can also melt the underside of thick ice caps, leading to the formation of subglacial lakes.
On Earth, this phenomenon is believed to have led to the formation of lakes under the ice cap in West Antarctica, Greenland and the Canadian Arctic. It is likely that a similar fusion could explain the presence of liquid water on Mars 4 billion years ago, at a time when surface temperatures would have frozen.
To verify this theory, the Rutgers team looked at various datasets from Mars to see if geothermal heating would have been possible in Noachian times. What they found was that these conditions would have been common on the surface of Mars about 4 billion years ago. As the planet lost its magnetosphere and slowly saw its atmosphere break away, the drop in temperatures likely meant that liquid water was only stable at great depths.
Therefore, if life had ever emerged on Mars, it likely would have followed liquid water as it entered the subsoil. At these levels, Ojha says, conditions would have been warm enough for life to persist:
“At such depths, life could have been sustained by hydrothermal activity (heating) and rock-water reactions. Thus, the basement may represent the longest habitable environment on Mars. “
These findings support an ongoing theory among planetary scientists and astrobiologists who are currently engaged in the search for life on Mars. Since Marinate 9 the orbiter provided the first direct evidence of past water on the Red Planet – which has been confirmed repeatedly since – scientists began to speculate where this water (and any life it supported) might be found today.
In 2018, NASA’s interior exploration using the Sismic Investigations, Geodesy and Heat Transport (InSight) lander reached the surface and began to study the interior structure of Mars. The data it is accumulating could allow scientists to better understand the role of geothermal heating on the habitability of Mars during the Noachian era. It could also point the way to life on Mars today!
Further reading: Rutgers today
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