Water clouds surround nearby star

Distant comets may be vaporised by the hot star

By BBC News Online science editor Dr David Whitehouse

Astronomers should look for life in nearby planetary systems where comets swirl around blazing stars, releasing vast amounts of water.

Several billion years from now, the Sun will become a giant star and its power output will increase five thousand fold

David Neufeld, Johns Hopkins University

That is the assessment of American space agency (Nasa) scientists.

Using a satellite observatory, they have spied a star in the process of melting its cloud of comets, producing huge clouds of water vapour.

In our Solar System, just a few comets will fizzle away at the same time. But the new observations reveal a system in which billions of comets are being vaporised all at once.

"Although it is a pretty hot place there could be cooler worlds circling that star on which liquid water may exist, and if that is the case there may be life," said Dr Gary Melnick of Harvard University.

Water, water, everywhere

Evidence of water vapour swirling around a nearby star has been seen by the Submillimeter Wave Astronomy Satellite (Swas), a small radio observatory launched by Nasa in 1998.

Its sensors have focused on a giant star, designated IRC+10216. It is located 500 light-years (five thousand, million, million km, or three thousand, million, million miles) from Earth in the direction of the constellation Leo.

Swas in orbit

"What makes the results we are reporting so unusual is that we have found a cloud of water vapour around a star where we would not ordinarily have expected to find water," said Gary Melnick of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts.

It seems that the water vapour comes from icy comets that are melting due to the heat from the star, which is much hotter than our Sun.

"There must be about four Earth-masses of frozen water around IRC+10216 to produce the vapour cloud we see," said Melnick.

According to calculations, the comets circling IRC+10216 have a total mass broadly similar to the original mass of our Solar System's Kuiper Belt, a collection of comets and asteroids circling our Sun beyond the orbit of Neptune.

Earth's demise

In our planetary system, comets from the Kuiper Belt vaporise only occasionally, when they come too close to the Sun.

However, since IRC+10216 is much hotter than the Sun, the comets are being vaporised en masse.

David Neufeld, a professor of physics and astronomy at Johns Hopkins University in Maryland, believes what is happening to that nearby star could, in a few billion years, happen to our Sun - with apocalyptic consequences for the Earth.

"Several billion years from now, the Sun will become a giant star and its power output will increase five thousand fold," he said.

"As the luminosity of the Sun increases, a wave of water vaporisation will spread outwards through the Solar System, starting with Earth's oceans and extending well beyond the orbit of Neptune," he added.