Atmosphere detected around Earth-like planet
Could similar planets exist around other red dwarf stars?
The first detection of an atmosphere around an exoplanet with a mass and radius close to that of Earth’s has been made. The planet appears to be rich in water, raising hopes of one day finding a ‘second Earth’.
The planet, GJ 1132b, is 1.6 Earth masses and 1.4 Earth radii in size, and orbits a red dwarf star 39 lightyears away. Until now astronomers have concentrated on observing atmospheres around larger, Jupiter-like planets and superEarths. When these planets pass in front of their stars, their large atmospheres block out certain wavelengths of the starlight, allowing astronomers to examine the gases that surround them.
However, when observing red dwarfs, astronomers can examine the atmospheres of much smaller planets, as the changes in brightness are much clearer against the dimmer star. Scientists also have more precise models of red dwarfs than most stars, allowing them to calculate a star’s size more accurately and so work out the size of any planets orbiting them equally well.
It had previously been thought that strong stellar activity could blast away the atmospheres of planets around red dwarfs, however GJ 1132b’s atmosphere appears to have survived for billions of years. As these are the most common type of stars in the Galaxy, the find boosts hopes that many more Earth-like planets with atmospheres could be found.
Initial observations taken by the European Southern Observatory’s 2.2m ESO/MPG telescope showed that the planet is larger at infrared wavelengths, suggesting that there is water in the atmosphere to make it opaque to this light. But it is likely to be the next generation of telescopes, such as the Giant Magellan Telescope and the James Webb Space Telescope, which will confirm the presence of water in the planet’s atmosphere.
It is unlikely that the planet is habitable since it is only 3.7 million km from its star – around 10 times the Earth-Moon distance. The high levels of ultraviolet radiation at this distance would break the water apart into hydrogen and oxygen.
“On cooler planets, oxygen could be a sign of alien life and habitability. But on a hot planet like GJ 1132b, it’s a sign of the exact opposite – a planet that’s being baked and sterilised,” says Laura Schaefer from the Harvard Smithsonian Centre for Astrophysics, who took part in the study. www.eso.org