The delivery of water to Earth by way of comets or asteroids is likely not a unique phenomenon and is probably occurring in numerous other distant planetary systems, a new study strongly indicates.

New evidence that numerous cosmic bodies, including comets and asteroids, contain significant quantities of water, supports the theory that they can deliver it to Earth-like planets and create environments in which life could form, the study, led by the University of Warwick in England, suggests.

Water-rich asteroids similar to those found in our solar system are common in the galaxy, the researchers report in the Monthly Notices of the Royal Astronomical Society.

"Our research has found that, rather than being unique, water-rich asteroids similar to those found in our solar system appear to be frequent," says Roberto Raddi of Warwick's Astronomy and Astrophysics Group.

Many scientists believe the Earth started out dry, with the oceans our planet possesses today the result of impacts of water-bearing asteroids or comets, he notes.

"Accordingly, many planets may have contained a volume of water comparable to that contained in the Earth," he says.

The Warwick astronomers used the William Herschel Telescope located in the Canary Islands to detect amounts of oxygen and hydrogen in the atmosphere of a distant white dwarf star in quantities that suggest a water-carrying asteroid was disrupted by the star's gravitational attraction and delivered its water into the star's atmosphere, where it was separated into hydrogen and oxygen.

"The amount of water found ... is equivalent to 30 to 35 percent of the oceans on Earth," Raddi says, suggesting an asteroid similar in size to the dwarf planet Ceres, the largest asteroid in our solar system at almost 600 miles across.

When the water delivered into a star separates into its oxygen and hydrogen components, the oxygen — a relatively heavy element — sinks deep into the star over time, while the lighter hydrogen will continue to float near the surface, explains study co-author Boris Gänsicke.

"There are many white dwarfs that hold large amounts of hydrogen in their atmospheres, and this new study suggests that this is evidence that water-rich asteroids or comets are common around other stars than the sun," he says.

If such stars have planets, they also could receive water from such asteroids and comets, Raddi suggests.

The Warwick study "confirms that asteroids can deliver their constituents (rocks and ice) onto the surface of planets in the inner parts of the planetary systems orbiting other stars, likely within what is known as the habitable zone," he says.