This Is The Smallest Exoplanet Known To Have An Atmosphere

This Is The Smallest Exoplanet Known To Have An Atmosphere

Using a ground-based telescope, an international team of astronomers has detected traces of an atmosphere around an exoplanet located 39 light-years away. This exoplanet is not much larger than our own, making it the most Earth-like planet known to harbour an atmosphere.

Artist’s conception of GJ 1132b circling its red dwarf star. (Image: Dana Berry)

Detecting atmospheres around distant exoplanets isn’t anything special, particularly when the exoplanet in question is as big as Saturn or Jupiter. But as for smaller, Earth-sized planets, that’s a different story.

Prior to this latest discovery, astronomers had confirmed the presence of atmospheres on only two super Earth-sized planets, including the super-Earth 55 Cancri e. The term “super-Earth” is apt; this planet weighs as much as eight Earths, and its surface temperature blazes at 2050C. Let’s face it, 55 Cancri e is not very Earth-like at all.

That’s what makes the discovery of an atmosphere around exoplanet GJ 1132b so intriguing. As described in the Astronomical Journal, this planet is just slightly bigger than our own, weighing in at 1.6 Earth masses, and featuring a radius just 1.4 times larger than Earth’s. It’s the lowest mass super-Earth to have its own atmosphere — a discovery that represents an important step forward in the quest to find alien life.

Astronomers have known about GJ 1132b for a while, but a team led by the Max-Planck Institute for Astronomy wanted to get a better sense of its chemical composition. Using the GROND imager at the 2.2m ESO/MPG telescope in Chile, the astronomers scanned the planet in different wavelengths as it orbited its red dwarf every 1.6 days.

“We looked at how strongly the amount of light coming from the star decreased when the planet moved in front of its star,” explained study co-author Paul Mollière in an interview with Gizmodo. “We did that by letting the light pass through filters of multiple colours, and then found that the planet seems to block more stellar light in one of these filters. Hence, when viewed in light of that specific colour, the planet is bigger.”

This “bigger” perspective suggests the presence of an atmosphere around GJ 1132b — one consisting of possibly water and methane steam. This atmosphere is opaque when viewed at a specific frequency of infrared light (making the planet appear larger), but it’s invisible at other frequencies. That’s not the kind of thing you see in a planet without an atmosphere.

Tom Louden, a physicist at the University of Warwick who wasn’t involved in the study, was impressed that the astronomers were able to make these observations using a relatively small ground based telescope. “The majority of other studies that detect atmosphere features in exoplanets are either from state of the art space based telescopes or from much larger telescopes on the ground,” he told Gizmodo.

Louden also liked the way the astronomers measured multiple transits events (instances of the planet passing in front of its host star) in each of the spectral bands, making it less likely that the signal was due to an error or some kind of visual artefact. He says it’s completely plausible that water vapour is the likely cause of the signal, but argues there isn’t enough strong evidence to say with certainty that water is responsible.

This is now the smallest extrasolar planet known to host an atmosphere. But interestingly, Louden says this makes it much less likely to be “Earth-like” than other exoplanets in which atmospheres haven’t been detected.

“This detection implies it has a massive and extended atmosphere, composed largely of hydrogen and helium, probably more similar to Uranus or Neptune than to Earth,” said Louden. “To be clear, an atmosphere that we would think of as Earth-like would be completely invisible to these observations, and to all other currently existing telescopes.”

Well, that’s a bummer. He’s basically saying that we still don’t have the technological know-how to detect an Earth-like atmosphere around an Earth-like planet, and that the atmospheres we can detect are deep, thick monstrosities incapable of harbouring life (or at least, life as we know it). Hopefully, with the launch of the James Webb Space Telescope next year (fingers crossed), this will change, and we’ll finally find the Earth 2.0 we’re looking for.

[Astronomical Journal]