For the first time, scientists have seen hydrogen chloride on Mars. The source of this colorless gas is not yet clear, but current theories include volcanic activity or a previously undetected chemical cycle linked to the epic dust storms on the red planet.
New research published today in Science Advances is the first to document hydrogen chloride (HCl) and its chlorine-associated chemistry in the Martian atmosphere. This is the first detection of a new class of molecules on Mars since methane was produced, a potential biosignature. uncovered in 2004. Hydrogen chloride is not associated with life (quite the opposite, actually), but, like methane, its presence on Mars is now a question that needs an answer.
Kevin Olsen, co-author of the study and researcher in the Department of Physics at Oxford University, says there are two possibilities: either the gas is produced by magmatic activity below the surface. or through complex chemical interactions involving surface dust and atmospheric gases. What is right will be an exciting result.
“If evidence grows of the proposed chemical cycle that binds minerals to the surface dust with gases in the atmosphere, this will be the first known direct link between the surface and the atmosphere, apart from ice formation,” Olsen explained in a e-mail. “On the other hand, if it is determined that some type of ventilation is the source of HCl, such as volcanoes or other igneous gases, then this is one of the first evidence of active geological processes that has been found.”
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In fact, NASA ‘s InSight spacecraft, through its discovery of marsquakes, has suggested the presence of unknown geological processes on Mars. The aforementioned discovery of methane also points to unknown geological or possibly biological processes. However, if a chemical cycle involving surface materials and atmospheric gases were involved in HCl, this would still represent a great triumph for science. i the ExoMars Trace Gas Orbiter (TCO), as this is precisely the kind of thing it was designed to detect.
The TCO, which was used to detect HCl on Mars, is a joint mission of the European Space Agency and Russia. Roscosmos, and has been orbiting Mars since 2016. The main goal of the ExoMars project is to catalog rare gases in Mars’ lower atmosphere, such as water vapor, nitrogen dioxide, acetylene, and methane. The discovery and possible interaction of these and other compounds could provide evidence of previously undetected chemical processes. Mart. The discovery of HCl was reported, therefore, represents a slam dunk for the Trace Gas Orbiter.
Data collected by the TCO Atmospheric Chemistry Suite the spectrometer revealed a spectral sequence consistent with HCl. The team detected “multiple spectral features, a pattern of strengths and characteristic positions” that allowed them to “uniquely identify HCl,” said Oleg Korablev, a planetary scientist at the Moscow Space Research Institute and first author of ‘study. in an email. “We even recognized two isotopes with different atomic weights of Cl, 35Cl and 37Cl,” he added.
HCl, a very important gas in the Earth’s atmosphere, is invisible at room temperature, but produces white vapors of hydrochloric acid when in contact with atmospheric water vapor.
“Near the surface, it is formed from evaporated seawater and is related to the formation of acids, and at the top of the atmosphere it plays a role in the destruction of ozone,” Olsen said. “It is also emitted from volcanoes, so we have been looking for it on Mars, a sign that there is active volcanic activity. But we don’t believe volcanoes are the cause of what we’ve seen. WI think there is another atmospheric chemistry at play. ”
Olsen and colleagues suspect this because it appears that the behavior of HCl and water vapor is related. This water vapor comes from the polar ice cap, which, during the summer marching in the southern hemisphere, leaks evaporated water into the atmosphere. And, in fact, HCl was detected in April 2019, which is late summer in the southern Martian hemisphere.
“Our observations are of the effects that the seasonal freeze-thaw cycle of polar caps has on the atmosphere and climate of Mars,” Olsen said.
It is important to note that HCl signatures were also detected during a epic dust storm which enveloped the planet in 2018, the same storm every ten years as permanently knocked out NASA’s Opportunity rover. The global dust storm caused a temporary greenhouse effect, which caused water to reach from near the surface at higher altitudes. These were the conditions, “a warm, dusty, humid atmosphere,” that may have led to the formation of HCl on Mars, Olsen said. But, as scientists observed over the next year, HCl formation “can occur under regular, seasonal dust conditions,” he noted..
At the same time, evidence of a volcanic origin of HCl remains weak. Other volcanic gases “expected to be more abundant”, such as sulfur dioxide, “They are not detected on Mars,” Korablev said. “The distribution of our detections on the planet does not support any local source around which HCl is concentrated,” while NASA’s InSight land “found that seismic activity on Mars is low.” According to him, all these facts “are at odds with the volcanic origin of HCl.”
It is rare, however, for HCl to disappear rapidly. It was seen during and after the global dust storm and also during the dust season, but then it has disappeared and researchers do not know why.
“Our understanding of how HCl behaves doesn’t explain it,” Olsen said. “It won’t condense or freeze like carbon dioxide or water, it shouldn’t break so quickly and there’s too much to move to a place where our instruments don’t measure. We hope there are interactions with solid dust and ice particles, but how HCl can be removed from the atmosphere as quickly as we see it is a mystery, ”he said.
That HCl exists on Mars is not a big surprise, as perchlorates (a different chlorine compound), Found in 2008, it hinted at the presence of this gas. If researchers are right about a chemical source of HCl and whether chlorine circulates between the mineral and gaseous phases, “this will have an impact on perchlorate formation, but we have yet to see to what extent,” Olsen said. To this he added: “HCl is also very reactive and plays an important role in the Earth’s atmosphere and we see it at much higher levels than expected, so it will affect our way of seeing and modeling the chemistry of the Martian atmosphere “.
Now the team is looking forward to exploring the TCO data collected during the next Martian year, when no global dust storm appeared. The team will study how the appearance and disappearance of HCl is related to dust and atmospheric vapor. and the potential ingredients involved in the proposed gas-mineral reaction. At the same time, the team also expects “new developments in the modeling of atmospheric chemistry and laboratory studies related to chlorine chemistry on Mars,” Korablev said.
We like to think of Mars as the next best thing for Earth, but studies like this remind us of the inhospitable and alienation of this place. There is a very funny chemistry that has no clear analogies to the processes seen on Earth. Mars, with no water flowing to the surface, a painfully fine atmosphere full of carbon dioxide and highly fluctuating temperatures, is home to exotic processes that are hard for us to understand. Suffice it to say: we will not live there very soon.