What you need to know about cloud backup

NASA scientists have provided tantalising evidence that Earth's oceans may have originated in space, supplied by water-packed asteroids which deposited their loads in terminal collisions with our ancient planet.

Observations of 24 Themis - which at roughly 190 km (120 miles) wide is the largest of the Themis asteroid family lying between the orbits of Jupiter and Mars - have confirmed the presence of surface water ice and carbon-based organic materials.

However, data captured by the NASA Infrared Telescope Facility in Hawaii confirm the continued presence of surface water ice on 24 Themis, suggesting that as it sublimates into space, it's replenished by a sub-surface reservoir.

Don Yeomans, manager of NASA's Near-Earth Object Program Office, said: "For a long time the thinking was that you couldn't find a cup's worth of water in the entire asteroid belt. Today we know you not only could quench your thirst, but you just might be able to fill up every pool on Earth - and then some."

Asteroids, unlike the planets, have remained pretty well unchanged during the last four billion years. Accordingly, scientists speculate that any water and organic compounds the surviving bodies contain is likely to be similar to that which their now-destroyed cousins delivered to our primordial world.

It's possible, they say, that it was asteroids which delivered the building-blocks of life to Earth.

The 24 Themis findings offer further food for thought: since such celestial bodies contain considerable amounts of water, they could serve as "fueling stations and watering holes for future interplanetary exploration", as Yeomans put it.

It appears, then, that 24 Themis is an ideal target for Barack Obama's audacious plan to land on an asteroid, and thirsty astronauts could enjoy a refreshing cup of space water before heading off to Mars.

The NASA findings are published in the latest issue of Nature. ®

What you need to know about cloud backup