Mars is much more arid than even the driest deserts on Earth. But that hasn’t always been the case. Rivers once flowed there, filling lakes and perhaps even a giant ocean. And the Perseverance rover is tooling along inside one of those ancient water features. It’s in a crater that once held a large lake, fed by a river that poured through the crater’s rim.

Jezero Crater is about 30 miles wide. It formed when a giant asteroid slammed into Mars about four billion years ago.

Perseverance has found evidence of long wet periods, with long dry periods between. The rover has revealed layers of sediments deposited by water over hundreds of millions of years. It’s also found minerals that formed in a watery environment. And it’s found big boulders that were carried by a massive river.

The evidence shows that the first river flowed through Jezero a few hundred million years after the crater formed. Later, water filled the crater, forming a lake about 20 miles wide and maybe a hundred feet deep. And later still, a massive river punched through the crater’s rim. It deposited huge amounts of sediments, forming a large, thick delta. Eventually, though, the crater dried out – a dry remnant of a watery past.

Look for Mars below the Moon as they climb into good view, after midnight. The planet looks like a bright orange star. The true stars Pollux and Castor – the twins of Gemini – line up to the left of the Moon.

Script by Damond Benningfield