Earth-like waterworld spotted

The planet is nearly three times as large as Earth and made almost entirely of water, forming a global ocean more than 15,000km deep.Astronomers detected the alien world as it passed in front of its sun, a red dwarf star 40 light years away in a constellation called Ophiuchus.

The discovery, made with a network of amateur telescopes, is being hailed as a major step forward in the search for planets beyond our solar system that are hospitable to life as we know it.

Measurements suggest the planet is shrouded in a thick atmosphere of hydrogen and helium that blocks visible light from its sun, plunging the watery surface into permanent darkness. The weight of the atmosphere keeps the water liquid despite it being a searing 120C to 282C.

Writing in the journal Nature, David Charbonneau at the Harvard-Smithsonian Centre for Astrophysics describes how his team used a suite of eight amateur-sized telescopes to spot the planet as it moved across the face of its star, which is less than 0.5 per cent as bright as our own sun.

The telescopes picked up a slight dimming in light from the star as the waterworld, named GJ1214b, passed in front of it every 1.6 days. The planet has a radius 2.7 times as large as the Earth’s and orbits at a distance of only two million kilometres from its star. Our own planet circles the sun at an average distance of around 150 mn kms.

“In time, we expect to find planets that are further away from their parent stars and so are likely to have surface temperatures much closer to those found on Earth,” he added.

The latest planet is only a stone’s throw away in astronomical terms, meaning scientists will be able to turn the Hubble Space Telescope towards it and analyse its atmosphere, potentially revealing signs of life.

“Using the Hubble, we can look at the atmosphere and say not only whether it’s habitable, but whether it’s inhabited,” Charbonneau said. “If we find oxygen in the atmosphere things will get really interesting, because on Earth all the oxygen in the atmosphere comes from life.”

The most likely composition of the planet is 75 per cent water, with 22 per cent silicon and 3 per cent iron forming a solid core, the scientists report.
In an accompanying article, Geoffrey Marcy, an astronomer at the University of California in Berkeley, said the extrasolar planet or ‘exoplanet’ provides “the most watertight evidence so far for a planet that is something like our own Earth outside our solar system”.

Zachory Berta, co-author, said: “Despite its hot temperature, this appears to be a waterworld. It is much smaller, cooler and more Earth-like than any other known exoplanet.”