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Ice and rock planet, a lot like Earth

New Delhi Jan. 25: An international team of astronomers has discovered what could be an ice and rock planet outside the solar system and called it the most Earth-like among all extrasolar worlds found so far.

The planet orbits a red star about 20,000 light years away from the sun, close to the centre of the Milky Way galaxy. It appears to be five times heavier than the Earth and its distance from its parent star is estimated to be three times the Earth’s orbit.

Theoretical studies suggest that at this distance, the surface temperature of the planet would be minus 220 degrees Celsius. Astronomers speculate that it is a frigid world whose rocks are buried beneath frozen oceans.

The discovery, to be announced in the journal Nature tomorrow, was based on a relatively new technique to find small planets. It has bolstered hopes of finding planets in the habitable zone around distant stars.

“We’ve been looking for a second Earth, and this is the most Earth-like planet we know of so far outside our solar system,” Daniel Kubas, a German astronomer at the European Southern Observatory in Chile, South America, said.

“This is exactly the type of planet predicted by current theories to be among the most common in the universe,” David Bennett, a team member at the University of Notre Dame in the US, told The Telegraph. Astronomers from 12 countries participated in the near-continuous round-the-clock observations of the skies and data analysis leading to the discovery of the planet.

While astronomers have found more than 150 planets outside the solar system over 15 years, almost all of them resemble Jupiter or Saturn, the gas giants in the solar system. Nearly all were detected through the wobble of a star caused by its planet’s gravity. This technique can find only large Jupiter-sized planets or small planets that orbit too close to their stars ' and thus are too hot ' to support life.

The new planet was detected with the help of a technique based on observing the effect of gravity on starlight. The gravity of a planet around a distant star adds to the magnification of incoming starlight. “We don’t see the planet or even the star that it is orbiting. We just see the effect of gravity,” said Andrew Williams, a team member from Perth.

“This is actually the first and only planet discovered so far that is in agreement with theories for how our own solar system formed,” said Uffe Grae Jorgensen, a scientist with the Neils Bohr Institute in Copenhagen, Denmark.

Current theories assume that planets are formed through the accumulation of small rocks to form cores of planetesimals that build up as cores of planets. These rocky cores then accrete gas ' if available ' to gradually burgeon into gas giants.

Astronomers believe there are far more rocky frozen worlds than Jupiter-like gas giants.

“When there’s not enough gas, they end up as low-mass planets,” Kuback said.

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