Today, Mars is a frigid desert. But dried up deltas and riverbanks reveal that water once flowed over the plant’s surface. Where did it all go? Scientists have been trying to answer this question for decades, hoping to understand how Mars became an arid wasteland while its neighbor, Earth, kept hold of its water and became a biological paradise.

Now, by plugging observations of the red planet into new models, a team of geologists and atmospheric scientists has come up with a new picture of Mars’s past: Much of the planet’s ancient water could have been trapped within minerals in the crust, where it remains to this day.

Prior research suggested that most of Mars’s water escaped into space as its atmosphere