Mars once rippled with rivers and ponds billions of years ago, providing a potential habitat for microbial life. As the planet’s atmosphere thinned over time, that water evaporated, leaving the frozen desert world that NASA’s Mars Reconnaissance Orbiter (MRO) studies today.

It’s commonly believed that Mars’ water evaporated about 3 billion years ago. But two scientists studying data that MRO has accumulated at Mars over the last 15 years have found evidence that reduces that timeline significantly: Their research reveals signs of liquid water on the Red Planet as recently as 2 billion to 2.5 billion years ago, meaning water flowed there about a billion years longer than previous estimates.