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Atmosphere Detected Around an Earth(ish)-Sized Planet

Just 39 light years away, GJ 1132b is 1.4 times the Earth’s radius and has an atmosphere that may be composed of steam or methane

The view from GJ 1132b (Dana Berry)
smithsonian.com

The seven recently discovered Earth-sized planets orbiting the star TRAPPIST-1 have received a lot of attention lately. But there's a new cool kid on the block: GJ 1132b. Hanging out in the constellation Vela and orbiting a dwarf star GJ 1132, this planet is getting a lot of attention—it's the first with a radius and mass most similar to Earth that hosts an atmosphere, Sarah Lewin reports for Space.com.

The researchers noticed its atmosphere while taking images of the planet’s host star with the 2.2 meter ESO/MPG telescope in Chile. As the planet transited across the face of the star, they measured its light at different wavelengths. In one particular wavelength the planet appeared larger and its brightness dimmed, a sign that an atmosphere was absorbing some of the light from the star.

“While this is not the detection of life on another planet, it’s an important step in the right direction: The detection of an atmosphere around the super-Earth GJ 1132b marks the first time that an atmosphere has been detected around an Earth-like planet other than Earth itself,” says John Southworth, a researcher at Keele University in the United Kingdom and first author of a paper on the find in The Astronomical Journal.

"Earth-like" however, is used liberally here. The planet itself has surface temperatures of at least 700 degrees Fahrenheit, Sarah Kaplan reports for The Washington Post. "GJ 1132b is so close to its sun that it more likely resembles Venus than Earth," she writes.

It’s also not the first time an atmosphere has been detected around an exoplanet. As Gizmodo's George Dvorsky explains, researchers have detected atmospheres previously around two other exoplanets, Jupiter-like gas giants including 55 Cancri e, which is eight times as large as our planet, has a surface temperature of 3630 Fahrenheit and a year that lasts just 18 hours. However, planet GJ 1132b (Smithsonian.com is formally requesting a cooler name, like Atmos), is much more similar to Earth.​ Dvorsky reports it's 1.6 times Earth’s mass and has 1.4 times the radius.

The find, however, was not a complete surprise. Ever since astronomers announced the discovery of GJ 1132b in November 2015, they speculated that it might be possible to detect whether the planet had an atmosphere because it is so close, only 39 light years away.

“If this planet still has an atmosphere, then we might find other, cooler planets that also have atmospheres and orbit small stars,” astronomer and exoplanet hunter Zachory Berta-Thompson told Ian Sample at The Guardian at the time. “We can then imagine interrogating the atmospheres for molecules that come from life.”

There's no signs of life on GJ 1132b. In the press release, Southworth says that the team looked at many different types of atmospheres that could possibly exist on the planet. “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,” he says. “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.”

Tom Louden, a physicist at the University of Warwick who is not involved in the study, tells Dvorsky that he thinks the atmosphere is likely less life-friendly. “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,” he says. “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.”

As Lewin reports, the finding is particularly exciting because M-class dwarf stars are the most common stars in the galaxy. In fact, 20 of our 30 nearest neighbors are M dwarfs. If planets orbiting these volatile stars can maintain an atmosphere, it opens up the possibility of many, many more habitable planets in the universe.

According to the press release, other telescopes including the Hubble, ESO’s Very Large Telescope, and the James Webb Space Telescope, which launches next year, will focus on GJ 1132b.

Editor's Note April 7, 2017: We've used a bit of humor in the headline to reinforce a serious point. Though the planet is the smallest-known exoplanet with an atmosphere, at 1.4 times the radius of Earth, it is considered a super-Earth.

About Jason Daley

Jason Daley is a Madison, Wisconsin-based writer specializing in natural history, science, travel, and the environment. His work has appeared in Discover, Popular Science, Outside, Men’s Journal, and other magazines.

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