THE search for planets like Earth has had a setback after low water-levels were found on planets that were expected to have plenty.

Three planets orbiting stars like the sun were seen as ideal candidates to find water-vapour, a key characteristic of Earth-like worlds.

But a team of astronomers using Nasa's Hubble Space Telescope to study the planets - which are 60 to 900 light-years away, and are as hot as 2200ÚC - have found they are virtually dry.

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Scientists from the Institute of Astronomy at the University of Cambridge said water levels were one-tenth to one-thousandth of what they had expected.

Astronomer Dr Nikku Madhusudhan said: "The levels we found were much lower than expected. These results show just how challenging it could be to detect water on Earth-like exo-planets in our search for potential life elsewhere."

More sensitive instruments may be needed to find the "holy grail" of a planet similar to Earth, he added.