LIFE ON EARTH WITHOUT MOON

— Earth's moon helped stabilize the planet's tilt, making its climate suitable for advanced life.

— Without a moon, life on Earth probably would have flourished as well, since Jupiter and other factors exert a steadying hand.

— The research has implications for understanding if planets in habitable zones are indeed suitable for life.

Scientists have long believed that without the moon's stabilizing gravitational influence, variations in Earth's tilt would have caused climate change too dynamic for complex life to evolve. Not so, concludes a new study that has implications for understanding conditions for life elsewhere in the solar system.

The study sprang from the ongoing Kepler Telescope mission to find Earth-like planets circling in habitable zones around other stars in the Milky Way.

"We were wondering 'Do we really have to find a moon or not?' around potentially habitable worlds, planetary scientist Jason Barnes, with the University of Idaho, told Discovery News.

Previous studies showed that without the steadying gravitational influence of a large moon, Earth's tilt would shift by as much as about 85 degrees every 100,000 years or so, alternatively freezing and baking the planet's poles. Scientists believe a stable climate spanning about 500,000 years was necessary for complex life to blossom on Earth.

A new computational analysis, however, shows that a moonless Earth would still have swings in its tilt but the influence of Jupiter and other factors would limit the variations to about 10 degrees in either direction.

Earth's rotational tilt varies between 0.5 and 1 degree about every 100,000 years.

"Plus- or minus-10 would certainly be noticeable and may be a problem, but I don't think it would prevent life from coming about," Barnes said.