Ice in a planetary cauldron

With temperatures in excess of 800 F, Mercury is one of the last places in the solar system you’d expect to find ice. But when NASA’s Messenger spacecraft transmitted its first optical images of the closest planets to the sun, that’s exactly what scientists discovered. Mercury sits about 36 million miles from the sun, which is roughly 57 million miles closer than Earth. Nonetheless, scientists have long suspected that icy deposits may be trapped at the poles of the planet, in permanently shadowed areas inside craters. Messenger’s photos provide the proof. The images suggest that the ice was left there—most likely by a comet— relatively recently. “Understanding the age of these deposits,” says researcher Nancy Chabot, “has implications for understanding the delivery of water to all the terrestrial planets, including Earth.”