Just recently, an exo-planetary system called TRAPPIST-1, with seven known planets close in size to Earth, was announced by astronomers. Some of those planets are in the star's habitable zone, meaning that they could potentially be habitable for some kind of life. Then, another Earth-sized world was found orbiting the star GJ 1132b, and may have water and methane in its atmosphere. Now, another similar planet has been found orbiting another nearby star. It is also close in size to Earth and resides in the star's habitable zone. According to scientists, it is another prime candidate in the search for alien life and may even be the best one yet.
The planet, called LHS 1140b, is of a type known as a "super-Earth" which is larger than Earth but smaller than ice giants like Uranus and Neptune. It is about 1.4 times the size of Earth, but has a mass about seven times greater than our planet. That means it is most likely rocky with a dense iron core. It is estimated, based on knowledge about the star, to be approximately five billion years old.
LHS 1140b orbits a red dwarf star 40 light-years away, in the constellation of Cetus (The Sea Monster), so it only receives about half as much sunlight from its star as Earth does from the Sun, but it also orbits ten times closer to its star. It therefore lies within the habitable zone, meaning that it could potentially have liquid water on its surface, depending on other conditions.
As noted by lead author of the new study, Jason Dittmann of the Harvard-Smithsonian Center for Astrophysics, “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.”
Since the planet transits in front of its star as seen from Earth, astronomers should be able to study its atmosphere further with additional studies, including with the Hubble Space Telescope.
According to Xavier Delfosse and Xavier Bonfils at the CNRS and IPAG in Grenoble, France, “The LHS 1140 system might prove to be an even more important target for the future characterisation of planets in the habitable zone than Proxima b or TRAPPIST-1. This has been a remarkable year for exoplanet discoveries!”
Artist's conception of LHS 1140b
Astronomers made the discovery using the MEarth facility, which detected the first dips in light as the exoplanet transited in front of the star. ESO’s HARPS instrument, the High Accuracy Radial velocity Planet Searcher, then made follow-up observations which confirmed the existence of LHS 1140b. HARPS also helped pin down the orbital period and allowed the exoplanet’s mass and density to be measured.
Red dwarf stars are known for usually being very active, and frequent solar flares could pose a problem for any nearby planets. LHS 1140, however, appears to be fairly stable, which is good for a planet's potential habitability.
"The present conditions of the red dwarf are particularly favourable - LHS 1140 spins more slowly and emits less high-energy radiation than other similar low-mass stars," said team member Nicola Astudillo-Defru from Geneva Observatory in Switzerland.
The super-Earth planet known to be orbiting the nearest star, Proxima Centauri (Proxima b), is of course closer, but analysis of its atmosphere, if any, is difficult since it doesn't transit in front of its star. Proxima Centauri is also a red dwarf, the most common type of star in our galaxy. Not much is known yet about the seven planets in the TRAPPIST-1 system, but studies suggest at least some of them could be rich in water. As previously reported, another recently discovered super-Earth, GJ 1132b, also orbits a red dwarf star and may have an atmosphere rich in water and methane, according to initial observations.
The holy grail of exoplanet studies is to find another world similar to Earth. We don't yet know what the actual conditions on LHS 1140b are, but, but even so, its discovery is yet another step closer to finding "Earth 2.0."