Mars’ lost water: partly stripped to space, mostly trapped underground
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Mars’ vanished water, once thought lost entirely to space, now appears split between two fates: some blown away by the solar wind and a substantial portion trapped kilometres deep in the planet’s crust, according to recent analyses. The solar wind continues to strip atmosphere today at a rate of 100 grams per second, while seismic data from NASA’s InSight lander reveal a potential vast underground reservoir. The dual picture resolves a decades-old planetary mystery.
Atmospheric Escape
Mars’ global magnetic field collapsed around 4 billion years ago, leaving the planet exposed to the solar wind. NASA’s MAVEN orbiter measures current atmospheric loss at roughly 100 grams per second, with rates spiking during solar storms. New observations from MAVEN and China’s Tianwen-1 reveal that giant plasma waves on the dayside concentrate the stripping process, forming dense clouds of planetary particles carried into space. Over billions of years, this mechanism likely removed an ocean’s equivalent of water.
Subterranean Reservoir
A 2024 study in the Proceedings of the National Academy of Sciences, led by Vashan Wright, Michael Manga, and Matthias Morzfeld, reanalyzed seismic data from the InSight lander. The results indicate that vast amounts of water may be trapped in fractures and pores of the Martian crust at depths of 11–20 km. If the crust is uniformly saturated, the subsurface could hold a global equivalent water layer hundreds of metres deep. This finding challenges the earlier consensus that almost all water escaped to space.
What's Next
NASA’s Perseverance rover continues to sample Jezero Crater’s river delta, but whether future missions will drill deep enough to confirm the underground water remains an open question. Scientists caution that the exact ratio of water lost to space versus trapped underground is still uncertain and requires more refined models of the planet’s interior.
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Mars’ lost water: partly stripped to space, mostly trapped underground
