An October 2011 report published in "Nature" states that "Herschel" measurements of deuterium levels in the comet Hartley 2 suggests that much of Earth's water could have initially come from cometary impacts. On 20 October 2011, it was reported that oceans-worth of cold water vapor had been discovered in the accretion disc of a young star. Unlike warm water vapor, previously detected near forming stars, cold water vapor would be capable of forming comets which then could bring water to inner planets, as is theorized for the origin of water on Earth.