Mars, once dotted with bodies of water, is today an arid desert where the slightest trace of humidity raises questions. For decades, scientists have sought to understand how a planet once rich in water could become a desolate landscape. Thanks to the combined efforts of the Hubble Space Telescope and NASA’s MAVEN (Mars Atmosphere and Volatile Evolution) mission, the answer is finally taking shape.
A once lush planet turned barren
The river valleys, fossilized deltas and hydrated minerals of the Martian surface bear witness to a past when water flowed abundantly. However, around three billion years ago, this vital resource began to disappear. Some of it seeped into the basement, but the rest remained an enigma for a long time.
Researchers, such as John Clarke of the Center for Space Physics at Boston University, are addressing this crucial question. They are interested in the mechanisms that caused Martian water to evaporate or escape, forever changing the history of the Red Planet.
Two paths for Martian water: underground or in space
According to experts, water on Mars followed two main paths:
- Freezing underground as ice or hydrated minerals.
- Break up into hydrogen and oxygen atoms, then escape into space.
This last phenomenon, called atmospheric escape, is at the heart of current research. Data collected by NASA missions reveal how light atoms gradually leave the Martian atmosphere, leading to continued loss of water over millennia.
Photodissociation: a key process in the Martian atmosphere
Sunlight plays a crucial role in breaking down water molecules in the Martian atmosphere into hydrogen and oxygen. These particularly light hydrogen atoms escape easily into space. In contrast, deuterium, a heavier isotope of hydrogen, escapes much more slowly.
This difference in escape velocity allowed scientists to measure the deuterium/hydrogen ratio in the atmosphere. This constantly evolving report provides a unique window into how much water Mars once had.
An unstable Martian atmosphere influenced by the Sun
The Martian atmosphere, far from being static, is subject to rapid variations in temperature and composition. Data shows that it sometimes heats up and cools down within a few hours, particularly depending on the planet’s distance from the Sun.
When Mars is closer to the Sun, water molecules rise faster, releasing more hydrogen and deuterium at high altitudes. These fluctuations directly influence the escape rates of atoms, making the Martian atmosphere more complex than imagined.
Implications for the search for extraterrestrial life
These discoveries are not limited to Mars. By studying how water disappeared on the Red Planet, researchers are gaining clues about the evolution of Earth-like planets. Mars, Earth, and Venus are in or near the habitable zone of the solar system, where liquid water can exist.
However, these three planets followed radically different evolutionary trajectories. Understanding why Mars lost its water while Earth was able to retain its oceans could inform our search for life elsewhere in the universe.
Mars, a natural laboratory to explore the planetary future
Studying the history of water on Mars is essential to understanding not only the past of this planet, but also that of other distant worlds. As future missions prepare to explore the Martian subsoil and analyze residual traces of water, each discovery brings us a little closer to answering a fundamental question: did life ever exist on March ?
Sources :
- NASA – Mars Exploration Program
- Publications of the Center for Space Physics, Boston University
- Studies on Martian isotopes published in Nature Astronomy
With this new light, Mars is no longer limited to being a sterile enigma: it becomes a key to deciphering the mysteries of the universe.
