An international team of astronomers has discovered an extraordinary planet named WASP-193b. This planet is about 50% larger than Jupiter, yet it stands out as the second lightest planet ever identified.
Located roughly 1,200 light-years from Earth, WASP-193b is not just an astronomical oddity but also holds significant potential for advancing research on unusual planetary formations. The study detailing this discovery was published in the journal Nature Astronomy.
WASP-193b belongs to a category of planets humorously termed “puffy Jupiters.” These planets are characterized by their large size and extremely low density. The lightest known planet in this category is Kepler 51d, which is almost the size of Jupiter but a hundred times lighter.
For the past 15 years, the nature of puffy Jupiters has remained a mystery, according to lead study author Khalid Barkaoui. Due to its unique characteristics, WASP-193b presents an excellent opportunity for detailed study using the James Webb Space Telescope and other observatories.
“The planet is so light that it’s difficult to think of an analogous, solid-state material,” said Barkaoui, a postdoctoral researcher at the Massachusetts Institute of Technology. “The reason why it’s close to cotton candy is because both are mostly made of light gases rather than solids. The planet is basically super fluffy.”
### Low-Density Planet Presents a Big Challenge
WASP-193b is believed to be composed mainly of hydrogen and helium, posing a significant challenge for researchers due to its low density. Determining its mass was particularly difficult.
Typically, scientists use a method called radial velocity to measure a planet’s mass by observing the star’s spectrum shift as the planet orbits it. However, WASP-193b is so light that it did not create a detectable pull on its star.
Due to the minimal mass signal, it took the team four years to gather enough data to calculate WASP-193b’s mass accurately. Given the planet’s unusually low density, researchers conducted multiple data analysis trials to verify their findings.
“We were initially getting extremely low densities, which were very difficult to believe in the beginning,” said co-lead author Francisco Pozuelos, a senior researcher at Spain’s Institute of Astrophysics of Andalucia.
Eventually, the team determined that the planet’s mass is only about 14% of Jupiter’s mass, despite its larger size.
### Extended Atmosphere and Future Research
A larger size means a more extensive atmosphere, noted study coauthor Julien de Wit, an associate professor of planetary science at MIT. This makes WASP-193b an invaluable subject for studying atmospheric effects.
“The bigger a planet’s atmosphere, the more light can go through,” de Wit explained. “So it’s clear that this planet is one of the best targets we have for studying atmospheric effects. It will be a Rosetta Stone to try and resolve the mystery of puffy Jupiters.”
However, how WASP-193b formed remains unclear. Barkaoui mentioned that classical models of gas giant evolution do not adequately explain this phenomenon.
