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The Martian subsoil may have been habitable billions of years ago, even though the planet’s surface was an arid and icy desert.
Mars It likely produced enough geothermal heat in the ancient past to melt the bases of thick ice sheets, generating large amounts of potentially viable groundwater, a new study suggests.
The findings could help scientists better understand a decades-old mystery known as weak paradox of the young sun. Four billion years ago, the sun was about 30% weaker than it is today – too weak, apparently, to support a constantly hot and humid Mars. However, evidence of liquid water during that era abounds; NASA Mars rover Curiosityfor example, he has spent the last eight years exploring an ancient system of lakes and streams. Hence the paradox.
Water on Mars: The exploration and the tests
“Although greenhouse gases such as carbon dioxide and water vapor are pumped up early Martian atmosphere in computer simulations, climate models still struggle to support a long-term warm and humid Mars, “study lead author Lujendra Ojha, assistant professor at Rutgers University-New Brunswick in New Jersey, said in a statement.
“My co-authors and I propose that the feeble young sun paradox can be reconciled, at least in part, if Mars had high geothermal heat in the past,” Ojha said.
He and his colleagues investigated whether the required internal heat – generated by the radioactive decay of elements such as thorium, potassium and uranium – actually flowed during Mars’s Noachian era, which lasted from about 4.1 billion to 3 billion. , 7 billion years ago. The researchers focused their attention on the southern Martian highlands, a region that at the time likely supported vast ice sheets.
The team modeled the thickness, behavior and evolution of those ice sheets using a variety of data sets, including observations from NASA. Orbiter Mars Odyssey, which has been studying the Red Planet since 2001. Odyssey carries a gamma-ray spectrometer, which allowed scientists to map the abundance of thorium and potassium in the Martian crust.
The researchers determined that the heat flowing from the Martian mantle and crust would likely have been enough to melt the lower layers of thick ice sheets long ago, creating potentially habitable environments underground, regardless of the conditions on the planet’s surface.
Just as the Noachian surface was – mostly hot and humid or mostly cold and dry, with intermittent bursts of melting – it remains a subject of considerable debate. But it is widely accepted that Mars changed dramatically shortly after this era. The planet has lost its global magnetic field, leaving its once dense atmosphere vulnerable undress from the solar wind. Such stripping has left the Martian surface cold, dry, irradiated and seemingly uninhabitable, at least for Earth-like life.
But pockets of groundwater likely persisted, although they likely retreated to ever greater depths as the surface dried. Some of these Martian aquifers it may even have survived to the present day.
“At such depths, life could have been sustained by hydrothermal activity and water-rock reactions,” Ojha said in the same statement. “So, the subsoil could represent the longest lived habitable environment on Mars.”
The new study, which was published online today (December 2) in the journal Advances in science, could have applications beyond the Red Planet. For example, the feeble young sun paradox complicates our understanding of the emergence of life on early Earth, Ojha noted. Radiogenic heat may have played an important role in making our planet habitable a long time ago, he said.
A similar reasoning could also apply to exoplanets. For example, some alien worlds that appear to be orbiting too far from their host star to support life may actually be habitable “on their own merits, by their own generation of radioactive heat,” Ojha told Space.com.
The new findings do not completely resolve the feeble young sun paradox: “This is a partial solution at best,” Ojha said. He also pointed out that the heat flux numbers he and his team derived are somewhat uncertain, as they come from elementary abundances. The researchers would like to extrapolate backwards from actual measurements of the heat flux of the Martian subsoil, he said, but no such data is available.
NASA’s InSight Mars lander, which landed in November 2018, carries an instrument capable of gathering such information: a burrowing thermal probe dubbed “the mole,” designed to reach at least 10 feet (3 meters) underground. So far, however, Martian soil has done so thwarted the mole’s efforts, keeping the small digger stuck or just below the surface.
Mike Wall is the author of “Out there“(Grand Central Publishing, 2018; illustrated by Karl Tate), a book about the search for alien life. Follow him on Twitter @michaeldwall. Follow us on Twitter @Spacedotcom or Facebook.
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