What can an exoplanet leaking helium teach astronomers about the formation and evolution of exoplanet atmospheres? This is what a recent study published in *Nature Astronomy* hopes to address as an international team of scientists investigated atmospheric escape on a puffy exoplanet. This study has the potential to help scientists better understand the formation and evolution of gas giant planets, specifically with many gas giant planets observed orbiting extremely close to their stars.
For the study, the researchers used the Near Infrared Imager and Slitless Spectrograph (NIRISS) onboard NASA’s powerful James Webb Space Telescope (JWST) to observe WASP-107 b, which is located approximately 211 light-years from Earth, has an orbital period of only 5.7 days, and is classified as a “super-puff” exoplanet, also called "cotton candy" exoplanets. This classification is because while the radius of WASP-107 b is slightly smaller than Jupiter, its mass is less than one-tenth, or just under 30 Earth masses. This means WASP-107 b’s density is incredibly small (~0.13 g/cm3) compared to the four giant planets of our solar system: Jupiter (1.33 g/cm3), Saturn (0.69 g/cm3), Uranus (1.27 g/cm3), and Neptune (1.64 g/cm3), along with its atmosphere being very bloated compared to the giant planets in our solar system.
After observing several transits of WASP-107 b, which is when the planet passes in front of its star, the researchers found that not only was WASP-107 b losing chunks of its helium atmosphere, but it seemed to be constant. For example, the researchers found evidence of helium atmospheric escape before the planet transits its star (pre-transit), during its transit, and even after its transit (post-transit). Essentially, WASP-107 b is exhibiting a giant atmospheric tail of helium the researchers estimate extends tens of the planet’s radii, while also identifying water, ammonia, carbon dioxide, methane, and carbon monoxide within the escaping atmosphere. All these features could help astronomers better understand planetary atmosphere formation and evolution, especially on rocky planets.
“On Earth, atmospheric escape is too weak to drastically influence our planet,” said Dr. Vincent Bourrier, who is an assistant professor specializing in exoplanets at the University of Geneva and a co-author on the study. “But it would be responsible for the absence of water on our close neighbor, Venus. It is therefore essential to fully understand the mechanisms at work in this phenomenon, which could erode the atmosphere of certain rocky exoplanets.”
While the number of confirmed exoplanets recently exceeded 6,000, super-puff planets remain some of the most intriguing and mysterious types of exoplanets ever discovered. This is because they don’t resemble anything we see in our solar system while also challenging scientists’ understanding of exoplanet formation and evolution, specifically due to the lack of density discussed above. Aside from WASP-107 b, other examples of super-puff exoplanets include HAT-P-67 b, WASP-94 A b, Kepler-79 d & e, HIP 41378 f, and Kepler-51 b, c, & d. Along with its super-puff classification, WASP-107 b also joins a growing population of exoplanets with atmospheric escape, and specifically helium escape. Examples of these exoplanets include WASP-69 b, HAT-P-11 b, GJ 3470 b, HD 209458 b, HD 189733 b, WASP-12 b, and Kepler-63 b.
The researchers note the importance of using JWST for studying planetary evolution, as JWST continues to demonstrate its incredible ability to study exoplanets and their atmospheres. Along with identifying atmospheric escape and chemical composition, JWST has also contributed to exoplanet science through identifying atmospheric temperature and wind changes, characterizing Earth-sized exoplanets, and identifying key biosignatures like water, methane, and carbon dioxide, as conducted in this study.
What new insight into atmospheric escape and exoplanet leaking helium will researchers make in the coming years and decades? Only time will tell, and this is why we science!
As always, keep doing science & keep looking up!
Further Reading:
Nature Astronomy - Continuous helium absorption from both the leading and trailing tails of WASP-107 b
NASA – WASP-107 b
EurekAlert! - Helium leak on the exoplanet WASP-107b
Universe Today - "Super-Puff" Exoplanets Aren't Like Anything We've Got in the Solar System