About 4 billion years ago, Mars looked very different from today. First, its atmosphere is thicker and hotter, and liquid water flows across its surface. These include rivers, standing lakes, and even the deep ocean that covers most of the northern hemisphere. The entire earth preserves evidence of this warm, watery past in the form of lake beds, river valleys and river deltas.
For some time, scientists have been trying to answer a simple question: Where did all the water go? After Mars lost its atmosphere, did it escape into space, or did it retreat somewhere? According to the latest research by the California Institute of Technology and NASA̵
The research was led by Eva Scheller, a Ph.D. student. Candidate of California Institute of Technology (Caltech). Professor Bethany Ehlmann of California Institute of Technology (Keck) Institute of Space Research also joined her. Professor Yuk Yung, a senior research scientist at the National Aeronautics and Space Administration JPL, California Institute of Technology; Danica Adams, a graduate student at the California Institute of Technology; and Renyu Hu, a JPL research scientist.
In the past two decades, the National Aeronautics and Space Administration (NASA) and other space agencies have sent more than a dozen robot explorers to the Red Planet to describe its geology, climate, surface, atmosphere, and evolution. In the process, they learned that Mars once had enough water on its surface to cover the entire planet in the ocean at a depth of 100 to 1,500 meters (330 to 4,920 feet)-the volume equivalent to half of the Atlantic Ocean.
By 3 billion years ago, the surface water of Mars disappeared, and the landform returned to its current state (freeze-dried). Considering how much water had ever flowed there, scientists wondered how it could have completely disappeared. Until recently, scientists believed that atmospheric escape was the key. In this case, water was chemically broken down and then lost to space.
This process is called photodissociation, in which exposure to solar radiation breaks water molecules into hydrogen and oxygen. In theory, at this point, the low gravity of Mars allows it to be stripped from the atmosphere by the solar wind. Although this mechanism certainly worked, scientists have concluded that it cannot solve most of the problem of water loss on Mars.
To conduct the research, the research team analyzed data from Martian meteorites, rover, and orbiter missions to determine how the ratio of deuterium to hydrogen (D/H) changes over time. They also analyzed the composition of the atmosphere and crust of Mars today, which allowed them to limit the amount of water that exists on Mars over time.
Deuterium (also known as “heavy water”) is a stable isotope of hydrogen. Its nucleus contains both protons and neutrons, while normal hydrogen (pro) consists of a single proton surrounded by an electron. This heavier isotope accounts for only a small part (about 0.02%) of hydrogen in the known universe, and it is difficult to escape the planet’s gravity and escape into space.
Therefore, the loss of a planet’s water into space will leave a clear signal in the atmosphere in the form of higher than normal levels of deuterium. However, this is inconsistent with the ratio of deuterium to to observed in the Martian atmosphere, so why Scheller and her colleagues suggested that much water is absorbed by minerals in the planet’s crust. As Ehlmann explained in a recent Caltech press release:
“The escape of the atmosphere is obviously the cause of the loss of water, but the discovery of the last decade of the Mars mission shows that there is such a large ancient reservoir of hydrated minerals, and its formation will undoubtedly reduce water use over time.”
On the earth, flowing water weathers rocks to form clay and water-containing minerals, the mineral structure of which contains water. Due to the tectonic activity of the earth, hydrated minerals circulate endlessly between the mantle and the atmosphere (through volcanism). Clay and hydrated minerals have also been found on Mars, indicating that water once flowed there.
However, because Mars is largely structurally inert, its surface water was isolated very early and never recycled back. Therefore, permanent drying of the surface can retain the characteristics that indicate the presence of water in the past. At the same time, a large part of this water is preserved because it is absorbed below the surface.
This research not only solves the problem of how the water on Mars disappeared billions of years ago. This may also be good news for future personnel going to Mars, depending on the ice and water collected locally. Previously, co-authors Ehlmann, Huh, and Yung collaborated on research to track carbon history on Mars, because carbon dioxide is the main component of the Martian atmosphere.
In the future, the research team plans to continue to analyze isotopic and mineral composition data to determine the source of nitrogen and sulfur minerals on Mars. In addition, Scherer plans to expand research on the cause of Martian water by conducting laboratory experiments that simulate the weathering process of Mars and by observing the ancient crust in the Jezero crater. perseverance Currently exploring).
Scheller and Ehlmann will also assist in the operation of the plant. perseverance It’s time for the Rangers to collect rocks and drill samples. These will be sent back to Earth through subsequent NASA-ESA missions, where researchers will be able to inspect them. For Scheller, Ehlmann and colleagues, this will allow them to test theories about Martian climate change and its causes.
The study describing their findings was recently published in the journal sciencePublished on March 16, titled “Long-term Dryness of Mars Caused by the Volume of Marine Water in Crusts”day During the Lunar and Planetary Science Conference (LPSC).Due to COVID restrictions, this year’s meeting is virtual and will be held on March 15thday To 19day.
With the support of the NASA Livable World Award, NASA Earth and Space Science Research Fund (NESSF) Award, and NASA Earth and Space Science and Technology Award (FINESST), this research was realized.
Further reading: California Institute of Technology, Author of California Institute of Technology