An Unforgiving Environment

Put on your friendliest face and say hello to the newest member of our planetary neighborhood: Barnard’s star b.An international team led by researchers from the Carnegie Institution for Science announced today that they’ve detected an exoplanet orbiting Barnard’s star, the closest single star to Earth at just six light-years away. The astronomers calculate that the newfound world, dubbed Barnard’s star b, is about 3.2 times the mass of Earth and orbits its host star once every 233 days. The so-called super-Earth is the second-closest known exoplanet, trailing just behind Proxima Centauri b at a mere 4.2 light-years away, and that could make it an exciting place to look for life.But unlike Proxima b , which shows promising signs of habitability, Barnard’s star b is likely inhospitable to life as we know it.Barnard’s star is a cool, low-mass red dwarf estimated to be at least twice as old as our Sun, with some calculations putting it at 12 billion years old. Consequentially, the dim, ancient star only emits about 0.4 percent of the energy that the Sun does, providing little warmth to its surrounding environment.Using ESO’s High Accuracy Radial velocity Planet Searcher (HARPS) and Ultraviolet and Visual Echelle Spectrograph (EVES), the research team found that Barnard’s star b orbits about 60 percent closer to its host star than Earth does to the Sun. But despite its snug proximity, the planet still sits beyond the chilly star’s “snow line” — the region where water and other volatiles start turning into ice. At this distance, the planet only receives about two percent of the energy that the Sun gives to Earth, putting its surface temperature at a frigid -340 degrees Fahrenheit (-170 degrees Celsius).“The temperature of the star relative to the orbit of the detected planet means that it likely does not have surface liquid water, which is a prime characteristic for deeming a planet even potentially habitable,” said Johanna Teske, a NASA Hubble Postdoctoral Fellow at Carnegie and co-author of the study’s paper, published today in the journal Nature . “A planet in the ‘habitable’ or surface liquid water zone of Barnard’s star would have a period between 10 and 40 days, much shorter than the detected planet at 233 days.”On top of the planet’s icy nature, the actions of its host star could also be a threat to life. It isn’t uncommon to see flares blasting out of red dwarfs during their younger and middle-aged years, but witnessing one shoot out of an older one is quite rare. Back in 1998, though, astronomers saw a powerful flare erupt from Barnard's star, causing its temperature to soar from about 3,100 kelvins to at least 8,000. Such flares likely contain hefty amounts of X-ray radiation, and it’s not clear whether Barnard’s star b has an atmosphere to protect it from them.