Regional Dust Storms Enhance Martian Water Loss to Space
Individual regional dust events can boost planetary water loss by a factor of five to ten and represent an important driver of atmospheric evolution on mars, according to an analysis of data collected by a trio of spacecraft: NASA’s Mars Reconnaissance Orbiter (MRO), ESA’s Trace Gas Orbiter (TGO), NASA’s Mars Atmosphere and Volatile EvolutioN (MAVEN) orbiter.
Dust storms heat up higher altitudes of the Martian atmosphere, preventing water vapor from freezing as usual and allowing it to reach farther up.
In the higher reaches of Mars, water molecules are left vulnerable to ultraviolet radiation, which breaks them up into their lighter components of hydrogen and oxygen. Hydrogen, which is the lightest element, is easily lost to space, with oxygen either escaping or settling back to the surface.
Planetary scientists have long suspected that Mars has lost most of its water largely through this process, but they didn’t realize the significant impact of regional dust storms, which happen nearly every summer in the planet’s southern hemisphere.
Globe-enveloping dust storms that strike typically every three to four Martian years were thought to be the main culprits, along with the hot summer months in the southern hemisphere when Mars is closer to the Sun. But the Martian atmosphere also gets heated during smaller, regional dust storms.
In the new research, an international team of researchers found that Mars loses double the amount of water during a regional storm as it does during a southern summer season without regional storms.
In January-February 2019, a rare convergence of spacecraft orbits during a regional dust storm allowed the team to collect unprecedented observations.
MRO measured the temperature, dust and water-ice concentrations from the surface to about 100 km (62 miles) above it.
Looking within the same altitude range, TGO measured the concentration of water vapor and ice.
And MAVEN capped off the measurements by reporting the amount of hydrogen, which would have broken off water molecules, in the highest reaches of Mars, upwards of 1,000 km (620 miles) above the surface.
“It was the first time so many missions focused in on a single event. We’ve really caught the whole system in action,” said Dr. Michael Chaffin, a researcher in the Laboratory for Atmospheric and Space Physics at the University of Colorado at Boulder.
TGO spectrometers detected water vapor in the lower atmosphere before the dust storm began.
Typically, the temperature of the Martian atmosphere gets colder with height for much of the Martian year, which means water vapor rising in the atmosphere freezes at relatively low altitudes.
But as the dust storm took off, heating the atmosphere higher up, the instruments saw water vapor reaching higher altitudes.
These instruments found 10 times more water in the middle atmosphere after the dust storm started, which coincides precisely with data from MRO’s infrared radiometer.
The radiometer measured rising temperatures in the atmosphere as dust was raised high above Mars.
It also saw water-ice clouds disappear, as expected, since ice could no longer form in the warmer lower atmosphere.
Images from MAVEN’s ultraviolet spectrograph confirm this. They show that before the 2019 storm, ice clouds could be seen hovering above the soaring volcanoes in the Tharsis region of Mars.
“But they disappeared completely when the dust storm was in full swing and reappeared after the dust storm ended,” Dr. Chaffin said.
At higher altitudes, water vapor is expected to break down into hydrogen and oxygen by the Sun’s ultraviolet radiation.
Indeed, observations from MAVEN showed this, as it captured the upper atmosphere aglow with hydrogen that increased by 50% during the storm.
“This measurement corresponded perfectly with a swelling of water 100 km below, which was the source of the hydrogen,” the authors said.
originally by SciNews