Distant planet may have lost and replaced its atmosphere
Image credit: NASA, ESA, AND R. HURT
A planet orbiting a distant star may have lost its atmosphere and subsequently gained a second one through volcanic activity, scientists operating Nasa’s Hubble Space Telescope have said.
The planet, dubbed GJ 1132 b (artist interpretation pictured), is thought to have begun as a gaseous world with a thick atmosphere filled with hydrogen.
But it is believed to have quickly lost its primordial hydrogen and helium atmosphere due to the intense radiation of the hot, young star it orbits.
To the surprise of astronomers, Hubble observed an atmosphere which, according to their theory, is a “secondary atmosphere” that is present now. Based on a combination of direct observational evidence and inference through computer modelling, the team reports that the atmosphere consists of molecular hydrogen, hydrogen cyanide, methane and also contains an aerosol haze.
Modelling suggests the aerosol haze is based on photochemically produced hydrocarbons, similar to smog on Earth.
The researchers believe the current atmospheric hydrogen was from the original atmosphere which was absorbed into the planet’s molten magma mantle and is now being slowly released through volcanic processes to form a new atmosphere.
The atmosphere we see today is believed to be continually replenished to balance the hydrogen escaping into space.
“It’s super exciting because we believe the atmosphere that we see now was regenerated, so it could be a secondary atmosphere,” said study co-author Raissa Estrela of Nasa’s Jet Propulsion Laboratory (JPL).
“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.’”
The findings could have implications for other exoplanets, planets beyond our solar system.
“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,” said lead author Mark Swain of JPL.
“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.”
In some ways, GJ 1132 b is quite comparable to Earth with a similar density, size, and age, both being about 4.5 billion years old.
But the planets are thought to have profoundly different formation histories, with Earth orbiting at a comfortable distance from our Sun while GJ 1132 b is so close to its red dwarf star that it completes an orbit around it once every day and a half.
Given GJ 1132 b’s hot interior, the team believes the planet’s cooler, overlying crust is extremely thin, perhaps only hundreds of feet thick or much too feeble to support anything resembling volcanic mountains. Its flat terrain may also be cracked like an eggshell due to tidal flexing. Hydrogen and other gases could be released through such cracks.
Nasa’s upcoming James Webb Space Telescope has the ability to observe this exoplanet. Webb’s infrared vision may allow scientists to see down to the planet’s surface.
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