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What’s big, with a fluffy, cotton candy-like composition? It turns out a planet.
An international coalition of astronomers recently discovered an unusual planet, dubbed WASP-193b, that is about 50% larger than Jupiter and somehow still the second lightest planet ever found.
But WASP-193b, located beyond our solar system, about 1,200 light-years from Earth, is not just a scientific rarity. The exoplanet could also hold the key to future research investigating atypical planetary formation, according to a study describing the discovery published Tuesday in the journal Planetary Science. Nature Astronomy.
This cotton candy planet is not alone; there are other similar planets belonging to a class that scientists jokingly call “bloated Jupiters”. The lightest planet ever discovered is Superpuffy Kepler 51dwhich is almost the size of Jupiter, but a hundred times lighter than the gas giant.
Bloated Jupiters have been a mystery for 15 years, said study lead author Khalid Barkaoui. But WASP-193b, because of its size, is an ideal candidate for further analysis by the James Webb Space Telescope and other observatories.
“The planet is so light that it is difficult to think of an analogous solid-state material,” said Barkaoui, a postdoctoral researcher in Earth, atmospheric and planetary sciences at the Massachusetts Institute of Technology in a press release. “The reason it is close to cotton candy is because they are both made primarily of light gases and not solids. The planet is basically super cute.”
Low-density planet presents great challenge
WASP-193b, which researchers believe is composed mainly of hydrogen and helium, was a huge puzzle for researchers to put together. Because the exoplanet’s density is so small for its size, calculating its mass has become a challenge.
Typically, scientists determine mass using a technique called radial velocity, in which researchers analyze how the speed of a star spectrum, a graph that indicates the intensity of light emissions in wavelengths, changes as a planet orbits it. The larger the planet, the more the star’s spectrum can shift – but this didn’t work for WASP-193b, which is so light that it exerted no pull on the star that the team could detect.
Because of how small the mass signal was, it took the team four years to collect data and calculate WASP-193b’s mass, Barkaoui explained. Because the extremely low numbers found were so rare, the researchers ran several data analysis tests, just to be sure.
“Initially we obtained extremely low densities, which were very difficult to believe at first,” said co-author Francisco Pozuelos, a senior researcher at the Spanish Institute of Astrophysics in Andalusia, in a press release.
Eventually, the team discovered that the planet’s mass is only 14% of Jupiter’s mass, despite being much larger.
But a larger size means a larger “extended atmosphere,” said study co-author Julien de Wit, an associate professor of planetary science at MIT. This means that WASP-193b provides an especially useful window into the formation of these bloated planets.
“The bigger a planet’s atmosphere is, the more light it can get through,” de Wit told CNN. “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 to solve the mystery of the bloated Jupiters.”
But it’s also unclear how WASP-193b formed, Barkaoui said. The “classical evolution models” of gas giants do not explain the phenomenon well.
“WASP-193b is an outlier of all the planets discovered so far,” he said.
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