The list of potentially habitable exoplanets has recently gained a promising new member. Researchers at the La Silla Observatory in Chile have found an Earth-like planet orbiting a nearby red dwarf star. At 11 light-years away, it is the second closest temperate exoplanet ever discovered, but other characteristics make it the most promising candidate to support life yet.
The exoplanet discussed in the study, published in the journal Astronomy and Astrophysics, is Ross 128 b. The planet, named after the red dwarf star it is orbiting, is very similar to Earth in size. Its calculated mass is 1.35 times that of the Earth. Remarkably, the planet orbits its star every 9.9 days, a result of it being 20 times closer to Ross 128 than our Earth is to the Sun.
Red dwarf stars are promising candidates to house exoplanets as they are the most abundant stars in our galaxy. For example, Proxima Centauri, our closest star, has recently made headlines for having a number of planets in the habitable zone or the range of distances from a star where a planet is capable of having liquid water.
These low-mass stars, however, are not the most hospitable. They are cool and faint which means planets are able to orbit fairly close to the star without burning up. That proximity has its consequences though. Red dwarfs, such as Proxima Centauri, experience frequent solar flares that unleash devastating ultraviolet radiation on nearby planets. The UV radiation is so intense it can eviscerate the atmosphere of these planets leaving them unsuitable for life.
Luckily, Ross 128 is a quiet red dwarf with limited solar flare activity. The researchers note that Ross 128 b receives just 1.38 times more irradiation than we receive here on Earth, meaning the exoplanet could still retain its atmosphere. The researchers go on to estimate that based on the irradiation, proximity to Ross 128, and the surface temperature of the red dwarf (which is half as hot as the Sun) Ross 128 b has an equilibrium temperature between -60°C and 20°C.
This discovery was made using the High Accuracy Radial velocity Planet Searcher (HARPS), a planet-hunting instrument developed by the European Southern Observatory. While HARPS is a powerful tool in the search for habitable planets, it is also limited.
In order to determine which exoplanets might actually be suitable for life, we have to be able to study the atmospheres of the planets. With the James Webb Telescope slated to launch in 2018 and the Extremely Large Telescope (ELT) scheduled to make its first observations in 2024 researchers will be able to analyze the atmospheres of distant planets like never before.
In the meantime, scientists are trying to locate the most promising exoplanets in order to know where to use these emerging instruments. Based on this recent study Ross 128 b could be the first planet we observe.