Dust storms may cause hydrogen loss in Mars' upper atmosphere

Over billions of years, these storms may have transformed the planet from a warm, wet world to a cold, dry one.
By Laurel Kornfeld | Jan 26, 2018
Martian dust storms, especially global ones, may be driving loss of hydrogen from the planet's upper atmosphere, according to a new study based on data collected by NASA's Mars Reconnaissance Orbiter (MRO) during the last such storm in 2007.

Air in Mars' thin atmosphere rises during global dust storms, carrying water vapor to the upper atmosphere, from where hydrogen is separated and escapes into space.

The same mechanism has been observed during regional dust storms and is believed responsible for a seasonal pattern of hydrogen loss observed in the planet's upper atmosphere.

Over long time scales, this process could be responsible for Mars' transformation from a warm, wet world to a cold, dry one.

"We found there's an increase in water vapor in the middle atmosphere in connection with dust storms. Water vapor is carried up with the same air mass rising with the dust," explained Nicholas Heavens of Hampton University of Hampton, Virginia, who is lead author of a study on the findings published in the journal Nature Astronomy.

NASA's Hubble Space Telescope and the European Space Agency's (ESA) Mars Express orbiter have both observed a connection between water vapor in Mars' middle atmosphere, between 30 and 60 miles (50 and 100 km) high, and hydrogen escape from the planet's upper atmosphere though this occurred without a dust storm.

The link between dust storms and atmosphere loss is a surprise to scientists, many of whom thought the escape of atmospheric hydrogen occurs continuously at a steady rate rather than through dramatic events such as dust storms.

They also suspected some variation in the level of hydrogen loss to be tied to the direction of the solar wind, which is composed of charged particles coming from the Sun.

However, MRO and NASA's Mars Atmosphere and Volatile Evolution (MAVEN) orbiter, which arrived at Mars in 2014 to study atmospheric escape, found patterns of hydrogen loss to be tied to Martian seasons rather than to the solar wind.

MRO's Climate Sounder instrument, which is capable of detecting dust and ice particles in Mars' atmosphere as well as changes in water levels relating to temperature variations, confirmed an increase in middle atmosphere water vapor during regional dust storms and the presence of water vapor at significantly higher atmospheric altitudes during the 2007 dust storm.

Mars' next dust storm season will start this coming summer although the storms could be limited to regional ones.

If a global dust storm does occur, MAVEN and the other orbiters will have an unprecedented chance to observe them and gain a better understanding of their effects.

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