Mars Might Have Lost its Water Quickly

Mars is an arid place, and aside from a tiny amount of water vapour in the atmosphere, all water exists as ice. But it wasn’t always this arid. Evidence of the planet’s past wet chapter dots the surface. Paleolakes like Jezero Crater, soon to be explored by NASA’s Perseverance Rover, provide stark evidence of Mars’ ancient past. But what happened to all that water?

It disappeared into space, of course. But when? And how quickly?

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There Might Be Water On All Rocky Planets

Artist’s impression of a massive asteroid belt in orbit around a star. Earth's water may not have all come from asteroids and comets, so maybe that's true for exoplanets. Credit: NASA-JPL / Caltech / T. Pyle (SSC)

If you asked someone who was reasonably scientifically literate how Earth got its water, they’d likely tell you it came from asteroids—or maybe comets and planetesimals, too—that crashed into our planet in its early days. There’s detail, nuance, and uncertainty around that idea, but it’s widely believed to be the most likely reason that Earth has so much water.

But a new explanation for Earth’s water is emerging. It says that the water comes along for the ride when Earth formed out of the solar nebula.

If that’s correct, it means that most rocky planets might have water for at least a portion of their lives.

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