Moroccan astronomer and researcher Khalid Barkaoui and his team have revealed the discovery of an exceptionally lightweight planet, the size of massive Jupiter, orbiting a distant star, according to research published in the journal Nature Astronomy on Tuesday.
The new planet, named WASP-193b, is one and half times larger than Jupiter, but has a density only about one-tenth of the great planet, giving this new gaseous giant the appearance of cotton candy.
WASP-193b is the second lightest planet discovered to date, after Neptune. The combination of large size and extremely low density makes it an outlier among the more than five thousand exoplanets discovered so far.
Berkaoui, the lead astronomer behind this revolutionary discovery, said “WASP-193b is one of the most unusual exoplanets discovered so far. Its ultra-low density does not match traditional models of radioactive gas giants, even under the assumption of no nucleus.”
The team’s discoveries are based upon data collected by the Wide Angle Search for Planets (WASP), an international collaboration of academic institutions operating robotic observatories in the northern and southern hemispheres. These observatories use wide-angle cameras to observe the brightness of thousands of stars in the sky.
Observations made between 2006 and 2008, and again between 2011 and 2012, by the WASP-South Observatory revealed periodic transits of WASP-193, a Sun-like star located 1,200 light-years from Earth. These transits, characterized by a decrease in brightness, were determined to correspond to the passage of a planet in front of the star every 6.25 days.
To determine the nature of the planetary interceptor, the researchers used the TRAPPIST-South and SPECULOOS-South observatories located in the Atacama Desert in Chile. In addition, spectroscopic observations from the HARPS and CORALIE spectrometers in Chile were used to determine the mass of the planet.
The accumulation of data revealed an unparalleled density for WASP-193b. With a mass roughly equivalent to 0.14 times the mass of Jupiter and a volume equivalent to 1.5 times the size of Jupiter, the planet’s density was calculated to be about 0.059 grams per cubic centimeter, comparable to the density of spun sugar in the children’s confection cotton candy.
Julien de Wit, a co-author from MIT, noted, “The lightweight nature of the planet makes it difficult to compare with a solid. The resemblance to cotton candy is due to its main gas composition, which makes the planet super soft.”
Researchers speculate that WASP-193b is composed mainly of hydrogen and helium, similar to most gas giants in the galaxy. These gases likely form an enormously inflated atmosphere that surrounds the planet, extending more than tens of thousands of kilometers beyond the planet’s own atmosphere. However, the mechanism driving the inflation of the planetary mass remains a mystery.
“WASP-193b is an intriguing puzzle,” concludes Khaled Barakaoui. “Solving it will require additional observational and theoretical investigations, including using the James Webb Space Telescope to measure its atmospheric properties and compare them to the various theoretical mechanisms responsible for such extreme inflation.”
“This is not the first time that unprecedented new discoveries have been made through the participation of researchers from the Oukaimeden Observatory,” Zouhair Ben Khaldoun, Director of the Observatory of the Cadi Ayyad University, remarked. “It’s a testament to the scientific dynamism of this unique institution at the regional level.”
The discovery of this exceptionally light planet was made possible by Berkaoui’s doctoral research while a former student at the University of El Cadi Ayyad and Oukaimeden Observatory, under the supervision of Ben Khaldoun.
Berkaoui presented his dissertation at the University of El Cadi Ayyad on September 8, 2020, entitled, “Detection and characterization of exoplanets in transit using the Trappist-North telescope.”
Berkaoui is currently a postdoctoral researcher at the University of Liège and the Astronomical Institute of the Canary Islands.