Researchers at the University of Liège have identified WASP-193b, an exoplanet with an exceptionally low density comparable to cotton candy. This super-fluffy gas giant is significantly larger than Jupiter but possesses only a fraction of its mass, presenting a major challenge to existing theories of planetary evolution.
TLDR: Astronomers have discovered WASP-193b, an exoplanet with a density so low it resembles cotton candy. Located 1,200 light-years away, this gas giant is 50% larger than Jupiter but seven times less massive. The discovery forces scientists to rethink how such super-puff planets form and maintain their massive atmospheres.
Astronomers at the University of Liège, working alongside an international consortium, have unveiled the discovery of WASP-193b, an extraordinary exoplanet with a density so remarkably low that it has been likened to cotton candy. Located approximately 1,200 light-years from Earth, this “super-puff” planet represents one of the most extreme instances of planetary inflation ever documented. The research, published in the journal Nature Astronomy, highlights a celestial body whose physical properties fundamentally challenge our current understanding of how gas giants form and evolve.
WASP-193b orbits a Sun-like star with a period of just 6.25 days. While the planet’s volume is roughly 50 percent greater than that of Jupiter, its mass is significantly lower—only about one-seventh of Jupiter’s mass. This discrepancy leads to a calculated density of approximately 0.059 grams per cubic centimeter. To put this into perspective, Jupiter has a density of 1.33 grams per cubic centimeter, while Earth’s density is a much higher 5.51 grams per cubic centimeter. Cotton candy, by comparison, has a density of about 0.1 grams per cubic centimeter, meaning WASP-193b is actually lighter and fluffier than the sugary treat found at carnivals.
The identification of this anomalous world was made possible through the Wide Angle Search for Planets (WASP) project, which utilizes a network of robotic telescopes to monitor the brightness of stars. The initial detection used the transit method, observing the slight dip in starlight as the planet passed in front of its host star. To confirm the planet’s mass and density, the team employed radial velocity measurements from the HARPS and CORALIE spectrographs located at the European Southern Observatory in Chile. These precision instruments measure the “wobble” of the star caused by the planet’s gravitational pull. In the case of WASP-193b, the signal was so faint due to the planet’s low mass that it required years of meticulous data collection.
Lead researcher Khalid Barkaoui and his colleagues at the University of Liège’s EXOTIC laboratory spent considerable time validating these findings. The extreme nature of WASP-193b makes it a significant outlier even among the rare class of “puffy” planets. Most gas giants possess a substantial solid core and a thick atmosphere held together by gravity. However, WASP-193b appears to be composed almost entirely of hydrogen and helium, resulting in an atmosphere that is immensely bloated.
Current theories of planetary evolution are struggling to account for such a state. While it is known that intense radiation from a nearby star can cause a planet’s atmosphere to expand, the degree of inflation seen in WASP-193b exceeds the limits of existing models. The energy required to maintain such a low density over billions of years is far greater than what standard astrophysical simulations currently predict. This suggests that there are unknown mechanisms at play in the heating of planetary interiors or the retention of massive, light atmospheres.
The discovery offers a premier opportunity for atmospheric characterization. Because the planet has such an extended and translucent atmosphere, starlight can pass through its gaseous layers more easily than it would through a denser world. This makes WASP-193b an ideal candidate for follow-up observations with the James Webb Space Telescope (JWST). By studying the filtered light, astronomers hope to map the chemical composition and temperature of the atmosphere. Such data could reveal the secrets of how this “cotton candy” world came to be and how it survives so close to its star.
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