Using the NASA/ESA Hubble Space Telescope, astronomers have found evidence of volcanic activity reforming the atmosphere of Gliese 1132b, a rocky exoplanet that is similar to Earth in terms of size and density.
An artist’s impression of Gliese 1132b. Image credit: NASA / ESA / R. Hurt, IPAC & Caltech.
Gliese 1132 is a red dwarf star located 39.3 light-years away in the constellation of Vela.
Otherwise known as GJ 1132, the star is only 1/5 the size, much cooler and fainter than the Sun, emitting just 1/200th as much light.
It hosts at least one planet — Gliese 1132b — that was recently discovered using the MEarth-South Observatory.
The alien world is about 1.2 times the size of Earth, and its mass is 1.6 times the mass of the Earth.
It circles its host star every 1.6 days at a distance of 1.4 million miles. As a result, the planet is baked to a temperature of about 232 degrees Celsius (450 degrees Fahrenheit).
Gliese 1132b appears to have begun life as a sub-Neptune planet with a thick blanket of atmosphere.
Starting out at several times the radius of Earth, the planet quickly lost its primordial hydrogen and helium atmosphere, which was stripped away by the intense radiation from its hot, young star. In a short period of time, it was reduced to a bare core about the size of Earth.
The new Hubble observations uncovered a secondary atmosphere that has replaced the first atmosphere of Gliese 1132b. It is rich in hydrogen, hydrogen cyanide, methane and ammonia, and also has a hydrocarbon haze.
The astronomers theorize that hydrogen from the original atmosphere was absorbed into the planet’s molten magma mantle and is now being slowly released by volcanism to form a new atmosphere.
This second atmosphere, which continues to leak away into space, is continually being replenished from the reservoir of hydrogen in the mantle’s magma.
“This second atmosphere comes from the surface and interior of the planet, and so it is a window onto the geology of another world,” said Dr. Paul Rimmer, an astronomer at the University of Cambridge.
“We first thought that these highly radiated planets would be pretty boring because we believed that they lost their atmospheres,” said Dr. Raissa Estrela, an astronomer at NASA’s Jet Propulsion Laboratory.
“But we looked at existing observations of this planet with Hubble and realized that there is an atmosphere there.”
Gliese 1132b is likely tidally locked, meaning that it has a permanent day and night side, presenting the same face to its star, much like the Moon is locked to the Earth.
“The question is, what is keeping the mantle hot enough to remain liquid and power volcanism? This system is special because it has the opportunity for quite a lot of tidal heating,” said Dr. Mark Swain, an astronomer at NASA’s Jet Propulsion Laboratory.
The researchers believe the crust of Gliese 1132b is extremely thin, perhaps only hundreds of meters thick. That’s much too feeble to support anything resembling volcanic mountains.
Its flat terrain may also be cracked like an eggshell by tidal flexing. Hydrogen and other gases could be released through such cracks.
“This atmosphere, if it’s thin — meaning if it has a surface pressure similar to Earth — probably means you can see right down to the ground at infrared wavelengths,” Dr. Swain said.
“That means that if astronomers use the James Webb Space Telescope to observe this planet, there’s a possibility that they will see not the spectrum of the atmosphere, but rather the spectrum of the surface.”
“And if there are magma pools or volcanism going on, those areas will be hotter. That will generate more emission, and so they’ll potentially be looking at the actual geological activity — which is exciting!”
A paper on the findings will be published in the Astronomical Journal.
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Mark R. Swain et al. 2021. Detection of an Atmosphere on a Rocky Exoplanet. AJ, in press; arXiv: 2103.05657
