Habitable Zone

Astronomers have found three potentially habitable exoplanets less than fifty light years from Earth

An international team of astronomers has announced the discovery of three exoplanets in the habitable zones of their stars. That’s pretty exciting alone, but the closest is just 17 light years away.

They were found during analysis of archive data from two instruments — the Ultraviolet and Visual Echelle Spectrograph (UVES) and High Accuracy Radial velocity Planet Searcher (HARPS), both operated by the European Southern Observatory in Chile. Both instruments look for tiny wobbles in a star’s position caused by the orbit of planets around it.

The team found eight new worlds orbiting red dwarf stars (which make up at least three quarters of the stars in the Universe), three of which were in the habitable zone — the region where temperatures could allow for liquid water, making life more likely. The habitable candidates were Gliese 180c, thirty-eight light years away, Gliese 422b, forty-one light years away, and Gliese 682b, just seventeen light years away. The team also plans to follow up ten weaker signals.

They also found that the average red dwarf star has at least one near-Earth-sized planet, and one in four has one in the habitable zone. “According to our results, M dwarfs have very high rates of hosting systems of low-mass planets around them, and have a high probability of being hosts to super-Earths in their habitable zones,” wrote Mikko Tuomi, who led the study. “This makes them primary targets for searches of Earth-like planets, and possibly life.”

The three habitable planets, plus the slightly-too-hot Glieese 180b.

All the newly discovered planets orbit red dwarf stars between 15 and 80 light years from the Sun, making them relatively close to the Solar system. Two are even in the same star system. That’s good news for wannabe interstellar travellers, though don’t get too excited — the distance is still large enough that our technology today doesn’t allow for a return trip within a human lifetime. Plus we don’t yet know if they’re rocky or gaseous planets, or just dead worlds. Still, they’re a good start.

“We were looking at the data from UVES alone, and noticed some variability that could not be explained by random noise. By combining those observations with data from HARPS, we managed to spot this spectacular haul of planet candidates”, said Tuomi. “We are clearly probing a highly abundant population of low-mass planets, and can readily expect to find many more in the near future — even around the very closest stars to the Sun.”

The Planetary Habitability Laboratory at the University of Puerto Rico categorises Gliese 180b as in the habitable zone, despite the paper labelling it as too hot. The team there believes that stellar systems with multiple habitable planets are common. “So far, four out of the fifteen (~27%) known stellar systems with potentially habitable planets have more than one,” writes Abel Mendez Torres on the lab’s blog. The lab hosts the Habitable Exoplanets Catalog which keeps track of all the possible planets with the potential to support surface life as we know it.

The announcement of the discovery was made in the Monthly Notices of the Royal Astronomical Society.

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