Who needs a moon?

Science : There may be 10 times as many extrasolar planets suitable for advanced life as previously thought, writes Govert Schilling for Science. A new study by Jack Lissauer of NASA’s Ames Research Center in California and colleagues contradicts the notion that a terrestrial planet needs a large moon to stabilize the orientation of its axis and therefore its climate. The axial tilt of Mars, which has only two tiny moons, has varied between 10° and 60° in the past, which caused a tremendous variation in climate. However, Lissauer’s study demonstrates that such climate variations would take place over billions of years—giving life plenty of time to evolve.