The Herschel Space Observatory reveals that comet Hartley 2, a comet from the Kuiper Belt, is largely composed of water with the same composition (chemical signature) as Earth’s oceans. Hartley 2 is the first Kuiper Belt comet to be investigated for its composition. Other comets subjected to similar analyses had yielded unfavorable results (the composition of the water was not exactly that of Earth’s oceans). Subsequent analyses of the deuterium abundance in the water of other comets, and especially of numerous asteroids, led to the conclusion that the water in Earth’s oceans is largely of asteroidal, not cometary, origin.
