Mars water loss shaped by seasons and storms

Written by Copernical Team Sunday, 21 March 2021 10:00

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Mars has lost most of its once plentiful water, with small amounts remaining in the planet’s atmosphere. ESA’s Mars Express now reveals more about where this water has gone, showing that its escape to space is accelerated by dust storms and the planet’s proximity to the Sun, and suggesting that some water may have retreated underground.

This finding is supported by research led by Jean-Yves, which modelled the density of hydrogen atoms in Mars’ upper atmosphere over two years and explored how this related to water escape.

“We compared our results to SPICAM data and found good agreement – except during the dusty season, when our model underestimated just how much hydrogen was present,” says Jean-Yves. “Far more water escapes through the atmosphere during disturbed conditions than the model predicted.”

Across two martian years, one of which experienced a dust storm, Jean-Yves and colleagues estimated that the rate of water loss varied by a factor of about 100, highlighting the significant effect that dust storms can have on Mars’ rates of water loss.

The findings show that Mars loses the equivalent of a global two-metre-deep layer of water every billion years. However, even accumulated over Mars’ four-billion-year history, this amount is insufficient to explain where all of Mars’ water has gone.

“A significant amount must have once existed on the planet to explain the water-created features we see,” says Jean-Yves. “As it hasn’t all been lost to space, our results suggest that either this water has moved underground, or that water escape rates were far higher in the past.”

The results from Anna, Jean-Yves and colleagues complement recent findings by the ESA-Roscosmos ExoMars Trace Gas Orbiter (TGO), which, since 2018 and alongside Mars Express, has monitored the distribution of water by altitude in Mars’ atmosphere. These findings suggested that Mars’ rate of water loss may be linked to seasonal changes.

Mars Express’ work to determine Mars’ water loss is also supported by NASA’s MAVEN (Mars Atmosphere and Volatile Evolution) mission, which is systematically measuring the chemical composition of the martian atmosphere (specifically, the levels of atomic hydrogen and deuterium, a heavy isotope of hydrogen). Such multi-mission data will help constrain not only how water is currently behaving but also the cumulative water loss over martian history – vital to figure out whether Mars’ water has gone underground or to space.