An international team of astronomers, led by Keele University researcher John Southworth, has managed to detect an atmosphere around GJ 1132b, a ‘super-Earth’ exoplanet in the constellation Vela, 39.3 light-years from us.
Artist’s impression of the super-Earth GJ 1132b. Image credit: MPIA.
GJ 1132b (Gliese 1132b) orbits the red dwarf star GJ 1132, which is only 1/5 the size of our Sun and is cooler and much fainter than the Sun, emitting just 1/200th as much light.
“GJ 1132’s proximity to the Sun means that it is comparatively bright and therefore well-suited to analyses aimed at constraining the properties of both the star and the planet,” Dr. Southworth and co-authors said.
The detection of an atmosphere around GJ 1132b marks the first time an atmosphere has been detected around an extrasolar planet with a mass and diameter close to that of Earth.
“Whilst we’re still a long way from detecting life on exoplanets, this discovery is the first step,” noted Dr. Southworth, lead author of a paper reporting the discovery in the March 31, 2017 issue of the Astronomical Journal (arXiv.org preprint).
“With this research, we have taken the first tentative step into studying the atmospheres of smaller, Earth-like, planets.”
The astronomers used the 2.2-m ESO/MPG telescope at La Silla Observatory in Chile to observe the planet simultaneously at seven different wavelength bands spanning the optical and near-infrared.
As GJ 1132b is a transiting planet, it passes directly between Earth and its host star every 1.6 days, blocking a small fraction of the star’s light.
From the amount of light lost, scientists can deduce the planet’s size — in this case only 1.43 times that of Earth.
Crucially, the new observations showed the planet to be larger in one of the seven wavelength bands. This suggests the presence of an atmosphere that is opaque to this specific light — making the planet appear larger, but transparent to all the others.
Different possible versions of the atmosphere were then simulated by Dr. Southworth and his colleagues.
According to those models, an atmosphere rich in water and methane would explain the observations very well.
“We simulated a range of possible atmospheres for this planet, finding that those rich in water and/or methane would explain the observations of GJ 1132b,” Dr. Southworth said.
“The planet is significantly hotter and a bit larger than Earth, so one possibility is that it is a ‘water world’ with an atmosphere of hot steam.”
The presence of an atmosphere on GJ 1132b is a reason for cautious optimism.
Very low-mass stars are extremely common, and are known to host lots of small planets. But they also show a lot of magnetic activity, causing high levels of X-rays and UV light to be produced which might completely evaporate the planets’ atmospheres.
However, the properties of GJ 1132b show that an atmosphere can endure this for billion of years without being destroyed.
Given the great number of very low-mass stars and planets, such atmospheres could mean that the preconditions for life are quite common in the Universe.
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John Southworth et al. 2017. Detection of the atmosphere of the 1.6 Earth mass exoplanet GJ 1132b. AJ 153, 191; doi: 10.3847/1538-3881/aa6477
