A Mars Rover Explored a Wasteland and Found an Oasis

Millions of miles away, on the surface of Mars, inside an enormous crater, a little NASA rover is taking some pictures. The view is?quite stunning?there—miles of undisturbed cinnamon terrain scattered with pebbles and boulders, with silky dunes where the craggy bedrock doesn’t peek through. But when the rover, named Perseverance, sent the photos back home from the crater, known as Jezero, scientists saw something more.

The arrangement of the sediment? It resembled a certain familiar landscape on Earth. Those boulders? A strong current had carried them in. Jezero, scientists could now see, wasn’t always dry and desolate. It was once a lake. The Perseverance rover was roaming what used to be a delta, where a small river met calm waters. A few billion years ago, the ground beneath its tires might have been sloshing with water.

On Earth, when a river pours into a lake, it carries grains of silt with it. Over time, that sediment builds up in layers that fan out from a narrow point where the running water meets the still. Observations from previous spacecraft missions, orbiting Mars?from above, had shown something similar on the red planet’s surface, so scientists already suspected that Jezero crater, formed after a meteor impact, had been filled in with water. But they couldn’t be sure until Perseverance was there, snapping pictures like a mesmerized tourist. Here was history, the ancient ruins of Mars. The rover had looked out across the quiet terrain and observed not a barren wasteland, but a lost oasis.

The?close-up photographs?helped scientists conclude that the sediment—based on the thickness of its layers, and the way they slope—was indeed likely shaped by flowing water, not smoothed by wind or other geological processes. The researchers can even identify past weather events as transient as flash flooding: The boulders strewn across the lake bed, some estimated to weigh several tons, are embedded in the top layers of sediment, which suggests that they originated outside the crater. They must have been carried on waters strong enough to dislodge them and then take them downstream. But the environment wasn’t always so chaotic. Beneath these boulders lie layers of fine sediment, which suggests that, before the bombardment, a gentle river fed the basin.

Somewhere along the way, the climate on Mars shifted drastically, and the planet transformed into the freezing, dusty world we see today. The sound of lapping waves has been replaced by the whirring?noise?of rovers. Scientists don’t know yet exactly what happened. But the researchers working on the Perseverance mission hope to find some answers inside that crater. An ancient lake bed is a fantastic place to look for?evidence of fossilized microbes, and the Perseverance rover will spend its time on Mars collecting rock samples into tubes and storing them away so that future spacecraft missions, years from now, can bring them home to Earth.