Wired: Two US astronomers have proposed that our solar system’s asteroid belt may have been necessary for life to develop on Earth. Rebecca Martin of the University of Colorado Boulder and Mario Livio of the Space Telescope Science Institute in Baltimore have hypothesized that asteroid belts tend to form near the snow line, the region of space far enough from the Sun for hydrogen compounds to condense into solid ice grains. Gravitational forces between the Sun and giant planets such as Jupiter could have kept the grains from consolidating into planets and instead sent them hurtling into the planets in the inner solar system, including Earth. The ice grains may have drastically influenced early Earth’s climate and environment and provided the raw materials needed for life. Because of the dearth of asteroid belts in exosolar systems, there may be fewer planets that could support life than we previously thought. Martin and Livio’s paper appears in the Monthly Notices of the Royal Astronomical Society.