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The first Earth-like planet ever seen outside of the solar system has been discovered

The “super-Earth” is about seven times the mass of our own planet and appears to be composed of about 50 per cent water, an essential condition for organic life to survive.

Its discovery boosts the possibility that there are planets in neighbouring solar systems that meet all the criteria that scientists believe are needed to support living organisms.

The super-Earth, which is called GJ1214b, is in orbit around a red dwarf star that is about one-fifth the size of the Sun and is about 40 light years away.

Although it is too hot to sustain life, the discovery shows that even very basic ground-based technologies are capable of finding almost-Earth-sized planets in warm, life-friendly orbits.

“Despite its hot temperature, this appears to be a waterworld,” said Zachory Berta, a graduate student at the Harvard-Smithsonian Center for Astrophysics who first spotted the planet. “It is much smaller, cooler, and more Earthlike than any other known exoplanet.”

He added that some of the planet’s water should be in the form of exotic materials such as Ice VII (seven), a crystalline form of water that exists at pressures greater than 20,000 times Earth’s atmosphere.

The discovery, which is published today in the journal Nature, was made through a major search programme, called MEarth, aimed at discovering Earth-sized planets elsewhere in the galaxy. The project is monitoring 2,000 of the smallest stars in the sky for hints that they have orbiting planets.

Any star whose brightness dims for about an hour, and repeats that dimming at regular intervals over the course of days and weeks, probably has an orbiting planet crossing briefly in front of it, blocking a fraction of the star’s light. The planet's size can be determined through the amount of dimming.

The stars were scrutinised one by one used eight ground-based telescopes no larger than ones typically owned by amateurs.

“This means that anyone else with a similar telescope and a good camera can detect it too. Students around the world can now study this super-earth,” said David Charbonneau, head of the MEarth project.

The team found that a faint star around 40 light years away from Earth undergoes repeated dimming for 52 minutes every 1.6 days.

The only plausible interpretation was that a planet orbits the star with an orbital period of 1.6 days.

The next step for astronomers is to try directly to detect and characterise the atmosphere, which will require a space-based instrument like Nasa’s Hubble Space Telescope. The planet is only 40 light-years from Earth, easily within the reach of current observatories.

“Since this planet is so close to Earth, Hubble should be able to detect the atmosphere and determine what it’s made of,” said Dr Charbonneau. “That will make it the first super-Earth with a confirmed atmosphere — even though that atmosphere probably won’t be hospitable to life as we know it.”