An international team of astronomers has discovered a giant planet with an extremely low density, similar to that of cotton candy.
This new planet, named WASP-193b, was found by researchers from the EXOTIC Laboratory at the University of Liège, in collaboration with MIT and the Astrophysics Institute in Andalusia.
The planet orbits a distant sun-like star 1,200 light-years from Earth.
WASP-193b is a remarkable find. It is 50% larger than Jupiter but seven times less massive, giving it an extremely low density.
“WASP-193b is the second least dense planet discovered to date, after Kepler-51d, which is much smaller,” explains Khalid Barkaoui, a postdoctoral researcher at ULiège’s EXOTIC Laboratory and the lead author of the study published in Nature Astronomy.
“Its extremely low density makes it a real anomaly among the more than five thousand exoplanets discovered to date.”
The discovery began with data from the Wide Angle Search for Planets (WASP), an international collaboration that operated two robotic observatories.
These observatories used wide-angle cameras to monitor the brightness of thousands of stars. Between 2006 and 2008, and again from 2011 to 2012, the WASP-South observatory detected periodic dips in light from the star WASP-193.
These dips indicated that a planet was passing in front of the star every 6.25 days.
The team then used the TRAPPIST-South and SPECULOOS-South observatories, located in the Atacama Desert in Chile, to measure the planetary signal in different wavelengths and confirm that the object was indeed a planet.
They also used spectroscopic observations from the HARPS and CORALIE spectrographs in Chile to measure the planet’s mass.
To their surprise, the measurements revealed that WASP-193b has an extremely low density. The planet’s mass is only 0.14 times that of Jupiter, while its size is 1.5 times that of Jupiter.
This gives it a density of about 0.059 grams per cubic centimeter.
In comparison, Jupiter’s density is about 1.33 grams per cubic centimeter, and Earth’s density is 5.51 grams per cubic centimeter. Cotton candy, which has a density of about 0.05 grams per cubic centimeter, is one of the few materials with a similar density to WASP-193b.
“The planet is so light that it’s difficult to think of an analogous, solid-state material,” says Julien de Wit, a professor at MIT and co-author of the study.
“The reason why it’s close to cotton candy is because both are pretty much air. The planet is basically super fluffy.”
The researchers believe that WASP-193b is made mostly of hydrogen and helium, like most other gas giants.
However, in the case of WASP-193b, these gases form a hugely inflated atmosphere that extends tens of thousands of kilometers beyond what is seen in Jupiter. Exactly how a planet can inflate so much remains a mystery.
Current planetary formation theories cannot explain it, as it would require a significant amount of energy to be deposited deep into the planet’s interior.
“We don’t know where to place this planet within our current formation theories, because it’s an outlier to all of them,” says Francisco Pozuelos, an astronomer at the Instituto de Astrofisica de Andalucia.
“We cannot explain how this planet was formed. Studying its atmosphere more closely will help us understand its evolutionary path.”
Source: KSR.
