Billions of years ago, the Red Planet was much greener; according to evidence still found on the surface, abundant water flowed over Mars and formed pools, lakes and deep oceans. The question, then, is where did all that rain go?
The answer: anywhere. According to a new study from Caltech and JPL, much of Mars’ water – between 30 and 99 percent – is trapped in minerals in the planet’s crust. The research challenges the current theory that Red Planet water fled into space.
The Caltech / JPL team discovered about four billion years ago that Mars was home to enough water to cover the entire planet in an ocean about 100 to 1,500 meters deep; volume equal to half the Atlantic Ocean on Earth. However, billions of years later, the planet was as dry as it is today. Previously, scientists trying to explain what happened to the water flowing on Mars had suggested that he fled into space, suffering from the low pressure of Mars. Although some of Mars’ water left in this way, it now appears that such an escape cannot cause most of the water loss.
“Airborne escape will not fully explain the data we have for the amount of water that once existed on Mars,” said Caltech PhD candidate Eva Scheller (MS ’20), lead author of a paper on the research. published by the journal Science on March 16 and presented on the same day at the Lunar and Planetary Science Conference (LPSC). Scheller co-authors are Bethany Ehlmann, professor of planetary science and associate director for the Keck Institute for Space Studies; Yuk Yung, professor of planetary science and senior research scientist JPL; Danica Adams, Caltech graduate student; and Renyu Hu, JPL research scientist. Caltech manages JPL for NASA.
The team studied the amount of water on Mars over time in all forms (vapor, liquid, and ice) and the chemical combination of the planet’s normal atmosphere and crust through meteorites as well as the use of data provided by Mars rovers and orbiters, looking specifically at the ratio of deuterium to hydrogen (D / H).
Water is made up of hydrogen and oxygen: H2O. Not all hydrogen atoms are created equal, however. There are two stable isotopes of hydrogen. Most hydrogen atoms have just one proton inside the atomic nucleus, while a small fraction (about 0.02 percent) contains deuterium, or so-called “heavy” hydrogen, which proton and neutron in the nucleus.
The lighter weight hydrogen (also known as protium) has an easier time escaping from the depths of the planet to space than its heavier counterpart. As a result, the planet’s water would escape through the upper atmosphere leaving a signature on the ratio of deuterium to hydrogen in the planet’s atmosphere: a portion of deuterium would be left on it. back.
However, water loss alone through the atmosphere cannot explain both the deuterium observed to signal hydrogen in the Martian atmosphere and much water in the past. Instead, the study suggests that a combination of two mechanisms – mineral water capture in the planet’s crust and loss of water to the atmosphere – can explain the deuterium-to-hydrogen signal seen in the Martian atmosphere. .
When water interacts with rock, chemical weathering creates clays and other hydrous minerals in which water is part of their mineral structure. This process takes place on Earth as well as Mars. As the Earth is tectonically active, old crusts melt into the mantle and form new crusts at plate boundaries, recycling water and other molecules back into the atmosphere through volcanism. Mars, however, is largely tectonically inactive, so the “drying” of the surface, once it occurs, is permanent.
“Air evacuation clearly played a role in water loss, but conclusions from the last decade of Mars missions have revealed that this vast reservoir of old hydrated minerals that was created certainly did. reduce the amount of water available over time, “said Ehlmann.
“All of this water was captured very early, and then it didn’t cycle out,” Scheller says. The research, which relied on data from meteorites, telescopes, satellite observations, and samples surveyed by rovers on Mars, shows how important it is to have multiple ways to study the Red Planet, she says.
Ehlmann, Hu, and Yung have previously collaborated on research that attempts to understand the potential of Mars to inhabit by discovering the history of carbon, since carbon dioxide is the main component of the atmosphere. Next, the team plans to continue using isotopic and mineral composition data to determine what minerals are nitrogen and sulfur. In addition, Scheller plans to continue studying the processes by which Mars’ surface water was lost to the crust using laboratory experiments similar to Martian weather processes, as well as through seeing an old bark with the Perseverance rover. Scheller and Ehlmann will also assist in the Mars 2020 activity to collect rock samples for return to Earth that will allow researchers and colleagues to test these ideas about the causes of climate change on Mars.
###
The paper, entitled “Drying Long-term of Mars Caused by Sequestration of Ocean-scale Water of Water in the Crust,” was published in Science on March 16, 2021. This work was supported by a NASA Habitable Worlds award, a NASA Earth and Space Science Alliance (NESSF) award, and a NASA Future Explorer in NASA Earth and Space Science and Technology (FINESST) award.
Disclaimer: AAAS and EurekAlert! they are not responsible for the accuracy of press releases posted to EurekAlert! by sending institutions or for using any information through the EurekAlert system.