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This illustration shows NASA’s MAVEN spacecraft and the Mars limb. Credit: NASA / Goddard
By combining observations from three international spacecraft to March, scientists have been able to show that regional dust storms play a huge role in drying up the red planet.
Dust storms warm the higher altitudes of the cold Martian atmosphere, preventing water vapor from freezing as usual and allowing it to reach higher. In the higher regions of Mars, where the atmosphere is sparse, water molecules remain vulnerable to ultraviolet rays, which break them down into their lighter components of hydrogen and oxygen. Hydrogen, which is the lightest element, is easily lost in space, with oxygen escaping or rising to the surface.
“All you have to do to lose water permanently is lose hydrogen atom because then hydrogen and oxygen cannot recombine into water, ”said Michael S. Chaffin, a researcher at the Atmospheric and Space Physics Laboratory at the University of Colorado at Boulder. “So when you lost a hydrogen atom, you definitely lost a water molecule.”
Scientists have long suspected that Mars, once hot and humid like Earth, lost most of its water largely due to this process, but they failed to realize the significant impact of regional dust storms. that occur almost every summer in the southern hemisphere of the planet. The dust storms enveloping the globe that typically strike Martians every three or four years were seen as the main culprits, along with the hot summer months in the southern hemisphere when Mars is closer to the Sun.
The yellow-white cloud at the bottom center of this image is a “dust tower” from Mars – a concentrated cloud of dust that can rise tens of kilometers above the surface. The blue-white plumes are clouds of water vapor. Olympus Mons, the highest volcano in the solar system, can be seen in the upper left corner, while Valles Marineris can be seen in the lower right. Taken on November 30, 2010, the image was produced by NASA’s Mars Color Imager from Mars Reconnaissance Orbiter. Credit: NASA / JPL-Caltech / MSSS
But the Martian atmosphere also warms up during small regional dust storms, according to a new article published on August 16, 2021 in the newspaper. Nature astronomy. The researchers, an international team led by Chaffin, found that Mars loses double the amount of water during a regional storm as it does during a southern summer season without a regional storm.
“This document helps us virtually go back in time and say, ‘OK, now we have another way of losing water that will help us connect this little water that we have on Mars today with the huge amount. of water that we had in the past, “said Geronimo Villanueva, a Martian water expert at Nasa‘s Goddard Space Flight Center in Greenbelt, Maryland, and co-author of Chaffin’s article.
As water is one of the key ingredients of life as we know it, scientists are trying to figure out how long it has been on Mars and how it got lost.
Billions of years ago, Mars had a lot more water than it does today. What remains is frozen at the poles or locked in the crust. Melted, this residual water could fill a global ocean up to 30 meters deep, some scientists say.
Although scientists like Chaffin had many ideas about what was happening to water on Mars, they lacked the necessary steps to tie the whole picture together. Then, a rare convergence of spacecraft orbits during a regional dust storm from January to February 2019 allowed scientists to collect unprecedented observations.
NASA’s Mars Reconnaissance Orbiter has measured temperature, dust and water ice concentrations from the surface up to about 62 miles, or 100 kilometers, above it. Looking at the same altitude range, ESA’s (European Space Agency) Trace Gas Orbiter measured the concentration of water vapor and ice. And NASA’s Mars Atmosphere et Volatile EvolutioN, or MAVEN, spacecraft completed the measurements by reporting the amount of hydrogen that would have broken H2O molecules, in the higher parts of Mars, more than 620 miles, or 1,000 kilometers, above the surface.
It was the first time that so many missions focused on a single event, said Chaffin: “We really saw the whole system in action. “
This graph summarizes data collected from three orbiters during a regional Martian dust storm from January to February 2019. Bottom to top: The bottom panel shows dust accumulating in the atmosphere above a region of Mars; darker brown indicates higher density. The middle panel shows a corresponding increase in temperature in the atmosphere, extending about 50 kilometers above the surface; the lighter the color, the higher the temperature. The top panel shows that as the density of the dust increases, warming the atmosphere, the ice, shown in white, disappears from the area because water vapor can no longer freeze. The following panel shows three observations of the Tharsis volcano region before (left), during (middle) and after (right) the dust storm. You can see clouds of white ice covering the volcanoes of Tharsis before and after the dust storm, but not during it. The penultimate top panel shows the increase in water density in the higher elevations during the dust storm, and above that in the top panel you see a corresponding brightening (blue clear) of hydrogen at altitudes as high as 620 miles, or 1,000 kilometers, above the surface. Credit: Michael S. Chaffin
Data collected from four instruments on the three spacecraft paint a clear picture of a regional dust storm’s role in the Martian water leak, scientists report. “The instruments should all tell the same story, and they do,” said Villanueva, a member of the science team at Trace Gas Orbiter.
European orbiter spectrometers detected water vapor in the lower atmosphere before the dust storm began. Typically, the temperature of the Martian atmosphere cools with altitude for much of the Martian year, which means that the water vapor that rises in the atmosphere freezes at relatively low altitudes. . But when the dust storm took off, warming the atmosphere higher, the instruments saw water vapor reaching higher altitudes. These instruments found 10 times more water in the middle atmosphere after the dust storm began, which coincides precisely with the data from the infrared radiometer of the Mars Reconnaissance Orbiter probe.
The radiometer measured the rise in temperatures in the atmosphere as dust rose above Mars. He also saw the water and ice clouds disappear, as expected, as ice could no longer form in the warmer lower atmosphere. The images of MAVEN’s ultraviolet spectrograph confirm this; they show that before the 2019 storm, ice clouds could be seen hovering over burgeoning volcanoes in the Tharsis region on Mars. “But they completely disappeared when the dust storm was in full swing,” said Chaffin, and reappeared after the dust storm was over.
At higher altitudes, water vapor is expected to break down into hydrogen and oxygen by ultraviolet radiation from the Sun. Indeed, MAVEN’s observations have shown this, as it captured the upper atmosphere flooded with hydrogen which increased by 50% during the storm. This measurement perfectly matched a swelling of water 60 miles below, which scientists believed was the source of the hydrogen.
Reference: “Martian water loss in space reinforced by regional dust storms” by MS Chaffin, DM Kass, S. Aoki, AA Fedorova, J. Deighan, K. Connour, NG Heavens, A. Kleinböhl, SK Jain, J.-Y. Chaufray, M. Mayyasi, JT Clarke, AIF Stewart, JS Evans, MH Stevens, WE McClintock, MMJ Crismani, GM Holsclaw, F. Lefevre, DY Lo, F. Montmessin, NM Schneider, B. Jakosky, G. Villanueva, G Liuzzi, F. Daerden, IR Thomas, J.-J. Lopez-Moreno, MR Patel, G. Bellucci, B. Ristic, JT Erwin, AC Vandaele, A. Trokhimovskiy and OI Korablev, August 16, 2021, Nature astronomy.
DOI: 10.1038 / s41550-021-01425-w
This research was partially funded by the MAVEN mission. MAVEN’s principal investigator is based at the Atmospheric and Space Physics Laboratory at the University of Colorado at Boulder, and NASA Goddard manages the MAVEN project. The Mars Reconnaissance Orbiter, which also funded some of this research, is operated by Jet Propulsion Laboratory, California Institute of Technology, for NASA.
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