Studying far-away exoplanets is tricky business, but by probing their atmospheres (still tricky business), scientists can gain valuable insights into their composition, including the probability of life. This arm of astronomy took a promising step forward today, with researchers detecting what they say is the first evidence of an atmosphere around an Earth-sized planet.
Ever since it was discovered in 2015, scientists have suspected that the exoplanet GJ 1132b could play host to an atmosphere. 39 light years away, this Venus-like world circles its red dwarf parent star in an very tight orbit, at a distance of around 1.4 million miles (2.25 million km). To put that into perspective, the closest Mercury ever ventures to our own sun is 29 million mi (46 million km).
When exoplanets orbit closely like this, the blinding light from their parent star makes it impossible to see them directly. While instruments under development, like the Project Blue telescope, are hoped to snap our first photographs of these far away worlds, for now scientists rely on a technique called transiting.
This occurs when the exoplanet passes in front of its parent star, creating a dip in light that can be picked up here on Earth. This can not only reveal the presence of an exoplanet, as it has done thousands of times now for scientists working with NASA's Kepler space telescope, but can also reveal characteristics about the far away world.
Using this method to track the fraction of starlight blocked by GJ 1132b, scientists were able to gauge its size – around 1.4 times the size of Earth, with 1.6 times the mass. But in new observations using the ESO/MPG telescope in Chile, an international team of scientists observed GJ 1132b in seven different wavelength bands, finding that one of the infrared wavelengths revealed a planet that seemed to be larger in size.
They believe that this indicates the presence of an atmosphere, whose composition presents as opaque at that specific wavelength and therefore makes the planet seem larger than it is. This technique has previously indicated the presence of atmospheres around exoplanets closer in size to Jupiter, but the team says its findings are the first to reveal an atmosphere of an Earth-sized planet. The team simulated various potential versions of the atmosphere on GJ 1132b, and say that modeling suggests an atmosphere rich in methane and water would explain the observations well.
This raises the prospect of a "water world" with an atmosphere of hot steam, making life improbable. With its close proximity to its parent star, the steamy atmosphere likely drives a strong greenhouse effect – scientists have previously estimated that these characteristics could see temperatures as high as 450° F (232° C).
But the discovery is a promising sign in the search for life as a whole. Because M Dwarfs, the type of star at the center of this system, are highly active and the most common type of star, it bodes well for similar findings elsewhere in the universe. This is because these stars unleash radiation and flares that tend to strip neighboring planets of their atmospheres. That GJ 1132b has endured this barrage for billions of years – so long that we can detect it – means that these atmospheric conditions might actually be quite common.
The team hopes the secrets of GJ 1132b will be further unravelled following additional study with the Hubble Space Telescope, ESO's Very Large Telescope and the James Webb Telescope when it launches next year.
The research was published in the Astronomical Journal.