New scientific findings indicate that a large amount of water from the Red Planet is trapped in its crust, rather than escaped into space.
Billions of years ago, according to geological evidence, abundant water flowed on Mars and gathered in basins, lakes and deep oceans. New research funded by NASA shows that a substantial amount of water – between 30 and 99% – is trapped in minerals in the planet’s crust, causing the current theory that the low gravity of the Red Planet escaped water into space.
Early Mars was thought to have enough water to cover the entire planet in an ocean about 100 to 1,500 meters deep – a volume roughly equivalent to half the Earth’s Atlantic Ocean. While some of this water has unquestionably disappeared from Mars through atmospheric escape, the new findings, published in the latest issue of Science, conclude that it does not take into account most of its water losses.
The results were presented at the 52nd Lunar and Planetary Science Conference (LPSC) by lead author and Dr. Caltech. candidate Eva Scheller with co-authors Bethany Ehlmann, professor of planetary science at Caltech and associate director at the Keck Institute for Space Studies; Yuk Yung, professor of planetary science at Caltech and principal investigator at NASA’s Jet Propulsion Laboratory; Danica Adams, a Caltech graduate student; and Renyu Hu, JPL researcher.
“Atmospheric escape does not fully explain the data we have about how much water actually existed on Mars,” Scheller said.
Using a variety of cross-mission data archived in NASA’s planetary data system (PDS), the research team integrated data from several NASA Mars Exploration Program missions and meteorite labs. Specifically, the team studied the amount of water on the red planet over time in all its forms (vapors, liquids and ice) and the chemical composition of the planet’s current atmosphere and crust, analyzing in particular the ratio of deuterium to hydrogen (D / H). .
While 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 in 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. Hydrogen more easily escapes the planet’s gravity in space much easier than its denser counterpart. For this reason, the loss of water from a planet through the upper atmosphere would leave a telltale sign on the ratio of deuterium to hydrogen in the planet’s atmosphere: there would be a very large amount of deuterium left behind.
However, the loss of water through the atmosphere alone cannot explain both the deuterium-hydrogen signal observed in the Martian atmosphere and the large amounts of water in the past. Instead, the study proposes that a combination of two mechanisms – capturing mineral water in the planet’s crust and losing water in the atmosphere – may explain the observed deuterium-hydrogen signal in the Martian atmosphere.
When water interacts with rock, chemical weather forms clays and other hydrated minerals that contain water as part of their mineral structure. This process takes place on Earth as well as on Mars. On Earth, the old crust continually melts in the mantle and forms a new crust at the edges of the plates, recycling water and other molecules back into the atmosphere through volcanism. However, Mars has no tectonic plates and therefore the “drying” of the surface, once it occurs, is permanent.
“Hydrated materials on our own planet are being recycled continuously through plate tectonics,” said Michael Meyer, chief scientist for NASA’s Mars Exploration Program at the Washington agency’s headquarters. “Because we have measurements from several spacecraft, we can see that Mars is not recycling, so water is now trapped in the crust or lost in space.”
A key goal of NASA 2020 Mars Perseverance rover mission to Mars is astrobiology, including the search for signs of ancient microbial life. The rover will characterize the geology of the planet and the climate of the past, will pave the way for human exploration of the Red Planet and will be the first mission to collect and hide the rock and Martian rule (broken rock and dust). Scheller and Ehlmann will help Perseverance rover operations collect these samples, which will be returned to Earth through the Mars Sample Return program, which will allow these hypotheses to be examined much earlier in anticipation of the determinants of climate change on Mars. Understanding the evolution of the Martian environment is an important context for understanding the results of the analysis of returned evidence, as well as for understanding how habitability changes over time on rocky planets.
The research and findings presented in the paper highlight the significant contributions of early career scientists to expanding 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 the existence of several 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 in NASA Earth and Space Science and Technology (FINESST).
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