The space rock was recovered by a group of boys in a small Texas town who saw it fall out of the sky in 1998.

Specimens taken to Nasa's Johnson Space Center in Houston were subjected to tests by Michael Zolensky and his colleagues. When they cracked open the rock they found tiny, purple spots of halite - crystals of sodium chloride, or table salt - along with minute amounts of briny water.

Others who have looked at the research, which is published in the journal Science, and have satisfied themselves that the rock was not contaminated when it fell to Earth, describe the discovery as "astonishing".

On Earth, halite generally forms when large areas of water evaporate. What this discovery suggests is that water was also flowing on the asteroid from which the meteorite came.

Either that, or the water was carried onto the asteroid by a comet or some other object carrying water.

Early Solar System

The rock is from what are called Chondrite meteorites, which are assumed to contain some of the most primitive materials from the early solar system.

The discovery of water inside the Texas rock should, therefore, shed new light on the conditions in the primordial solar nebula. This was the hot disk of dust and gas, with a protosun at the centre, from which the Earth and the other planets around us were believed to have formed, 4.5 billion years ago.

The meteorite was big news when it fell on the town of Monahans in west Texas on 22 March 1998.

The pieces were the subject of an ownership dispute with one specimen eventually auctioned for $23,000.

Further tests on the meteorite water will look for any trace elements. There will also be an examination of the different types (isotopes) of hydrogen and oxygen atoms that make up the water.