A rocky exoplanet roughly the same size as Earth has been discovered orbiting a nearby low-mass star, thanks to new data gathered by ESO’s High Accuracy Radial velocity Planet Searcher (HARPS) at the La Silla Observatory in Chile. Located just 11 light-years from our Solar System, Ross 128b is the second closest known exo-Earth, after Proxima b, and the closest temperate exoplanet known around a quiet star.
This artist’s impression shows Ross 128b, with its red dwarf parent star in the background. Image credit: M. Kornmesser / ESO.
A research team led by Geneva Observatory astronomer Nicola Astudillo-Defru found that Ross 128b has a minimum mass of 1.35 Earth masses.
The planet orbits its host star, Ross 128 (also known as Proxima Virginis, Gliese 447 and HIP 57548), 20 times closer than the Earth is to the Sun, and takes just 9.9 days to circle it.
Despite this proximity, Ross 128b receives only 1.38 times more irradiation than the Earth.
As a result, the planet’s equilibrium temperature is estimated to lie between minus 60 and minus 4 degrees Celsius (minus 76 and plus 25 degrees Fahrenheit), thanks to the cool and faint nature of the parent star.
“Red dwarfs are some of the coolest, faintest — and most common — stars in the Universe,” Dr. Astudillo-Defru and colleagues said.
“This makes them very good targets in the search for exoplanets and so they are increasingly being studied.”
“Many red dwarf stars, including Proxima Centauri, are subject to flares that occasionally bathe their orbiting planets in deadly ultraviolet and X-ray radiation,” they noted.
“However, it seems that Ross 128 is a much quieter star, and so its planets may be the closest known comfortable abode for possible life.”
Although it is currently 11 light-years from Earth, Ross 128 is moving towards us and is expected to become our nearest stellar neighbor in just 79,000 years.
“Ross 128b will by then take the crown from Proxima b and become the closest exoplanet to Earth,” the astronomers said.
A paper reporting this discovery is published in the journal Astronomy & Astrophysics.
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X. Bonfils et al. A temperate exo-Earth around a quiet M dwarf at 3.4 parsecs. A&A, in press; doi: 10.1051/0004-6361/201731973
