Many of us see a man in the moon—a human face smiling down at us from the lunar surface. The "face," of course, is just an illusion, shaped by the dark splotches of lunar maria (smooth plains formed from the lava of ancient volcanic eruptions). Like a loyal friend, the man is always there, constantly gazing at us as the moon revolves around Earth. But why did the moon settle into an orbit with the man facing Earth?

Saturn's largest moon, Titan, is an intriguing, alien world that's covered in a thick atmosphere with abundant methane. Titan boasts methane clouds and fog, as well as rainstorms and plentiful lakes of liquid methane. The origins of many of these features, however, remain puzzling to scientists. Now, Caltech researchers have developed a computer model of Titan's atmosphere and methane cycle that, for the first time, explains many of these phenomena in a relatively simple and coherent way.

The best place to look for signs of past life on Mars may be underground. According to a new interpretation of the distribution of clay minerals on Mars, warm water may have stayed mostly confined to the planet's subsurface for hundreds of millions of years.

Researchers at the Caltech have directly determined the surface temperature of early Mars for the first time, providing evidence that's consistent with a warmer and wetter Martian past.