Here’s a story: many millions, perhaps billions, of years ago an asteroid impacted a distant planet and left a giant crater on its already quite cratered face. Slowly, gradually, wind filled the crater with sediments, layer by layer, until the enormous bowl was brimming over. Then, wind erosion scoured the crater’s interior and carved away the sediments layers into a mountainous heap that rose from the center like a pimple. Then the crater filled again with more sediment. And again wind erosion carved the layers away. Millions of years had passed. The mountain grew taller. Finally, a last layer of sediment was carried into the crater by water, forming deposits around the base of the mountain in the shape of a fan—or maybe the fan-shaped deposits were there before the second episode of wind erosion. Or before the first. Maybe there was never any water at all.
To be honest, it was all very confusing to the aliens living on the next planet over, so a bunch of really smart ones built a robot and sent it to the crater to get to the bottom of everything. Inside the robot was a complex miniature laboratory, where chemical tests could be run on the sediment to see what had really happened in the crater, and to see if water had ever been present. Or life. The robot looked like this:
NASA’s Curiosity rover landed on the surface of Mars at approximately 1:30AM EST on August 6th, 2012. In a marvel of engineering, NASA scientists designed a landing procedure that brought the rover safely to the planet’s surface, seven minutes after breaking into the atmosphere at a speed of 13,000mph. Late Sunday night, the scientists waited through these grueling seven minutes at the Jet Propulsion Laboratory in Los Angeles.
"Touchdown confirmed," the dispatcher said at last, as cheers erupted. "We're safe on Mars. Time to see where our curiosity will take us."