An artist’s impression of the planet (smaller one)

New Delhi, July 11: A surge of excitement hit Italian physicist Giovanna Tinetti as the unmistakable signatures of water originating from a world outside the solar system began to seep into her computer.

Using a telescope in space to peer at a distant star, an international research team led by Tinetti has discovered water for the first time on a planet so far away that its light takes 64 years to reach Earth.

While the planet is too close to its star and thus too hot to support life, the scientists say the discovery suggests that water — and life-friendly environments — may be more common on extrasolar planets than previously believed.

“We’re exploring the atmospheres of planets outside the solar system,” said Tinetti, who is now at the University College, London. “And this is the first glimpse of a special molecule in the atmosphere of an extrasolar planet,” Tinetti told The Telegraph.

The discovery, to be announced in the journal Nature tomorrow, is based on the observations of subtle changes in the light from the star as the planet passed in front of it. The studies, conducted with the help of Nasa’s Spitzer telescope orbiting Earth, show that the planet appears to absorb starlight in a manner that can only be explained if there was water vapour in its atmosphere.

The planet — HD 189733b — orbits a star similar to the Sun, but is 30 times closer to its star than the Earth is to the Sun. Scientists estimate that temperatures on the planet could be anything from 1200 degrees to 2000 degrees.

Unlike the small, rocky Earth, HD 189733b is a gas giant made up mostly of hydrogen. Most of the 220-odd extrasolar planets hitherto discovered are gas giants similar to Jupiter or Saturn.

Astronomers had earlier used theories of planet formation to predict that water should be one of the most abundant molecules after hydrogen in gas giants. “It always feels great when observations match predictions,” Tinetti said.

Scientists believe the discovery is also significant because it demonstrates the potential of a special technique to indirectly detect water on planets that are so far away that they cannot be observed directly.

“With new telescopes in the future, we should be able to use the same technique on smaller, rocky planets,” Heather Knutson, an astronomer at Harvard University, who was not part of the team, told The Telegraph.

In April this year, astronomers had announced their discovery of the first extrasolar planet that appears to fall within the habitable zone of a star — the region around a star where water will occur in its liquid form.

“In the back our of our brains, we associate water with life. But this planet is far too hot and hostile and for life,” Tinetti said.

“The ‘holy-grail’ for today’s planet hunters is to find an Earth-like planet that also has water in its atmosphere. But finding water on an extrasolar gas giant is a vital milestone along that road of discovery.”