Billions of years ago, the red planet was much bluer; according to evidence still found on the surface, abundant water flowed over Mars and formed pools, lakes and deep oceans. So the question is, where has all this water gone?
The answer: nowhere. According to new research from Caltech and JPL, a significant portion of the water on Mars – between 30 and 99 percent – is trapped in minerals in the earth’s crust. The research challenges the current theory that water from the Red Planet has escaped into space.
The Caltech / JPL team discovered that about four billion years ago, Mars harbored enough water to have covered the entire planet in an ocean about 100 to 1,500 meters deep; a volume roughly equivalent to half of the terrestrial Atlantic Ocean. But, a billion years later, the planet was as dry as it is today. Previously, scientists seeking to explain what happened to the water flowing on Mars had suggested that it had escaped into space, a victim of Mars’ low gravity. While water did leave Mars this way, it now appears that such an escape cannot account for most of the water loss.
“Atmospheric escape does not fully explain the data we have on how much water once existed on Mars,” says Eva Scheller (MS ’20), doctoral candidate at Caltech (MS ’20), lead author of a research article published by the journal. Science on March 16 and presented the same day at the Lunar and Planetary Science Conference (LPSC). Scheller’s co-authors are Bethany Ehlmann, professor of planetary science and associate director of the Keck Institute for Space Studies; Yuk Yung, professor of planetary science and senior researcher at JPL; Danica Adams, Caltech graduate student; and Renyu Hu, research scientist at JPL. Caltech manages JPL for NASA.
The team studied the amount of water on Mars over time in all its forms (vapor, liquid, and ice) and the chemical makeup of the planet’s current atmosphere and crust through meteorite analysis. as well as the use of data provided by the rovers and orbiters of Mars. , looking in particular at the ratio of deuterium to hydrogen (D / H).
Water is made up of hydrogen and oxygen: H2O. However, not all hydrogen atoms are created equal. There are two stable isotopes of hydrogen. The vast majority of hydrogen atoms have only one proton in the atomic nucleus, while a tiny fraction (about 0.02%) exists as deuterium, or so-called “heavy” hydrogen, which contains a proton and a neutron in the nucleus.
The lighter hydrogen (also known as protium) escapes the planet’s gravity more easily in space than its heavier counterpart. For this reason, the leakage of water from a planet via the upper atmosphere would leave a revealing signature on the ratio of deuterium to hydrogen in the planet’s atmosphere: there would remain an inordinate portion of deuterium.
However, the loss of water only through the atmosphere cannot explain both the deuterium-to-hydrogen signal observed in the Martian atmosphere and large amounts of water in the past. Instead, the study proposes that a combination of two mechanisms – the trapping of water in minerals in the planet’s crust and the loss of water to the atmosphere – may explain the deuterium-hydrogen signal. observed in the Martian atmosphere.
When water interacts with rock, chemical weathering forms clays and other hydrated minerals that contain water as part of their mineral structure. This process occurs both on Earth and on Mars. Because the Earth is tectonically active, the old crust continually melts in the mantle and forms new crust at the boundaries of the plates, recycling water and other molecules back into the atmosphere through volcanism. Mars, however, is primarily tectonically inactive, and therefore the “drying” of the surface, once it occurs, is permanent.
“Atmospheric escapes clearly played a role in the loss of water, but findings from the last decade of missions to Mars showed that there was this huge reservoir of ancient hydrated minerals whose formation certainly decreased availability. of water over time, ”explains Ehlmann.
“All that water was sequestered pretty early on, and then was never recycled,” says Scheller. The research, which relied 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, says- it.
Ehlmann, Hu and Yung have previously collaborated on research aimed at understanding the habitability of Mars by tracing the history of carbon, since carbon dioxide is the main constituent of the atmosphere. Next, the team plans to continue using the isotopic and mineral composition data to determine the fate of nitrogen and sulfur minerals. In addition, Scheller plans to continue to examine the processes by which surface water from Mars was lost to the crust using laboratory experiments that simulate Martian weathering processes, as well as observations of the old crust by the Perseverance rover. Scheller and Ehlmann will also help in Mars 2020 operations collect rock samples for return to Earth, which will allow researchers and their colleagues to test these hypotheses about the drivers of climate change on Mars.