Observations by NASA’s Hubble Space Telescope suggest that a distant planet called GJ 1132 b might have lost its original atmosphere and created a new one.
Discovered in 2015, GJ 1132 b is located approximately 41 light-years away from Earth and was believed to have started out as a gas planet with a thick atmosphere of hydrogen around 4.5 billion years ago. The diameter of this “sub-Neptune” was several times that of Earth, but when it lost its hydrogen and helium atmosphere because of the radiation from its host star, the planet was left with nothing but its core that is approximately the same size as our planet and is why it is called a “super Earth”. It is tidally locked with only one side facing its M-type star at all times and completes a full orbit around it every 1.6 Earth days.
But that wasn’t the end of the story as observations made by Hubble seemingly showed that the planet formed a “second atmosphere” that contains molecular hydrogen, hydrogen cyanide, methane, and aerosol haze (similar to smog on Earth). Scientists think that the hydrogen in its new atmosphere came from the original atmosphere that was absorbed into the molten magma mantle and the volcanic activity is now releasing it back.
Raissa Estrela, who is from NASA’s Jet Propulsion Laboratory (JPL) in Southern California and a co-author of the study, stated how incredible this discovery was, “It’s super-exciting because we believe the atmosphere that we see now was regenerated, so it could be a secondary atmosphere.” “We first thought that these highly irradiated planets could be pretty boring because we believed that they lost their atmospheres. But we looked at existing observations of this planet with Hubble and said, ‘Oh no, there is an atmosphere there.’”
Mark Swain from JPL and the lead author of the study explained this further, “How many terrestrial planets don’t begin as terrestrials? Some may start as sub-Neptunes, and they become terrestrials through a mechanism that photo-evaporates the primordial atmosphere. This process works early in a planet’s life, when the star is hotter.” “Then the star cools down and the planet’s just sitting there. So you’ve got this mechanism where you can cook off the atmosphere in the first 100 million years, and then things settle down. And if you can regenerate the atmosphere, maybe you can keep it.”
He went on to ask, “The question is, what is keeping the mantle hot enough to remain liquid and power volcanism?” There may be a significant amount of tidal heating which is caused by friction from when the planet’s rotation and orbit so the gravitational “pumping” would keep the mantle liquid for some time. Since it has a very thin surface crust, there wouldn’t be any tall volcanoes but rather a bunch of cracks where hydrogen and other gases could possibly seep out into the second atmosphere.
Scientists plan on learning more about the planet with the upcoming launch of the James Webb Space Telescope later this year. “If there are magma pools or volcanism going on, those areas will be hotter,” Swain noted, adding, “That will generate more emission, and so they’ll be looking potentially at the actual geologic activity – which is exciting!” Their research can be read in full here.
A picture and video of GJ 1132 b can be seen here.