The eyes of the TGO spacecraft sift through the Martian atmosphere

Details: Published: 11 April 2019

cs nature Two articles just published in the journal Nature report the first scientific results obtained by the instruments on board the Trace Gas Orbiter (TGO), the probe of the ExoMars mission in orbit around Mars. The data collected is the result of the analysis of an international team that sees the participation of INGV, INAF and ASI
The search for methane in the atmosphere of the Red Planet and the analysis of suspended dust are the main topics of the investigations carried out by a team of researchers from the National Institute of Geophysics and Volcanology (INGV), the National Institute of Astrophysics (INAF) and the Italian Space Agency (ASI).
The mission of the European Space Agency (ESA) and RosCosmos ExoMars used instruments that see a fundamental Italian contribution, both from a scientific point of view and from a technological and industrial point of view, with Thales Alenia Space Italia leading the design of both ExoMars missions and the strong support provided by ASI.
"The TGO probe", explain Giancarlo Bellucci and Giuseppe Etiope, the two Italian researchers from INAF and INGV who collaborated on the study, "through the two high-precision spectrometers NOMAD and ACS, sounded the atmosphere of Mars at various latitudes from April to August 2018, not detecting methane in this space-time band. However, the gas could exist at concentrations lower than those detectable by instruments (0.05 parts per billion by volume, or ppbv).”
This result is only apparently in contrast with the previous measurements of methane carried out through terrestrial telescopes, the NASA Curiosity rover and, recently, through the European Mars Express probe, and opens up new interpretations since, on the basis of current knowledge, methane, a once released into the atmosphere of Mars, it should spread rapidly everywhere, persisting for a few hundred years.
“In particular”, continues Giancarlo Bellucci of INAF, “methane on Mars seems to appear and disappear quickly, suggesting the presence of a destruction mechanism capable of efficiently removing this gas from the atmosphere. Several mechanisms have already been proposed and some of these seem to be able to explain the observed spatio-temporal variations. However, these are still preliminary results of simulations or experiments performed in the laboratory on limited samples, whose validity and statistical importance will have to be demonstrated by further studies".
Some researchers consider the variability of the presence of methane in the Martian atmosphere plausible.
“Methane”, explains Giuseppe Etiope of INGV, “could be produced within the planet and its migration and release into the atmosphere could only take place in certain areas, geologically suitable, especially where there are faults and fractures in the rocks. We have already verified in previous studies that, as on Earth, this gas leakage from the rocks can be episodic and sporadic. This would partly explain the methane variations observed so far. However, the hypothesis of the rapid removal of gas from the atmosphere remains: this is the aspect to be discovered in the near future. However, the TGO probe does not detect methane in concentrations below 0.05 ppbv. With this limit it is still possible to have local methane emissions, similar to some observed on Earth, which, once diluted in the Martian atmosphere, would give rise to a low background concentration. Methane could therefore only be detected near the emission zone and in a period not too far from the release event".
Furthermore, in order to analyze the suspended dust, the two spectrometers on board the TGO spacecraft made the first high-resolution measurements of the Martian atmosphere during a sandstorm with the solar occultation method, i.e. observing how the sunlight it is absorbed into the atmosphere, thus revealing the chemical composition of its constituents.
“The measurement of the vertical profile of the water in global dust storm conditions allowed us to determine the effects of atmospheric warming on the distribution of water vapour”, explains Giancarlo Bellucci. “Under normal conditions, in fact, water vapor condenses below 40 km. However, due to the global storm, the atmosphere warms up and water vapor can migrate to higher altitudes. This mechanism was predicted by atmospheric circulation models but this is the first time it has been observed. Furthermore, the TGO probe has also measured for the first time the vertical distribution of a water isotope, important for understanding the history of water on Mars”.
This made it possible to reconstruct the vertical distribution of water vapor and semi-heavy water (in which one of the two hydrogen atoms is replaced by a deuterium atom, a form of hydrogen with an additional neutron) from near the Martian surface to over 80 km high. The new results highlight the effect of atmospheric dust on water vapour, as well as the loss of hydrogen atoms into space.
“At northern latitudes,” concludes Ann Carine Vandaele, of the Royal Belgian Institute for Space Aeronomy (BIRA-IASB) and NOMAD principal investigator, “we observed dust clouds at altitudes of about 25-40 km that had not previously been detected , while in the southern latitudes we have seen layers of dust moving to higher altitudes”.