Did Earth's Water Come from Space?

German researchers say the chemical composition of water found on a comet could explain how Earth ended up with water.

Astronomers have discovered water on a comet that's awfully similar to the water found on Earth, leading them to believe that at least some of the water on this planet could have come from outer space. Using a telescope called the Herschel Space Observatory, researchers at the Max-Planck-Institut fur Sonnensystemforschung in Germany examined frozen water on the comet 103P/ Hartley 2, a comet that originated in the Kuiper asteroid belt on the far side of Neptune. That water was found to have a very similar ratio of hydrogen to deuterium, a heavier form of the element, to that of Earth's water, which has a very distinct ratio of the two. That the two ratios were so similar led the the research team to conclude that our water could have been transported to Earth aboard asteroids that smashed into the Earth's surface hundreds of millions of years ago.