Astronomers capture image of uniquely inflated and asymmetric exoplanet

The findings were published in the journal Nature Astronomy.

“This is the first time that an east-west asymmetry of any exoplanet has been observed from space as it passes in front of its star,” said lead study author Matthew Murphy, a graduate student at the U of A Steward Observatory. A transit is when a planet passes in front of its star — much like the Moon does during a solar eclipse.

“I think observations from space have a lot of advantages over ground observations,” Murphy said.

The east-west asymmetry of an exoplanet refers to differences in atmospheric properties, such as temperature or cloud characteristics, observed between the planet’s eastern and western hemispheres. Determining whether this asymmetry exists is crucial to understanding the climate, atmospheric dynamics, and weather patterns of exoplanets — planets that exist beyond our solar system.

The exoplanet WASP-107b is tidally locked to its star. This means that the exoplanet always has the same face toward the star it orbits. One hemisphere of a tidally locked exoplanet always faces the star it orbits, while the other hemisphere always faces away, resulting in the exoplanet having a permanent day side and a permanent night side.

Murphy and his team used the James Webb Space Telescope to perform transmission spectroscopy, a technique astronomers use to gain insight into what makes up the atmospheres of other planets, Murphy said. The telescope took a series of snapshots as the planet passed in front of its host star, encoding information about the planet’s atmosphere. Using new techniques and the James Webb Space Telescope’s unprecedented sensitivity, the researchers were able to separate signals from the eastern and western sides of the atmosphere and get a more focused look at specific processes happening in the exoplanet’s atmosphere.

“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 it gets different amounts of sunlight,” Murphy said.

The exoplanet WASP-107b is unique in that it has a very low density and relatively low gravity, resulting in a puffier atmosphere than other exoplanets of its mass.

“There’s nothing like this in our own solar system. It’s unique even among the exoplanet population,” Murphy said.

WASP-107b has a temperature of about 300 degrees Celsius, which is between the temperature of the planets in our Solar System and the hottest known exoplanets.

“Traditionally, our observational techniques don’t work very well for these intermediate planets, so there are a lot of exciting open questions that we’re finally starting to answer,” Murphy said. “For example, some of our models tell us that a planet like WASP-107b shouldn’t have this asymmetry — so we’re already learning something new.”

Researchers have been studying exoplanets for nearly two decades, and numerous observations from both the ground and space have helped astronomers estimate what the atmospheres of exoplanets look like, said Thomas Beatty, an assistant professor of astronomy at the University of Wisconsin-Madison and co-author of the study.

“But this is the first time we’ve seen these kinds of asymmetries directly in the form of transmission spectroscopy from space. That’s the primary way we understand what exoplanetary atmospheres are made of. It’s really surprising,” Beatty said.

Murphy and his team are working on the observational data they’ve collected and plan to study what’s happening on the exoplanet in much more detail, including additional observations to understand what’s driving this asymmetry.

“For almost all exoplanets, we can’t even look at them directly, let alone know what’s going on on one side relative to the other,” Murphy said. “For the first time, we’re able to get a much more localized view of what’s going on in the atmosphere of an exoplanet.”