New scientific findings indicate that a large amount of water from the red planet is trapped in the crust instead of escaping into space.
Billions of years ago, according to geological evidence, abundant water flowed across Mars and was collected in pools, lakes and deep oceans. New NASA-funded research shows that a substantial amount of its water (between 30 and 99%) is trapped in minerals in the planet’s crust, challenging the current theory that due to the low gravity of the planet red, the water escaped into space.
Mars was first believed to have enough water to have covered the entire planet in an ocean about 100 to 1,500 meters deep, a volume roughly equivalent to half the Earth’s Atlantic Ocean. Although some of this water has undeniably disappeared from Mars through atmospheric escape, the new findings, published in the latest issue of Science, conclude that it does not account for most of its water losses.
The results were presented at the 52nd Lunar and Planetary Science Conference (LPSC) by the lead author and Caltech Ph.D. candidate Eva Scheller along with co-authors Bethany Ehlmann, professor of planetary science at Caltech and associate director of the Keck Institute for Space Studies; Yuk Yung, professor of planetary science at Caltech and senior researcher at NASA’s Jet Propulsion Laboratory; Danica Adams, a Caltech graduate student; and Renyu Hu, JPL research scientist.
“The atmospheric leak doesn’t fully explain the data we have about the amount of water that once existed on Mars,” Scheller said.
Using a large amount of cross-mission data archived in NASA’s planetary data system (PDS), the research team integrated data from multiple missions from NASA’s Mars Exploration Program and meteorite lab work. Specifically, the team studied the amount of water on the red planet over time in all its forms (vapor, liquid, and ice) and the chemical composition of the planet’s current atmosphere and crust, examining in particular the ratio of deuterium to hydrogen (D / H).
Although water is made up of hydrogen and oxygen, not all hydrogen atoms are created equal. The vast majority of hydrogen atoms have only one proton within the atomic nucleus, while a small fraction (about 0.02%) exists as deuterium, or so-called “heavy” hydrogen, which has a proton and a neutron. Lighter hydrogen escapes the planet’s gravity into space much more easily than its denser counterpart. Therefore, the loss of water from a planet through the upper atmosphere would leave a telltale sign about the ratio of deuterium to hydrogen in the planet’s atmosphere: a very large amount of deuterium would remain.
However, water loss through the atmosphere alone cannot explain as much the observed signal of deuterium-hydrogen in the Martian atmosphere as the large amounts of water from the past. Instead, the study proposes that a combination of two mechanisms – the capture of mineral water in the planet’s crust and the loss of water into the atmosphere – may explain the observed deuterium-hydrogen signal. in the Martian atmosphere.
When water interacts with rocks, chemical weathering forms clays and other hydrated minerals that contain water as part of their mineral structure. This process occurs on both Earth and Mars. On Earth, the old crust continually melts into the mantle and forms new crust at the edges of the plates, recycling water and other molecules back into the atmosphere through volcanism. Mars, however, has no tectonic plates and therefore the “drying” of the surface, once it occurs, is permanent.
“Hydrated materials from our own planet are being recycled continuously through plate tectonics,” said Michael Meyer, chief scientist for NASA’s Mars Exploration Program at the agency’s headquarters in Washington. “Because we have measurements from various spacecraft, we can see that Mars is not being recycled and therefore water is locked in the crust or lost in space.”
A key goal of NASA’s Mars 2020 Rover Perseverance mission to Mars is astrobiology, including the search for signs of ancient microbial life. The rover will characterize the planet’s past geology and climate, pave the way for human exploration of the red planet, and be the first mission to collect and hide rock and Martian regolith (broken rock and dust). Scheller and Ehlmann will assist in the operations of the Perseverance rover to collect these samples that will be returned to Earth through the Mars Sample Return program, which will allow the most anticipated exploration of these hypotheses about the engines of climate change on Mars. Understanding the evolution of the Martian environment is an important context for understanding the results of analyzes of returned samples, as well as for understanding how habitability changes over time on rocky planets.
The research and findings outlined in the paper highlight the significant contributions of first-degree scientists in broadening our understanding of the solar system. Similarly, the research, which was based on data from meteorites, telescopes, satellite observations and samples analyzed by rovers on Mars, illustrates the importance of having multiple ways to probe the red planet.
This work was supported by a NASA Habitable Worlds Award, a NASA Science and Space Science Fellowship (NESSF) Award, and a NASA Future Investigator Award in NASA Earth and Space Science and Technology (FINESST).
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