Potentially habitable 'super-Earth' is prime target for atmospheric study

The newly discovered exoplanet is believed to have a density of around seven times that of Earth, and a diameter of 18,000 km (11,184 miles), making it 1.4 times the size of our blue marble.

This artist's impression shows the exoplanet LHS 1140b, which orbits a red dwarf star 40 light-years from Earth and may be the new holder of the title "best place to look for signs of life beyond the Solar System". And like our star, they emit flares, releasing massive amounts of radiation into space which, in turn, can damage the atmospheres of nearby planets (Earth is protected by its magnetic field). But just like Earth, this planet sits in the coveted habitable zone, the region around a star where temperatures are just right for liquid water to pool on a planet's surface. When the star was young, it would have bathed the planet in a harsh ultraviolet glare that could have stripped any water from the atmosphere, leading to a runaway greenhouse effect like we see on Venus. However, Dittmann and colleagues believe that LHS 1140b is large enough to have sustained a magma ocean on its surface for millions of years. This ocean may have infused the atmosphere with steam for a prolonged period, which would have effectively replenished the planet's water supply.

The researchers propose that LHS 1140b probably formed in a manner similar to Earth.

Most of these planets, also known as Super Earths, were thought to be made from gas but Mr Tan said the new planet was definitely rocky.

The exoplanet's star, LHS 1140, bears little resemblance to our Sun; it is less than one-fifth of our star's mass and much cooler and dimmer, according to a study announcing the planet's discovery today in the journal Nature.

Red dwarfs are much smaller and cooler than the Sun and, although LHS 1140b is ten times closer to its star than the Earth is to the Sun, it only receives about half as much sunlight from its star as the Earth. Even though Proxima Centauri is a relatively chilly star, explaining Proxima b's habitable-zone status, such a tight orbit presents dangers to the exoplanet.

The planet was discovered by observing the tiny reduction in the light from the star when the planet passed in front of it. Mr Tan said the minute dip in light was like "observing a candle burning in Albany from Perth". And a good chunk of them also lie in the habitable zone. But finding a super-Earth with a rocky composition is pretty rare, and the fact that it's in the habitable zone makes the discovery even sweeter.

Since the star it orbits is quite small and relatively close to us, it may be possible for current telescopes and those now under construction to determine if the planet has an atmosphere.

But if it's too far, any water will freeze, as is seen on Mars. TRAPPIST-1 remains the record-holder for the most Goldilocks planets discovered orbiting a star. It's here, researchers say, where we might find the best chance in our search for life.

What makes LHS 1140b notable is that it is not bombarded with as much high-energy radiation that batters other planets around similar stars.

The discovery was initially made with an array of eight autonomous telescopes at Harvard University's MEarth facility at Cerro Tololo observatory near La Serena, Chile.

At 40 light years away, LHS 1140b is one of the closer potentially habitable exoplanets we have found.

MEarth is a planet hunting facility, created to monitor the nearby low-mass M dwarfs for transiting planets. When Earth-sized exoplanets pass in front of those stars, scientists are able to identify them.

The orbit is seen nearly edge-on from Earth and as the exoplanet passes in front of the star on each of its orbits it blocks a little of its light every 25 days.

  • Carolyn Briggs