Okay, all life requires water, but how do you get the water in space last year on Independence Day, someone gazing toward the sky might have seen a sudden eruption of glowing dust. If you were looking through a large telescope, you might have thought you were looking at a fireworks display deep in outer space, when what you were in fact seeing was the plume of space dust released when a NASA space probe slammed into a comet 83 million miles away from Earth. The event captivated the public's imagination, but for the Deep Impact Team, the group of researchers behind the explosion, the hardest and most exciting work was just beginning.

Using photographs and data gathered by a spacecraft close to the dust-up, the team has now concluded there's water beneath the comet's surface. In a February article in the online edition of Science, lead author Jessica Sunshine '88, '94 PhD reported that a pool of water ice lies spread out over seven acres on the 4.6-billion-year-old comet.

"We have known for a long time that water ice exists in comets, but this is the first evidence of water ice on comets," says Sunshine, who is a chief scientist at Science Applications International Corporation, a research and engineering firm headquartered in San Diego.

Professor of Geological Sciences Peter Schultz, who is also part of the Deep Impact project, says the water is saturated with comet dust. "Basically, it's a dirty ice rink," he says. He points out that the ice lies over a relatively small portion of the comet's forty-five-square-mile surface, which means, he says, "we're not talking about a lot of water."

But the finding is still highly significant because it offers a possible explanation of how life began on Earth. Several billion years ago Earth was a barren, hot place, totally inhospitable to the creation of life. But if comets smashing into our planet brought water with them, they may have set off a chain reaction with other compounds on Earth that led to life. "Understanding a comet's water cycle and supply is critical to understanding these bodies as a system and as a possible source that delivered water to Earth," says Sunshine. "Add the large organic component in comets and you have two of the key ingredients for life."