Dust storms play a significant role in drying out the Red Planet

It was the first time that so many missions had focused on a single event.

The atmosphere on Mars is much thinner than Earth’s atmosphere. Still, it generates winds. When these winds pick up the fine, dry dust particles on Mars, a dust storm can occur.

Scientists believed that Mars was once warm and wet like Earth and lost most of its water to outer space. But, how did it lost remains elusive.

Scientists at the Laboratory for Atmospheric and Space Physics (LASP) at the University of Colorado Boulder seem to found the answer. Their study indicates that dust storms can play a significant role in drying out the Red Planet.

Until now, Mars scientists believe that dust storms played a role in drying out the planet. But, due to a lack of measurements, they could not tie the whole picture together. Coincident observations from three spacecraft orbiting Mars in January and February 2019 indicated that Mars loses double the amount of water during these storms than during calmer periods.

It means a dust storm heats the atmosphere. This causes winds to catapult water vapor to much higher altitudes than usual. At these highest altitudes, Mars’ atmosphere is sparse, and water molecules are more vulnerable to ultraviolet radiation, which tears them into their lighter hydrogen and oxygen components. The lightest element, hydrogen, is then easily lost to space.

Michael Chaffin, a researcher at the Laboratory for Atmospheric and Space Physics, said, “All you have to do to lose water permanently is to lose one hydrogen atom, because then the hydrogen and oxygen can’t recombine into water. So when you’ve lost a hydrogen atom, you’ve lost a water molecule.”

The study was made possible by the simultaneous measurements from four instruments aboard the spacecraft. NASA’s Mars Reconnaissance Orbiter measured the temperature, dust, and water-ice concentrations from the surface to about 62 miles, or 100 kilometers, above it. Within the same altitude range, the European Space Agency’s Trace Gas Orbiter measured the concentration of water vapor and ice. The imaging ultraviolet spectrometer aboard NASA’s MAVEN spacecraft capped off the measurements by reporting the amount of hydrogen at the highest altitudes in Mars’ atmosphere, 620 miles (1,000 kilometers) above the planet’s surface.

hydrogen loss on Mar
Schematic of the cycle of hydrogen loss on Mars. Both the traditional loss mechanisms and the new concept of loss from dust storms are represented. Credit: Chaffin et al., 2021

Trace Gas Orbiter found ten times more water in the middle atmosphere after the dust storm started, which coincides precisely with data from the infrared radiometer on the Mars Reconnaissance Orbiter. The MAVEN observations 650 miles above the surface also concurred, showing a 50% increase of hydrogen during the storm.

Geronimo Villanueva, a Martian water expert at NASA’s Goddard Space Flight Center and co-author on Chaffin’s paper, said“This paper helps us virtually go back in time and say, ‘OK, now we have another way to lose water that will help us relate this little water we have on Mars today with the humongous amount of water we had in the past.”

“Images from MAVEN’s imaging ultraviolet spectrograph confirm that before the 2019 storm, ice clouds could be seen hovering above the soaring volcanoes in the Tharsis region of Mars. Because ice could no longer condense near the warmer surface, these clouds disappeared completely when the dust storm was in full swing and then reappeared after the dust storm ended.”

“Collectively, the data from the three spacecraft paint a clear picture of how a regional dust storm can help Martian water escape. The instruments should all tell the same story, and they do.”

“It was an honor to lead this fantastic international team and help bring this result to light. Studies like this one demonstrate the power of cross-mission and international collaboration to drive Mars science forward.”

Journal Reference:
  1. Chaffin, M.S., Kass, D.M., Aoki, S., et al. Martian water loss to space enhanced by regional dust storms. Nat Astron (2021). DOI: 10.1038/s41550-021-01425-w

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