A planet larger than Jupiter, but with the density of cotton candy. As unreal as it may seem, it is WASP-193b, the second least dense planet discovered to date by an international team led by researchers from the Exotic laboratory at the University of Liège (Belgium), in collaboration with the Massachusetts Institute of Technology (MIT) and the Institute of Astrophysics in Andalusia (Spain), in a study published by Nature AstronomyMay 14, 2024. 50% larger than Jupiter, but seven times less massive, it represents a cosmic mystery for astronomers.
The new gas giant spotted by the WASP project
The new planet was first spotted by WASP (Wide Angle Search for Planets), a project dedicated to searching for giant planets around bright solar-like stars. This international collaboration uses two robotic observatories, one in the northern hemisphere (WASP-North) and the other in the south (WASP-South). Each observatory used an array of wide-angle cameras to measure the brightness of thousands of individual stars across the entire sky.
“Using data collected between 2006 and 2008, and again between 2011 and 2012, the WASP-South project detected periodic decreases in the brightness (dips of light) of WASP-193, a bright star located 1,200 years away. -light of the Earth These periodic variations are compatible with transits. (the temporary blocking of the light of a star by an orbiting planet, editor’s note) of a giant planet passing in front of the star every 6.25 days“, explains to Science and Future Khalid Barkaoui, postdoctoral researcher at the EXOTIC Laboratory at ULiège and first author of the study.
In-depth analysis from observatories in Chile
The researchers then used the TRAPPIST-Sud and SPECULOOS-Sud observatories, led by Michal Gillon, research director and astrophysicist at the University of Liège, located in the Atacama Desert in Chile, to measure transits in different lengths of wave and confirm that they were indeed caused by a planet. Subsequently, they carried out spectroscopic observations with the HARPS and CORALIE instruments, also located in Chile, to determine the mass of the planet.
This method allowed them to know the size of the planet, and observations of radial velocities made it possible to determine its mass. By combining these two methods, they were able to calculate the density of the planet.
“An extremely low density comparable to that of cotton candy”
To their surprise, the accumulated measurements revealed an extremely low density for the planet. “WASP-193b is 50% larger than Jupiter (1.5 Jupiter radii) but seven times less massive (0.14 Jupiter masses), which gives it an extremely low density (0.059 grams per cubic centimeter) comparable to that of cotton candy. In comparison, Jupiter’s density is about 1.33 grams per cubic centimeter, and Earth’s is 5.51 grams per cubic centimeter“, reveals Khalid Barkaoui.
“The planet is so light that it is difficult to think of an analogous solid material. adds Julien de Wit, professor at MIT and co-author of the study, in a press release. “The reason it looks like cotton candy is that both are mostly made of air. The planet is light and fluffy.”
Read also:Discovery of a new “cotton candy” planet in the Milky Way
“WASP-193b is a cosmic mystery”
WASP-193b is the second least dense planet discovered to date, after the significantly smaller Kepler-51d. “It cannot be reproduced by our standard models of irradiated gas giants, even under the unlikely hypothesis of a coreless structure.“, remarks Khalid Barkaoui.
The planet would be made primarily of hydrogen and helium, like most other gas giants in the galaxy. But the particularity of WASP-193b would be the extreme expansion of its gas envelope. It could be explained by a significant deposit of energy in the depths of the planet, but the details of the mechanism are not yet understood.
“At the moment, we cannot explain either the structure or the formation of such a planet. WASP-193b is a cosmic mystery. Solving it will require both observational and theoretical work, including measurement of the planet’s atmospheric properties with the James Webb Space Telescope (JWST), and their confrontations with different theoretical mechanisms likely to lead to such extreme inflation”concludes Khalid Barkaoui.
Also read:First observation of gas giant planets forming by gravitational collapse of a cloud of gas and dust
