British bookmakers wasted no time slashing the odds on aliens being discovered after astronomers announced Wednesday that they had discovered an Earth-like planet.

William Hill cut the odds on proving the existence of extra-terrestrial life from 1,000-1 to 100-1.

"We felt we had to react to the news that an Earth-like planet which could support intelligent life had been discovered -- after all, we don't know for sure that intelligent extra-terrestrial life has not already been discovered, but is being hushed up," said spokesman Graham Sharpe.

Astronomers reported they they had found a "super-Earth" more than 20 light years away, the most intriguing world found so far in the search for extra-terrestrial life.

For William Hill to pay out on an aliens bet, the prime minister has to confirm officially the existence of intelligent extra-terrestrial life within a year of the bet being placed.

"We have come a cropper before when, in the early 1960s, we offered 1000/1 about man walking on the moon before 1970," said Sharpe.

About five times the mass of Earth, the planet orbits a cool, dim "red dwarf" star in the constellation of Libra, the team from the European Southern Observatory said in a press release.

"Because of its temperature and relative proximity, this planet will most probably be a very important target of the future space missions dedicated to the search for extra terrestrial life," said Xavier Delfosse, a team member from France's Grenoble University.