Excited astronomers have discovered the closest Earthlike rocky planet beyond our own Solar System – but it is almost certainly too hot for life. The new world, labelled GJ 1132b, lies right on our doorstep in cosmic terms, orbiting a star that is only 39 light-years away from us, or 370 trillion km (230 trillion miles). 

GJ 1132b is only 16 per cent bigger than Earth, with a diameter of about 14,800 km (9,200 miles), and scientists say their initial studies suggest it could have an atmosphere. But the bad news is the temperature appears to be higher than in a kitchen oven, making the new planet more like our twin neighbour Venus, which has a hell-like surface beneath a blanket of perpetual cloud.

The star it orbits is a red dwarf, so much cooler than our sun and 200 times less bright. But the planet lies so close, at a distance of only 1.4 million miles, compared to the 98 million miles between the Earth and the sun, that conditions are a scorching 230 C. If it ever had any water, it would have boiled away.

It was first spotted on May 10 by a robotic telescope called MEarth-South (corr) at the Cerro-Tololo Inter-American Observatory in Chile. The instrument systematically watches many thousands of similar stars, within 100 light-years of Earth, to spot any planets passing in from of them during their orbits. Such events – called transits – blot out some of the star’s light, causing it to dim slightly. Planets around other stars are technically known as exoplanets.

Once the fade caused by GJ 1132b was detected, a more powerful Magellan Clay telescope in Chile was turned on it with a highly sensitive instrument that was able to gauge its size and weigh it up. From its size and mass, scientists determined its density which indicates that is is rocky like the Earth. If you were able to stand on it, you would weigh a fifth more than you do on Earth!

Since the planet is so close, astronomers will now seek to study its atmosphere in detail using NASA’s Hubble space telescope in orbit, and other giant telescopes being built for mountaintops or to be sent into space, including NASA’s forthcoming James Webb Space Telescope which will dwarf Hubble.

The eight separate telescopes that make up the MEarth South Observatory, which detected GJ 1132b. Image credit: CfA/Jonathan Irwin

Leader of the discovery team, Dr Zachory Berta-Thompson, of the Massachusetts Institute of Technology, said: “This planet is cool enough that it can retain an atmosphere. So we think this planet probably still has something of a substantial atmosphere, in its current state.

“If we find this pretty hot planet has managed to hang onto its atmosphere over the billions of years it’s been around, that bodes well for the long-term goal of studying cooler planets that could have life,

He added: “The temperature of the planet is about as hot as your oven will go. It’s too hot to be habitable – there’s no way there’s liquid water on the surface. But it is a lot cooler than the other rocky planets that we know of.”

“We finally have a target to point our telescopes at, and dig much deeper into the workings of a rocky exoplanet, and what makes it tick. This planet is going to be a favourite target of astronomers for years to come.”

“We think it’s the first opportunity we have to point our telescopes at a rocky exoplanet and get that kind of detail, to be able to measure the colour of its sunset, or the speed of its winds, and really learn how rocky planets work out there in the universe. Those will be exciting observations to make.”

Astronomer David Charbonneau, of the Harvard-Smithsonian Center for Astrophysics, at Cambridge, Massachusetts, said: “Our ultimate goal is to find a twin Earth, but along the way we’ve found a twin Venus. We suspect it will have a Venus-like atmosphere too, and if it does we can’t wait to get a whiff.”

In July, NASA announced the discovery of a planet similar to Earth orbiting the star Kepler-452. It lies much further away than the newest find, at a distance of 1,400 light-years.