An article published in the “Journal of Geophysical Research: Planets” and one published in the journal “Icarus” report two studies that offer new information on the processes of water loss on the planet Mars. Two teams of researchers led respectively by Anna Fedorova of the Russian Academy of Sciences and Jean-Yves Chaufray of the French Laboratoire Atmospheres Observations Spatiales mainly used observations conducted with ESA’s Mars Express space probe’s SPICAM instrument together with data collected from other space probes to study the Martian atmosphere. The conclusion is that seasonal cycles and dust storms are the main causes of the dispersion of water in space. However, some of the water on Mars may still be present in the subsoil as well as in the polar ice caps.
Today on Mars there’s only a part of the water that a few billions of years ago helped to make it similar to Earth. The geological traces of the presence of that water are still visible, and many scientists investigated to understand where it ended up. One part is still present in the polar caps, another part is underground but it’s difficult to assess its amount. The space probes orbiting the red planet have been collecting data for years to understand how most of the Martian water has dispersed into space, a process that still continues today.
The Mars Express space probe’s SPICAM (Spectroscopy for the Investigation of the Characteristics of the Atmosphere of Mars) instrument is among the ones that are collecting data useful for reconstructing the processes related to water in the Martian atmosphere. At the very low pressure of that thin atmosphere, water is in a gaseous state and reaches altitudes that depend on certain conditions.
Anna Fedorova’s team found that water remains at an altitude of less than 60 kilometers when Mars is far from the Sun while it reaches up to 90 kilometers when Mars is in the part of its orbit closest to the Sun. Even at over 200 million kilometers, the Sun can prevent water from freezing at certain altitudes, and this makes the upper atmosphere saturated with moisture. This explains why the dispersion of water in space is greater in that season.
Analysis of the data also shows that dust storms contribute to water dispersion by pushing it to higher altitudes. This confirms the conclusions of another research on this topic published in the journal “Science” in November 2020.
The team led by Jean-Yves Chaufray also investigated the role of dust storms by modeling the density of hydrogen atoms in Mars’s upper atmosphere over the course of two Martian years. The model was compared with the data collected with the SPICAM instrument and the result is that in the dust storm seasons, the presence of hydrogen was underestimated. Hydrogen in the atmosphere is generally combined with oxygen to form water and this shows once again how dust storms push water into the upper layers.
These researches are showing with increasing precision how Martian water gets dispersed in space. Since 2018, the Trace Gas Orbiter (TGO) space probe of ESA and Roscosmos has also been studying the Martian atmosphere, and the data collected so far also suggests a link between water dispersion and seasonal changes. In short, different processes contribute to that loss.
Nonetheless, water dispersion calculations can only explain the loss of some of the water on Mars. Even adding the water present in the polar caps, the total is much less than the amount suggested by the geological traces. Probably, a lot of water is still present underground. In some cases, its presence has been detected, but carrying out surveys on an entire planet is a very long job. Recently, new space probes reached the red planet, so new discoveries wouldn’t be surprising.
