Earth-like oceans may be common on planets in other solar systems, greatly increasing the chances of extra-terrestrial life, evidence suggests.

The oceans on Earth were filled long ago by water-bearing comets and asteroids, scientists believe.

Now new observations of a distant star at the end of its life have indicated that such water carriers are common in our galaxy, the Milky Way.

Astronomer Dr Roberto Raddi, from the University of Warwick, said: “Our research has found that, rather than being unique, water-rich asteroids similar to those found in our solar system appear to be frequent. Accordingly, many of planets may have contained a volume of water, comparable to that contained in the Earth.

“It is believed that the Earth was initially dry, but our research strongly supports the view that the oceans we have today were created as a result of impacts by water-rich comets or asteroids”.

The scientists used the William Herschel Telescope in the Canary Islands to detect a large amount of hydrogen and oxygen – the constituents of water – in the atmosphere of a “white dwarf”, the compact remnant of a sun-like star.

This was direct evidence of water being delivered to the star by a large body. The object would have been similar in size to Ceres, the largest asteroid in our solar system, measuring 900 kilometres (559 miles) across.

“The amount of water found … is equivalent to 30 – 35% of the oceans on Earth,” said Dr Raddi.

Water is regarded as an essential pre-requisite for Earth-like life.

Many planets have been identified that occupy “habitable” orbital paths around their parent stars where temperatures are mild enough for liquid surface water to exist. But how many of them actually possess water is unknown.

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