Evrim Yazgin
Cosmos science journalist
Astronomers have used NASA’s James Webb Space Telescope (JWST) to identify bizarre characteristics of an exoplanet.
It is the size of Jupiter, but hot and with 10 times less mass (still 30 times more mass than Earth). It is also the first time a planet has been discovered to have east-west asymmetry in its atmosphere from space-based observations.
WASP-107 b’s weird atmosphere is described in a new paper published in Nature Astronomy.
The gas planet orbits its host star which is about 211 light-years from Earth. It was discovered in 2017. WASP-107 b orbits its star every 5.7 days at a distance less than 1/18th the distance between Earth and the Sun.
Its proximity to its host star means that WASP-107 b is tidally locked, showing the same face to the star as it orbits – like the Moon around the Earth. One side of the planet is in perpetual daytime, the other always in darkness.
WASP-107 b is also unique because of its extremely low density and gravity. This makes its atmosphere more inflated than other planets of similar mass.
“We don’t have anything like it in our own solar system,” says lead author Matthew Murphy, a graduate student at the University of Arizona, US. It is unique, even among the exoplanet population.”
Murphy’s team was able to analyse the features of the exoplanet’s atmosphere as it transited – passed in front of – its host star. As the star’s light shone through WASP-107 b’s atmosphere, its chemical make up and properties could be determined.
The researchers used the unprecedented precision of the JWST to separate signals from the atmosphere’s eastern and western sides.
“These snapshots tell us a lot about the gases in the exoplanet’s atmosphere, the clouds, structure of the atmosphere, the chemistry and how everything changes when receiving different amounts of sunlight,” Murphy explains.
WASP-107 b is also of interest because its temperature is intermediate between the temperature of planets in our solar system and the hottest exoplanets.
It is a balmy 470°C – more than the melting point of zinc.
“Traditionally, our observing techniques don’t work as well for these intermediate planets, so there have been a lot of exciting open questions that we can finally start to answer,” Murphy says. “For example, some of our models told us that a planet like WASP-107 b shouldn’t have this asymmetry at all – so we’re already learning something new.”
“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,” adds co-author Thomas Beatty, from the University of Wisconsin-Madison in the US.
