Key Takeaways:
- GJ 1132 b is a super-Earth exoplanet that is about 1.6 times the mass of Earth. It orbits a red dwarf star in the constellation Vela, only 40 light years away from Earth.
- The planet was once thought to have lost its atmosphere due to intense radiation from its parent star. However, recent observations suggest that it may have reestablished an atmosphere, possibly of volcanic origin.
- This finding is significant because it is the first time a secondary atmosphere has been detected on an exoplanet. It could have implications for our understanding of planetary formation and the possibility of finding life on other planets.
- The atmosphere of GJ 1132 b is thought to be composed mainly of hydrogen and hydrogen cyanide, which suggests that it may have been outgassed from the planet’s interior.
- This discovery suggests that even super-Earths that are very close to their host stars may still have atmospheres that can be studied by astronomers.
GJ 1132 b was formerly a smallish gas giant planet. The massive gas envelope surrounding it was destroyed by intense radiation from its parent star, leaving behind only a desiccated rocky core that is roughly 1.6 times the mass of our planet. This is known as the super-Earth.
After examining Hubble Space Telescope observations of GJ 1132 b, a team led by scientists at NASA’s Jet Propulsion Laboratory (JPL) in Pasadena has discovered something extremely strange: the planet appears to have reestablished an atmosphere. Furthermore, the composition of the gases suggests a volcanic origin.
From what we know about our own solar system, rocky planets frequently undergo complete atmospheric makeovers. Twice in Earth’s history has the atmosphere been entirely recreated: once by volcanic eruptions and meteorite strikes, and again by the appearance of life. Mars is currently in its third or second atmosphere. However, this is the first record of a secondary atmosphere on an exoplanet.
Certain researchers believe that the detection is not as certain as the team says it is. If this is accurate, however, it may have greater implications for planetary formation theories and show that researching exoplanet atmospheres can provide insight into beneath processes.
In the constellation Vela, GJ 1132 b orbits a red dwarf that is only 40 light years away from Earth. It was found by a team led by Harvard University that was searching for transits, or when a planet passes in front of its host star and slightly dims it, using a variety of small ground-based telescopes.
Astronomers can also examine the wavelengths that an exoplanet’s atmosphere absorbs as light from its host star travels through it during transits to learn more about the planet’s atmosphere. A European team reported discovering a water-rich atmosphere using this technique. Some of the planet’s discoverers, however, questioned this after making additional observations, claiming their data supported the idea that the planet had no atmosphere at all. An absence of atmosphere was also consistent with theory, which states that a rocky planet too close to its parent star would rapidly lose its initial atmosphere and evaporate into space.
However, the latest research provides additional support to the theory that GJ 1132 b has an atmosphere. It was accepted for publication in the Astronomical Journal and released on the arXiv preprint server. Methane and hydrogen cyanide were among the gases that the researchers identified using data that Hubble gathered. “This world really stood out because it is small, and with a clear spectral signature,” says JPL’s Mark Swain, who led the work.
This does not, however, totally reject theory. With its temperature reaching an intense 440 degrees Fahrenheit (227 degrees Celsius), the team used a model to simulate the planet’s evolution and came to the conclusion that GJ 1132 b probably did lose its initial atmosphere of hydrogen and helium during the first 100 million years of its existence. This indicates that the second atmosphere of the planet is what they detected.
Raissa Estrela of JPL, a co-author of the study, believes that “it is very likely that the planet lost everything at the very beginning.” “But the transit observations show spectral features which means there definitely is an atmosphere.” She goes on to say that these characteristics imply that the gases have a high hydrogen content and a low oxygen content, which raises the possibility that volcanic outgassing is the cause of them.
Origins of volcanoes
For research on exoplanets, finding a secondary atmosphere produced by volcanic activity would be a first.
All known exoplanet atmospheres before GJ 1132 b are believed to have formed in the same way: protoplanets grow by accreting material from the disk of gas surrounding their host stars, and their atmospheres are derived from a leftover envelope of gas during the initial formation of the local system.
Swain and colleagues turned to a paper that suggests a stage in the process where a nascent planet accreting a hydrogen atmosphere can absorb that hydrogen into its molten mantle, since their modelling ruled out the possibility of this primordial atmosphere surviving on GJ 1132 b. The team suggests that volcanic activity could later release this hydrogen reservoir.
The team claims that there is evidence for this cycle to have occurred on the ancient Earth, when the composition of the air was very different from what it is today. “There are some rocks that have been dug up from the Earth’s mantle that show a very low oxygen content,” says Swain. Many geologists believe that these rocks originated during the time that Earth had a deep-seated, primordial atmosphere that was rich in hydrogen.
The group depicted this possibility for GJ 1132 b and discovered that what they saw in the atmosphere could be produced if this hydrogen-rich magma released its gas above ground. This includes features like the planet’s unusually high levels of hydrogen cyanide, which makes up about 0.5 percent of the planet’s total atmosphere.
The study is the first to connect atmospheric observations to formation theories of a planet’s mantle, which also has wider implications for studying exoplanet formation. One line of thought holds that many super-Earths are actually the leftover cores of sub-Neptunes — a class of gaseous planet whose growth stalls out before it can reach Neptune size — that have lost their primordial envelope of gas. This work suggests that even when those planets are extremely close to their host stars, these worlds might still have atmospheres that astronomers can investigate.
According to Swain, “our results provide observational evidence that this class of planet can reestablish an atmosphere, at least in some cases.”
