There is a significant difference between the two edges of the atmosphere of WASP-107b, a super-Neptune exoplanet about the size of Jupiter but only a tenth of its mass.
An artist’s illustration of the exoplanet WASP-107b. Image credit: Rachel Amaro, University of Arizona.
WASP-107 is a highly active K-type main sequence star located about 212 light-years away in the constellation of Virgo.
The star hosts WASP-107b, one of the least dense exoplanets known — a type that astrophysicists have dubbed ‘super-puff’ or ‘cotton-candy’ planets.
First discovered in 2017, the planet orbits very close to the star — over 16 times closer than the Earth is to the Sun — once every 5.7 days.
It has one of the coolest atmospheres of any of the exoplanets discovered, although at 500 degrees Celsius (932 degrees Fahrenheit) is still radically hotter that Earth.
The high temperature is thought to be a result of tidal heating caused by the planet’s slightly non-circular orbit, and can explain how WASP-107b can be so inflated without resorting to extreme theories of how it formed.
“This is the first time the east-west asymmetry of any exoplanet has ever been observed as it transits its star, from space,” said Matthew Murphy, a graduate student at the Steward Observatory.
“I think observations made from space have a lot of different advantages versus observations that are made from the ground.”
East-west asymmetry of an exoplanet refers to differences in atmospheric characteristics, such as temperature or cloud properties, observed between the eastern and western hemispheres of the planet.
Determining whether this asymmetry exists or not is crucial for understanding the climate, atmospheric dynamics and weather patterns of exoplanets.
Murphy and his colleagues used the transmission spectroscopy technique with the NASA/ESA/CSA James Webb Space Telescope.
“Researchers have been looking at exoplanets for almost two decades, and many observations from both the ground and space have helped astronomers guess what the atmosphere of exoplanets would look like,” said Dr. Thomas Beatty, an astronomer at the University of Wisconsin-Madison.
“But this is really the first time that we’ve seen these types of asymmetries directly in the form of transmission spectroscopy from space, which is the primary way in which we understand what exoplanet atmospheres are made of — it’s actually amazing.”
The astronomers have been working on the observational data they have gathered and are planning to take a much more detailed look at what’s going on with the exoplanet, including additional observations, to understand what drives this asymmetry.
“For almost all exoplanets, we can’t even look at them directly, let alone be able to know what’s going on one side versus the other,” Murphy said.
“For the first time, we’re able to take a much more localized view of what’s going on in an exoplanet’s atmosphere.”
The team’s paper was published today in the journal Nature Astronomy.
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M.M. Murphy et al. Evidence for morning-to-evening limb asymmetry on the cool low-density exoplanet WASP-107b. Nat Astron , published online September 24, 2024; doi: 10.1038/s41550-024-02367-9
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