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Researchers at the University of Colorado, Boulder Laboratory for Atmospheric and Space Physics (LASP) have discovered an atmospheric escape route for hydrogen on Mars, a mechanism that may have played a significant role in the planet’s loss of liquid water.

The findings describe a process in which water molecules rise to the middle layers of the planet’s atmosphere during warmer seasons of the year and then break apart, triggering a large increase in the rate of hydrogen escape from the atmosphere to space in a span of just weeks.

The study, which appears in the journal Nature Geoscience, cuts against traditional models that have historically considered Martian hydrogen escape to be slower and more constant.

“Going back to the 1970s, the conventional picture of Martian hydrogen loss has been one of slow, steady escape over long time scales,” said Mike Chaffin, a research associate at LASP and lead author of the new study. “With this work, we find that there are ways to produce much more seasonal variation than previously thought.”

Atmospheric loss has controlled Mars’s habitability over time, removing most of the planet’s liquid water through the escape of atomic hydrogen and oxygen to space. In 2007, observations from NASA’s Hubble Telescope and the European Space Agency’s Mars Express spacecraft first noticed large seasonal variations in the planet’s rate of hydrogen escape. When Mars’s orbit brings it closest to the sun, hydrogen escape increases by a factor of up to 100.

“This seems to happen every Martian year. We see efficient escape while the planet is close to the sun and less escape when it’s further away,” said Chaffin. “That tells us that the old explanation for Martian hydrogen escape is insufficient.”

The full press release is available at the University of Colorado, Boulder LASP website.

The photochemical modeling for the research was supported by the NASA Earth and Space Science Fellowship (NESSF) Program, the NASA Mars Data Analysis Program (MDAP), and the NASA Astrobiology Institute Early Career Collaboration Award.