An international team of scientists, led by astronomer Khalid Barkaoui, has unveiled the existence of an exceptionally lightweight planet orbiting a distant star. This groundbreaking discovery was recently published in the journal Nature Astronomy.

The unveiling of this discovery originates from the doctoral research conducted by Khalid Barkaoui, a doctoral candidate at Cadi Ayyad University and the Oukaimeden Observatory, under the guidance of Zouhair Benkhaldoun, Director of the Oukaimeden Observatory. Khalid Barkaoui successfully defended his doctoral thesis at Cadi Ayyad University on September 8, 2020, with the dissertation titled: ""Detection and characterization of exoplanets in transit with the TRAPPIST-North telescope."" Currently, he serves as a postdoctoral researcher at the University of Liège and the Instituto de Astrofísica de Canarias.

The newfound planet, named WASP-193b, boasts dimensions surpassing those of Jupiter while maintaining a density merely a fraction of its magnitude. Researchers have determined that this gas giant exceeds Jupiter's size by 50 percent yet exhibits a density approximately one-tenth of Jupiter's, resulting in an extraordinarily low density comparable to that of cotton candy.

WASP-193b stands as the second lightest planet discovered to date, trailing only behind the smaller, Neptune-like super puffy planet, Kepler-51d. Its remarkable combination of substantial size and remarkably low density renders it an anomaly among the over five thousand exoplanets identified thus far.

Khalid Barkaoui, the leading astronomer behind this groundbreaking discovery, comments, ""WASP-193b is one of the most extreme exoplanets discovered to date. Its super-low-density defies conventional models of irradiated gas giants, even under the assumption of a coreless structure.""

The discovery of WASP-193b originated from data collected by the Wide Angle Search for Planets (WASP), an international collaboration of academic institutions operating robotic observatories in both the northern and southern hemispheres. These observatories utilized wide-angle cameras to monitor the brightness of thousands of stars across the sky.

Observations made between 2006 and 2008, and subsequently from 2011 to 2012, by the WASP-South observatory detected periodic transits of WASP-193, a nearby sun-like star situated 1,200 light-years from Earth. These transits, characterized by dips in brightness, were determined to align with the passage of a planet in front of the star every 6.25 days.

To validate the planetary nature of the eclipsing object, researchers employed the TRAPPIST-South and SPECULOOS-South observatories located in the Atacama Desert in Chile. Additionally, spectroscopic observations from the HARPS and CORALIE spectrographs in Chile were utilized to ascertain the mass of the planet.

The accumulation of data revealed an unprecedentedly low density for WASP-193b. With a mass approximately 0.14 times that of Jupiter and a size 1.5 times that of Jupiter, the planet's density was calculated to be about 0.059 grams per cubic centimeter—comparable to that of cotton candy.

Researchers speculate that WASP-193b predominantly consists of hydrogen and helium, akin to most gas giants in the galaxy. These gases likely form an immensely expanded atmosphere enveloping the planet, extending tens of thousands of kilometers beyond Jupiter's own atmosphere. However, the mechanism driving such extensive inflation remains elusive to existing planetary formation theories.

""WASP-193b presents a fascinating conundrum,"" said Khalid Barkaoui. ""Resolving it will necessitate further observational and theoretical investigations, notably utilizing the JWST space telescope to measure its atmospheric properties and juxtaposing them with various theoretical mechanisms potentially responsible for such extreme inflation.""

""This is not the first time that unprecedented discoveries have been made through the participation of researchers from the Oukaimeden Observatory, which attests to the scientific dynamism of this unique institution at the regional level,"" concluded Zouhair Benkhaldoun, the director of the Observatory affiliated with Cadi Ayyad University in Marrakech, Morocco.

The DOI number for the paper will be 10.1038/s41550-024-02259-y. 

Once the paper has been published online, it will be available at the following URL: https://www.nature.com/articles/s41550-024-02259-y

Contacts: 

Zouhair Benkhaldoun, Oukaimeden Observatory Director: zouhair@uca.ac.ma

Khalid Barkaoui – postdoc-ULiege:  khalid.barkaoui@uliege.be