Astronomers from MIT and the University of Liège in Belgium, along with international collaborators, have discovered a fascinating exoplanet—an enormous yet wispy gas giant orbiting a star in our Milky Way. This discovery could provide critical insights into the enigma of how such lightweight, oversized planets form.
Named WASP-193b, this planet outshines Jupiter in size but pales in density. Researchers found that WASP-193b is 50% larger than Jupiter but only one-tenth as dense, giving it a nearly impossible low density similar to cotton candy.
WASP-193b: The Fluffiest Exoplanet
Among the over 5,400 exoplanets identified so far, WASP-193b stands out as one of the most airy. It is the second least dense planet ever discovered, second only to Kepler-51d, a smaller, Neptune-sized world. However, its massive size and fluffy nature set it apart, akin to a planet-sized marshmallow drifting through space.
“Finding giant planets with such incredibly low density is extremely rare,” explains Khalid Barkaoui, lead author of the study and a postdoctoral researcher at MIT. “There’s a class known as puffy Jupiters, and for 15 years, scientists have puzzled over them. WASP-193b is a prime example of this category.”
“We have no idea where to fit this planet into our current formation theories—it doesn’t match any of them,” adds Francisco Pozuelos, co-lead author and senior researcher at the Institute of Astrophysics of Andalusia in Spain. “Existing models of planetary evolution can’t account for something like this. Analyzing its atmosphere more closely might help us figure out how such an oddball came to be.”
The research team from MIT includes Julien de Wit, an assistant professor in MIT’s Department of Earth, Atmospheric, and Planetary Sciences, and postdoctoral researcher Artem Burdanov. They worked with collaborators across Europe to unravel the mystery of WASP-193b.
A Cosmic Curveball
The planet first drew attention through the Wide Angle Search for Planets (WASP), a network of robotic observatories operating on both hemispheres. These observatories monitor the brightness of numerous stars, searching for signs of planets. WASP-193b seemed like a giant marshmallow floating among the stars, posing a unique challenge to astronomers.
A Planet on the Puffy Side
The research team confirmed WASP-193b’s astonishing lightness. They calculated its mass to be 14% of Jupiter’s, with a density of just 0.059 grams per cubic centimeter, almost entirely air compared to other planets. For comparison, Jupiter’s density is 1.33 grams per cubic centimeter, and Earth’s is significantly higher, at 5.51 grams per cubic centimeter. WASP-193b’s density is closer to cotton candy, which weighs approximately 0.05 grams per cubic centimeter.
A Giant Balloon of a Planet
Scientists believe WASP-193b is primarily composed of hydrogen and helium, like other gas giants. However, it has an unusually extended atmosphere, potentially stretching tens of thousands of kilometers beyond Jupiter’s own. Exactly how a planet can swell this much while remaining so lightweight remains a mystery that current planetary formation theories cannot explain.
To gather a clearer understanding of this celestial balloon, the research team plans to use a technique developed by Julien de Wit, which will help determine atmospheric properties like temperature, composition, and pressure at various depths. These measurements will refine the planet’s exact mass.
For now, WASP-193b remains exclusively out of our reach. Though it might seem appealing, the idea of consuming a planet wrapped in cosmic cotton candy is beyond our capabilities—yet another intriguing phenomenon in the vast cosmos.
This discovery underscores the incredible complexity and variety of worlds beyond our solar system, encouraging further exploration and study. As we continue to unveil these cosmic puzzles, we inch closer to understanding the universe in all its vastness and mystery.
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