Billions of years ago, Mars had rivers and seas on its surface, but they have all disappeared since then. The planet may have been left dry after its crust irreversibly sucked up most of that ancient water.

Many studies have suggested that Mars lost its water at the same time as it lost its atmosphere, via the water evaporating and escaping into space . However, that mechanism can’t account for water loss on the scale that is theorised to have occurred on Mars.

Eva Scheller at the California Institute of Technology and her colleagues compared simulations of the water loss process with observations from NASA’s Curiosity rover and analyses of meteorites from Mars to try to figure out what happened to the rest of the Red Planet’s water. Scheller presented this work at the virtual Lunar and Planetary Science Conference on 16 March.

In Scheller and her team’s model, Mars started off with enough water to cover the entire surface in an ocean at least 100 metres deep and became as arid as it is now by about 3 billion years ago. In simulations that matched observations of Mars, between 30 per cent and 99 per cent of that water was sucked up by the planet’s crust and incorporated into the molecular structure of minerals, not lost to space.

Journal reference: Science , DOI: 10.1126/science.abc7717