Exciting discovery: The ESA ExoMars space probe has detected hydrogen chloride in the atmosphere of Mars for the first time. This gas is likely formed when salty dust is thrown into the Martian atmosphere during storms and reacts there. However, it is a mystery where the hydrogen chloride then disappears – apparently some unknown processes are still taking place in the Martian gas envelope, as the scientists explain in the journal “Science Advances”.
The gas envelope of the red planet has not been fully explored – on the contrary: space probes have repeatedly discovered substances and processes there that are puzzling planet researchers.
The oxygen content of the Martian atmosphere fluctuates more than known processes can explain. And the gas methane also amazes with its abrupt rise and equally rapid disappearance. Also surprising: In the high atmosphere there are even clouds of ice.
Search for hydrogen chloride
Planetary researchers working with Oleg Korablev from the Russian Space Research Institute in Moscow have now discovered another, previously unknown component of the Martian atmosphere: hydrogen chloride (Hl). This gas turns into hydrochloric acid in the presence of water, but it also occurs in small quantities in the upper atmosphere of the earth.
The re it can release chlorine radicals under UV exposure and contribute to ozone depletion.
Planetary researchers have been looking for traces of hydrogen chloride on Mars for a long time, because it could theoretically point to active volcanism. But only now have Korablev and his team detected the gas for the first time – with the help of ESA’s MarsExpress Trace Gas Orbiter (TGO). Both spectrometers on the probe detected the spectral signature of the hydrogen chloride from summer 2018 and into spring 2019.
Surprisingly widely distributed
“This is the first detection of hydrogen chloride on Mars and the first finding of a halogen gas in the Martian atmosphere,” explains co-author Kevin Olsen from the University of Oxford. His colleague Håkan Svedhem from ESA adds: “This is the first new gas class that has been determined since the discovery of methane by the ESA Mars Express probe in 2014.”
The interesting thing, however, is that the hydrogen chloride on Mars does not seem to originate from local volcanic emissions, as previously assumed. Its concentration is too high for this and the gas is distributed too evenly, as the researchers explain. In the northern hemisphere, the TGO detected one to two parts per billion (ppb) at altitudes between 15 and 25 kilometers. In the southern hemisphere it was two to three ppb at an altitude of 20 to 30 kilometers.
“This means that the concentrations of hydrogen chloride on Mars are comparable to those in the upper stratosphere and mesosphere of the earth,” the scientists explain.
The first indications are the temporal course of the spectral evidence:
The probe detected the first spectral signatures of hydrogen chloride during the global dust storm in summer 2018. “This indicates that physical or chemical processes in the Martian storms cause the gas to be released from the dust blown up”, say Korablev and his team.
Specifically, they suspect that the table salt (NaCl) and perchlorate (ClO4–) supplies the chloride for the gas. In the atmosphere there is then a reaction with water vapor, through which hydrogen chloride is generated in further steps. Exactly what reactions the chlorine-containing molecules go through in the atmosphere of the red planet has not yet been clarified.
And something else remains unexplained: After the heavy dust storms on Mars, the hydrogen chloride disappeared surprisingly quickly – faster than current models allow. “This loss indicates an unexpected chemical sink for this gas,” the researchers state. “
The temporary nature of the hydrogen chloride tells us that we don’t see the full picture here – and that we are missing an important breakdown process for the chloride.”
According to Korablev and his colleagues, their discovery demonstrates how sketchy our knowledge of the Red Planet’s atmosphere and its chemistry still is.
The evidence of hydrogen chloride and its mysterious disappearance suggest previously unknown interactions between the surface and the atmosphere. “Now we need to understand this chemical cycle,” says Olsen.
The researchers now want to carry out laboratory tests and model simulations to reconstruct the possible processes in the Martian atmosphere. But the further monitoring of the Martian hydrogen chloride with the help of the Trace Gas Orbiter should help to better understand the temporal and spatial relationships. (Science Advances, 2021; doi: 10.1126 / sciadv.abe4386)
Natasha Kumar has been a reporter on the news desk since 2018. Before that she wrote about young adolescence and family dynamics for Styles and was the legal affairs correspondent for the Metro desk. Before joining The Times Hub, Natasha Kumar worked as a staff writer at the Village Voice and a freelancer for Newsday, The Wall Street Journal, GQ and Mirabella. To get in touch, contact me through my email@example.com 1-800-268-7116