Earth's oceans may have come from comets

stunning close-up photo of Comet Hartley 2 from the Nov. 4, 2010 flyby performed by NASA's Deep Impact spacecraft. This close-up view of comet Hartley 2 was captured by the spacecraft's Medium-Resolution Instrument

File this one away as a new chapter in an old debate about the origin of Earth's water. Scientists say they have found water in a comet with nearly the same composition as water found in Earth's oceans.

Until now, astronomers' observations have failed to back up the idea that comets provided Earth's water. If the discovery holds up, it would buttress the argument that Earth's seas once might have been giant icebergs floating through space. Earlier studies maintained that early Earth lacked water.

The discovery was made during a study of the comet Hartley 2 by the Deep Impact/EPOXI spacecraft during its November 2010 pass by. has more about the findings here.