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Life, as we understand it on Earth, requires certain basic ingredients. Water is one of them. And for years, NASA’s succession of robotic missions have “followed the water” to Mars to learn more about the planet’s history, including whether it ever supported life.
While many scientists believe Mars was hot and humid billions of years ago before it became the frozen desert it is today, others point to the weak young sun paradox.
Four billion years ago, our sun was much weaker – about 30% weaker. It got warmer and brighter over time. If so, then ancient Mars would have been too cold and dry for water or life on its surface.
Today, Mars receives only about 43% of the concentrated sunlight the Earth receives from the sun. This means that temperatures on ancient Mars would have struggled to rise above the melting point of water ice.
But the geological features of Mars show evidence of hydrated minerals and ancient river and lake beds. This evidence indicates that Mars likely had an abundance of liquid water during the Noachian era, or between 3.7 and 4.1 billion years ago.
This contradiction between climate modeling and the geological records of Mars is the weak paradox of the young sun.
The rocky planets of our solar system – Earth, Venus, Mercury, and Mars – contain elements that create heat through radioactive decay. These elements include uranium, potassium, and thorium.
This type of heating would be enough to melt the bottom of thick layers of ice to create liquid water, even in a low sun. On Earth, this type of heating, known as geothermal heat, can be observed in subglacial lakes forming in parts of the ice cap of West Antarctica, the Canadian Arctic and Greenland.
The phenomenon of geothermal heat also explains the liquid water on a freezing Mars 4 billion years ago.
Understanding Ancient Mars
The researchers used various datasets to test their theory of geothermal heating on Mars billions of years ago. These data included the thickness of ice deposits in the southern Martian highlands and estimates of the planet’s annual surface temperature and interior-to-surface heat flow 4 billion years ago.
Through modeling, scientists discovered that the underground melting of thick ice caps would have led to an abundance of groundwater on Mars.
“Even though greenhouse gases like carbon dioxide and water vapor are pumped into the early Martian atmosphere during computer simulations, climate models are still struggling to sustain a hot and humid Mars in the long run. Said lead author of the study Lujendra Ojha, assistant professor in the Department of Earth and Planetary Sciences in the School of Arts and Sciences at Rutgers University-New Brunswick, in a statement. “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.”
Although they don’t know what happened to make Mars so inhospitable, even though it once endured a hot and humid climate, over time the red planet lost its magnetic field, much of its atmosphere was stripped. and experienced a drop in global temperature.
This means that for liquid water to have a stable presence on Mars, it would have to be below the surface.
“Regardless of the actual nature of the ancient Martian climate, the subsoil would have been the most habitable region on Mars,” the authors wrote in the study.
As water penetrated deeper into Mars, the researchers suggested, any existing life may have followed it for miles below the surface.
“At such depths, life could have been supported by hydrothermal (heating) activity and rock-water reactions,” Ojha said. “So the basement may represent the oldest habitable environment on Mars.”
This may also have been the case on early Earth.
“Much of the Earth’s microbial biomass resides in its crust, where water is readily available,” the authors wrote in the study. “Substantial biological diversity exists in the enormous volume of underground habitable environments, which can reach (more than 5 kilometers deep). Therefore, the subsoil could have been the most viable habitat for the ancient forms of simple lives on early Earth and possibly Mars. “
Currently, NASA’s Mars InSight lander is investigating the interior of Mars after it landed in 2018 (InSight is short for Interior Exploration using Seismic Investigations, Geodesy and Heat Transport.) The data the lander collects can help. researchers to learn more about how geothermal heating can impacted the habitability of Mars billions of years ago, the researchers said.
And any evidence of potential past life on Mars, like biomarkers, may be hidden beneath the surface where it has been shielded from radiation.
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