Webb solves the mystery of puffy atmosphere in exoplanet WASP-107 b 

An artist's illustration of the gas giant exoplanet WASP-107 b
An artist’s illustration of the gas giant exoplanet WASP-107 b. (Image credit: NASA, ESA, CSA, R. Crawford (STScI))

Astronomers have solved the long-standing mystery of puffy atmosphere in exoplanet WASP-107 b.

An exoplanet is a planet that orbits another star outside our solar system. Exoplanet WASP-107 b orbits the star WASP-107, located about 210 light-years away from Earth in the constellation Virgo.

WASP-107 b is a “hot Neptune” type exoplanet, meaning the size of the exoplanet is similar to Neptune but its temperature is higher than Neptune due to its close proximity to the host star.

WASP-107 b orbits its host star at a distance of about 5 million miles (one-seventh of the distance between Mercury and the Sun) and takes only 5.72 days to complete its one orbit. 

The exoplanet is tidally locked due to its close proximity to the host star. So the same side of the planet always faces the sun, and the other side is in complete darkness. It is very similar to our moon, which is tidally locked to our Earth. That’s why we always see the same side of the moon.

However, the most surprising fact about the exoplanet WASP-107 b is that the planet is about 80% of the size of Jupiter in terms of volume but has a mass less than 10% of Jupiter’s, making it one of the least dense exoplanets known.

Astronomers had no answer as to how a small core holds such a puffy atmosphere, as it contradicts the theory of planet formation and evolution.

Finally, astronomers have been able to solve this mystery by using the spectroscopic data from the James Webb Space Telescope, combined with earlier observations from the Hubble Space Telescope.

The spectrum of the exoplanet WASP-107 b was captured using the Hubble and James Webb space telescopes
The spectrum of the exoplanet WASP-107 b was captured using the Hubble and James Webb space telescopes. It shows the amounts of different wavelengths (colors) of starlight blocked by the atmosphere of the gas giant exoplanet WASP-107 b. (Image credit: NASA, ESA, CSA, R. Crawford (STScI))

The spectrum clearly indicates the presence of water (H2O), carbon dioxide (CO2), carbon monoxide (CO), methane (CH4), sulfur dioxide (SO2), and ammonia (NH3) in the atmosphere of WASP-107 b, allowing astronomers to estimate its temperature and the mass of its core.

The very low spike of methane (CH4) in the spectrum indicates a surprising lack of methane in the atmosphere of WASP-107 b. As a result, the tidal heating is able to puff up the atmosphere of the hot gas giant WASP-107 b.

And astronomers have calculated that the mass of its core is at least twice as massive as originally estimated, which makes more sense in terms of how planets form. 

Two new scientific papers have been published on the above findings in Nature on May 20, 2024. These are:

A warm Neptune’s methane reveals core mass and vigorous atmospheric mixing

A high internal heat flux and large core in a warm neptune exoplanet  

Related article: Webb detects first merger of two black holes after the big bang 

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Ashim Chandra Sarkar founded Space & Telescope in 2022. He holds a M.Sc. in physics and has five years of research experience in optical astronomy. His passion for astronomy inspired him to open this website. He is responsible for the editorial vision of spaceandtelescope.com.

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