New rocky super-Earth is fit for alien life, say astronomers

Astronomers have identified a new rocky planet in a habitable environment – and they say it is the best candidate for alien life yet found.

LHS 1140b
An artist’s of 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”. Image credit: ESO/

The world, dubbed a super-Earth, lies only 40 light-years away in the constellation of Cetus, the sea monster. It is orbiting a red dwarf star, just like TRAPPIST-1 which was revealed to have seven rocky planets in February.

This star has the less-catchy label of LHS 1140, and despite being relatively nearby, it is too faint to be seen without a large telescope. Its rocky super-Earth, which is a little larger and much more massive than Earth, and is thought to have an atmosphere, is labelled LHS 1140b.

It lies ten times closer to the star than Earth does to the Sun. However, because the star is smaller and cooler than the Sun, the planet is orbiting within its so-called habitable zone where water could exist in liquid form.

LHS 1140b’s orbit appears edge-on from Earth, so it regularly passes in front of its home star. An international team of astronomers discovered the new planet using a robotic telescope which noticed the star dim slightly when the planet blotted out part of its light.

new rocky planet LHS 1140b
How new rocky planet LHS 1140b might look close up as it begins to transit in front of the red dwarf star. Image credit: M. Weiss/CfA

It was confirmed in follow-up observations by a giant telescope operated by the European Southern Observatory (ESO) at La Silla in Chile, fitted with a sensitive instrument named HARPS, which is short for High Accuracy Radial velocity Planet Searcher. HARPS has been a prolific discoverer of planets around other stars.

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HARPS was able to measure the length of the planet’s orbital period, or year, and allow its mass and density to be calculated. Its mass is about seven times as much as Earth’s and its diameter is estimated to be 1,4 times greater at around 18,000 km (11,000 miles). Together, these statistics suggest the planet is rocky with a dense iron core.

Powerful telescopes in the future, including ESO’s Extremely Large Telescope and NASA’s forthcoming new observatory the James Webb Space Telescope (JWST) to study what it is made of by analysing the starlight shining through it.

The leader of the discovery team, Jason Dittmann of the Harvard-Smithsonian Center for Astrophysics (Cambridge, USA), said in a statement: “This is the most exciting exoplanet I’ve seen in the past decade. We could hardly hope for a better target to perform one of the biggest quests in science — searching for evidence of life beyond Earth.”

LHS 1140b is the only planet so far detected orbiting its red dwarf sun, but that may be simply because the others are too small to observe. By contrast, seven exoplanets have been detected orbiting the red dwarf TRAPPIST-1. Planets have also been pictured in their orbits around another star.

The new discovery is reported in the scientific journal Nature.

By Paul Sutherland

Paul Sutherland has been a professional journalist for nearly 40 years. He writes regularly for science magazines including BBC Sky at Night magazine, BBC Focus, Astronomy Now and Popular Astronomy, plus he has authored three books on astronomy and contributed to others.

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