Astronomers have determined the isotopic composition of water in the atmosphere of Mars to understand why large bodies of water have evaporated from the planet.
Planetologists under the leadership of Juan Aldai from Oxford University during one Martian year, about 687 Earth days, observed changes in the concentration of vapors of ordinary and heavy water in different layers of the planet’s atmosphere.
Further, the authors determined how the fractions of deuterium and hydrogen in the atmosphere fluctuated in different seasons, and also found out when water molecules got into those regions of the atmosphere from where they could get into space.
Our data show that most often the molecules of ordinary and heavy water are destroyed in the atmosphere of Mars and escaped into space at the moment when the planet comes closest to the Sun. When Mars is at the maximum distance from the star, this does not happen.
This was due to the fact that water vapor can escape from the atmosphere of Mars only if they rise to a sufficiently large distance, about 40-60 km from the surface of the planet, where they will be decomposed by rays of light.
If water molecules disintegrate at a low altitude, then their remnants have time to combine with other substances before they reach the boundary of space.
The authors continue their research and hope to restore the view of Mars before most of the water disappeared from it.