A red dwarf star named Gliese 1132 or GJ 1132 for short (astronomers for short and their funny nicknames!) Smolder in about 41 light years from the sun in the southern constellation Vela, only a few degrees from the southern cross. In 2015, astronomers using the MEarth South telescope array at the Cerro Tololo Inter-American Observatory (CTIO) in Chile found an Earth-sized planet orbiting extremely close to the little red star. Known as GJ 1132b, orbits the planet in a blistering 1.6 days. It is believed that its original hydrogen and helium atmosphere was long blown away by the strong stellar winds that the planet experiences due to its extreme proximity to its parents. New observations from the Hubble Space Telescope revealed a surprise from the fast exoplanet; it seems to have reshaped an atmosphere!
GJ 1132b was relatively easy to spot because it is a transiting exoplanet. This means that, from our point of view, the planet runs exactly between us and its parent star. This event causes the light captured by the star to decrease periodically and predictably. This “transit method” of detecting exoplanets is one of the most effective methods of detecting planets around other stars.
Astronomers don’t just measure the star’s brightness, however. The spectrum of light is also carefully measured. In the case of GJ 1132b, the starlight passing through its atmosphere interacts with the various molecules inside. This leaves a characteristic type of spectral fingerprint in the light. Astronomers can only infer the composition of the atmosphere by observing the light that has passed through the “air” of GJ 1132b!
The table above shows the spectrum of the atmosphere of GJ 1132b. Signatures of methane, hydrogen cyanide, and aerosols are highlighted. Photo credit: NASA, ESA, and P. Jeffries
What kind of air did we find in this “secondary atmosphere”? The spectroscopic data show molecular hydrogen (H2), methane (CH4), hydrogen cyanide (HCN) and an aerosol haze that resembles smog. This smog is caused by numerous photochemical reactions motivated by the outrageous radiation that is always present in such narrow star quarters. Needless to say, the atmospheric pressure on the surface of GJ 1132b appears to be similar to that of Earth, however this is not a suitable environment for humans!
To be so close to a star, even one as faint as a red dwarf, is an extreme environment. It is believed that the atmosphere is constantly replenishing. What could be the source of the atmospheric renewal in this strange world? Due to the strong tidal forces close to a star, the interior of the planet is likely to be very hot and active. The crust is believed to be extremely thin, only a few hundred meters (the earth’s crust under your feet is many tens of kilometers thick). With such a thin solid surface, the magma below constantly releases dissolved gases into the atmosphere. While the gas source is volcanic, it’s interesting to note that the crust likely cannot withstand the weight of mountain volcanoes and is more like a cracked egg shell.
Not only is GJ 1132b right next to its parent star and surrounded by a poisonous atmosphere, but it is also different from Earth in other ways. The exoplanet has not always been a rocky world like ours. It is believed to be the solid remains of the core of a “sub-Neptune” gas planet. The original hydrogen and helium atmosphere would have been gigantic compared to the mopping nitrogen and oxygen envelope on earth.
The planet did not have the titanic gravity of something called Super Jupiter. The stellar winds struck the scorching hot world early in their life; The dense atmosphere would have eroded into space and become part of the solar wind that tore them from their homeworld.
This exciting discovery of a secondary atmosphere around the rocky core of a vaporized sub-Neptune exoplanet around a nearby star makes GJ 1132b a particularly tempting target for the upcoming James Webb telescope. The JWST should be able to capture a much clearer picture of the exoplanet’s atmosphere and various properties.
The brilliant, gold, hexagonal mirrors of the James Webb Space Telescope are slated to hit the market later this year. Credit NASA
The discovery and study of exoplanets are some of the most compelling reasons why it is reasonable to say that we are in the middle of a true astronomical golden age. Exoplanets grew up in the 1990s and were just one area of speculation. Today we are confident that there are thousands of exoplanets. We infer the presence of hundreds of billions of other worlds just within the Milky Way. We can even see the composition of the atmosphere of earth-sized planets like GJ 1132b! You can’t help but be excited to see what discoveries for exoplanet explorers like the brilliant team behind this latest remarkable finding are just around the corner.
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