New planet discovered: Jupiter-sized but unexpectedly light

Scientists, with the help of the James Webb Space Telescope, have discovered a new planet, and it's very unusual. Although it is the size of our Jupiter, its mass is ten times lower. That’s not the end of the surprises.

Scientists from the University of Arizona described the unusual planet they discovered using the James Webb Space Telescope in the journal Nature Astronomy.

The distant globe is about the size of Jupiter but weighs only one-tenth of the gas giant's mass. The planet's atmosphere is also surprising: the left side significantly differs from the right.

"This is the first time the east-west asymmetry of any exoplanet has ever been observed as it transits its star, from space," says one of the scientists, Matthew Murphy. "I think observations made from space have a lot of different advantages versus observations that are made from the ground," he adds.

The asymmetry in question concerns differences in atmospheric parameters such as temperature or cloud cover, affecting the eastern and western hemispheres. This is crucial for understanding the climate, dynamic processes in the atmosphere, and weather phenomena.

"These snapshots tell us a lot about the gases in the exoplanet's atmosphere, the clouds, the structure of the atmosphere, the chemistry, and how everything changes when receiving different amounts of sunlight," says Prof. Murphy.

The planet, named WASP-107b, always faces the same side toward the star. "We don't have anything like it in our own solar system. It is unique, even among the exoplanet population," emphasizes the astronomer.

The average temperature is just under 930°F, placing it roughly in the middle between the temperatures of the hot planets of the Solar System and the hottest exoplanets.

"Traditionally, our observing techniques don't work as well for these intermediate planets, so there's been a lot of exciting open questions that we can finally start to answer. For example, some of our models told us that a planet like WASP-107b shouldn't have this asymmetry at all—so we're already learning something new," says Prof. Murphy.

"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," added Prof. Thomas Beatty, co-author of the discovery.

Scientists are already working on the observational data they collected to take a closer look at what is happening with the exoplanet, including understanding what causes the 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. For the first time, we're able to take a much more localized view of what's going on in an exoplanet's atmosphere," emphasizes Murphy.