Astronomers Observe Asymmetric Atmosphere on ‘Super-Puff’ Exoplanet WASP-107b

Astronomers using NASA's James Webb Space Telescope (JWST) have made groundbreaking observations of WASP-107b, an exoplanet that is uniquely inflated and exhibits an unusual atmospheric asymmetry.

This super-Neptune exoplanet, about the size of Jupiter but only one-tenth of its mass, shows distinct differences between the eastern and western sides of its atmosphere. The findings, published on September 24, 2024, in the journal Nature Astronomy, provide vital clues to the atmospheric dynamics and weather patterns of this distant world.

WASP-107b: A 'Super-Puff' Planet with Inflated Characteristics

First discovered in 2017, WASP-107b is one of the least dense exoplanets known, earning it the nickname "super-puff" or "cotton-candy" planet due to its extremely low density. It orbits the K-type main sequence star WASP-107, located about 212 light-years away in the Virgo constellation. Despite being similar in size to Jupiter, WASP-107b's mass is only a fraction of Jupiter’s, and its atmosphere is highly inflated due to its relatively low gravity.

The planet orbits much closer to its star than Earth does to the Sun, completing an orbit in just 5.7 days. This proximity causes WASP-107b’s atmosphere to reach temperatures of around 500 degrees Celsius (932 degrees Fahrenheit). The intense heat is likely due to tidal heating, caused by the planet’s slightly elliptical orbit, which keeps its atmosphere inflated. “WASP-107b’s inflated nature, despite its intermediate temperature, sets it apart from other exoplanets,” noted Matthew Murphy, the lead author of the study from the University of Arizona.

First Detection of East-west Atmospheric Asymmetry

For the first time, astronomers were able to detect an east-west asymmetry in the atmosphere of an exoplanet as it transited its star, using transmission spectroscopy from space. This technique, which allows scientists to study the light filtered through a planet's atmosphere during a transit, revealed significant differences in temperature and cloud properties between the planet's eastern and western hemispheres.

"This is the first time the east-west asymmetry of any exoplanet has ever been observed as it transits its star from space," said Murphy. The difference in atmospheric characteristics between the two sides of the planet is particularly intriguing because WASP-107b is tidally locked, meaning the same side always faces its star. Understanding this asymmetry is crucial for learning about the planet’s climate, weather patterns, and atmospheric dynamics.

The Role of JWST in Unlocking New Details

The James Webb Space Telescope, with its unprecedented precision, allowed astronomers to separate the signals from the eastern and western sides of the planet’s atmosphere, which had never been done before with such clarity. “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,” Murphy explained.

This breakthrough demonstrates the significant advantages of space-based observations. While ground-based telescopes have provided valuable data about exoplanets, space-based tools like JWST enable a more refined and detailed analysis of atmospheric conditions. “Observations from space have a lot of different advantages versus those made from the ground,” Murphy emphasized.

Unanswered Questions and Future Research

The discovery of the atmospheric asymmetry on WASP-107b challenges existing models of exoplanet atmospheres, which did not predict such a feature for this type of planet. “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,” Murphy said. This finding opens up new questions about the mechanisms driving this asymmetry and how common such features might be on other exoplanets.

Moving forward, Murphy and his team plan to conduct further observations to better understand what drives this asymmetry, including studying more exoplanets with similar inflated atmospheres. “For almost all exoplanets, we can’t even look at them directly, let alone know what’s going on one side versus the other,” Murphy added. By continuing to study these anomalies, researchers hope to refine their models of how atmospheric dynamics work on distant worlds.

The study not only advances our understanding of WASP-107b but also highlights the capabilities of JWST in exploring the complexities of exoplanet atmospheres. As additional data is gathered, astronomers may uncover even more surprising features of planets beyond our solar system, deepening our knowledge of planetary formation and behavior across the universe.