Astronomers have discovered a huge, low-density planet named WASP-193b, which is 50% larger than Jupiter but has a density similar to cotton candy. This discovery challenges existing theories on planet formation. (Artist’s concept.) Credit: SciTechDaily.com
Astronomers have discovered a massive, low-density planet named WASP-193b, which is 50% larger than
” data-gt-translate-attributes=”({“attribute”:”data-cmtooltip”, “format”:”html”})” tabindex=”0″ role=”link”>Jupiter but has a density similar to cotton candy. This discovery challenges current theories on planetary formation, as scientists cannot explain how such a planet could form.
Astronomers have discovered a huge, strange fluffy planet orbiting a distant star in our
” data-gt-translate-attributes=”({“attribute”:”data-cmtooltip”, “format”:”html”})” tabindex=”0″ role=”link”>Milky Way galaxy. The discovery, reported on May 14 in the journal Natural astronomy by researchers from
” data-gt-translate-attributes=”({“attribute”:”data-cmtooltip”, “format”:”html”})” tabindex=”0″ role=”link”>MITthe University of Liège in Belgium and elsewhere, is a promising key to elucidating the mystery of the formation of these giant and ultra-light planets.
The new exoplanet, named WASP-193b, appears to dwarf Jupiter in size, but it is only a fraction of its density. Scientists have discovered that the gas giant is 50% larger than Jupiter and about a tenth as dense – an extremely low density, comparable to that of cotton candy.
WASP-193b is the second lightest planet discovered to date, after the smallest,
” data-gt-translate-attributes=”({“attribute”:”data-cmtooltip”, “format”:”html”})” tabindex=”0″ role=”link”>Neptune-like a world, Kepler 51d. The new planet’s much larger size, combined with its ultralight density, make WASP-193b a curiosity among more than 5,400 planets discovered to date.
“Finding these giant objects with such low density is really very rare,” says Khalid Barkaoui, lead author of the study and a postdoctoral fellow at MIT. “There is a class of planets called bloated Jupiters, and their nature has remained a mystery for 15 years now. And this is an extreme case of this class.
“We don’t know where to place this planet in all the formation theories we currently have, because it is an outlier among all of them,” adds co-lead author Francisco Pozuelos, a senior scientist at the Astrophysics Institute of Andalusia. in Spain. “We cannot explain how this planet formed, based on classical models of evolution. Taking a closer look at its atmosphere will allow us to obtain an evolutionary path of this planet.
Co-authors of the study at MIT include Julien de Wit, assistant professor in MIT’s Department of Earth, Atmospheric, and Planetary Sciences, and Artem Burdanov, postdoctoral fellow at MIT, as well as collaborators from several institutions through Europe.
Artist’s impression of the WASP-193b system. Credit: University of Liège
“An interesting twist”
The new planet was initially spotted by the Wide Angle Search for Planets, or WASP, an international collaboration of academic institutions that together operate two robotic observatories, one in the northern hemisphere and one in the southern hemisphere. Each observatory uses an array of wide-angle cameras to measure the brightness of thousands of individual stars throughout the sky.
During surveys conducted between 2006 and 2008, and again between 2011 and 2012, the WASP-South Observatory detected periodic transits, or dips in light, of WASP-193, a bright star near the Sun, located at 1,232 light years from Earth. Astronomers determined that the star’s periodic dips in brightness corresponded to a planet orbiting the star and blocking its light every 6.25 days. The scientists measured the total amount of light the planet blocked during each transit, which gave them an estimate of the giant size of the planet, super-Jupiter.
Astronomers then sought to determine the mass of the planet – a measurement which would then reveal its density and potentially also clues to its composition. To get an estimate of mass, astronomers typically use radial velocity, a technique in which scientists analyze a star’s spectrum or various wavelengths of light as a planet orbits the star. A star’s spectrum can be changed in specific ways depending on what the star is attracted to, such as an orbiting planet. The more massive a planet is and the closer it is to its star, the more its spectrum can shift — a distortion that can give scientists an idea of a planet’s mass.
For WASP-193 b, astronomers obtained additional high-resolution spectra of the star taken by various ground-based telescopes and attempted to use radial velocity to calculate the planet’s mass. But they always came up empty – precisely because, as it turned out, the planet was far too light to have any detectable pull on its star.
“In general, large planets are quite easy to detect because they are usually massive and cause a strong attraction to their star,” says de Wit. “But what was tricky about this planet is that even though it is big, enormous, its mass and density are so low that it was actually very difficult to detect it with the radial velocity technique alone. It was an interesting twist.
“(WASP-193b) is so light that it took four years to gather data and show that there is a mass signal, but it is really very small,” Barkaoui says.
“At first we were getting extremely low densities, which was very hard to believe at first,” adds Pozuelos. “We repeated the process of analyzing all the data several times to make sure this was the true density of the planet, because it was extremely rare.”
A bloated world
In the end, the team confirmed that the planet was indeed extremely light. Its mass, they calculated, was about 0.14 that of Jupiter. And its density, derived from its mass, was about 0.059 grams per cubic centimeter. Jupiter, on the other hand, weighs about 1.33 grams per cubic centimeter; and Earth is 5.51 grams per cubic centimeter. Perhaps the closest material in density to the new inflated planet is cotton candy, which has a density of about 0.05 grams per cubic centimeter.
“The planet is so light that it is difficult to imagine an analogous material in the solid state,” says Barkaoui. “The reason it’s close to cotton candy is that both are made primarily of light gases rather than solids. The planet is basically super fluffy.
Researchers suspect the new planet is made mostly of hydrogen and helium, like most other gas giants in the galaxy. For WASP-193b, these gases likely form an extremely inflated atmosphere that extends tens of thousands of kilometers farther than Jupiter’s own atmosphere. How exactly a planet can swell to this extent while maintaining ultra-light density is a question that no existing theory of planetary formation can yet answer.
To get a better picture of the fluffy new world, the team plans to use a technique previously developed by De Wit, to first infer certain properties of the planet’s atmosphere, such as its temperature, composition and pressure at different depths. These features can then be used to accurately determine the mass of the planet. For now, the team views WASP-193b as an ideal candidate for follow-up study by observatories such as the
” data-gt-translate-attributes=”({“attribute”:”data-cmtooltip”, “format”:”html”})” tabindex=”0″ role=”link”>James Webb Space Telescope.
“The larger a planet’s atmosphere, the more light can pass through it,” de Wit explains. “So it’s clear that this planet is one of the best targets we have for studying atmospheric effects.” It will be a Rosetta stone to try to solve the mystery of the inflated Jupiters.
Reference: “An extended low-density atmosphere around the Jupiter-sized planet WASP-193 b” by Khalid Barkaoui, Francisco J. Pozuelos, Coel Hellier, Barry Smalley, Louise D. Nielsen, Prajwal Niraula, Michael Gillon, Julien de Wit, Simon Muller, Caroline Dorn, Ravit Helled, Emmanuel Jehin, Brice-Olivier Demory, Valérie Van Grootel, Abderahmane Soubkiou, Mourad Ghachoui, David. R. Anderson, Zouhair Benkhaldoun, François Bouchy, Artem Burdanov, Laetitia Delrez, Elsa Ducrot, Lionel Garcia, Abdelhadi Jabiri, Monica Lendl, Pierre FL Maxted, Catriona A. Murray, Peter Pihlmann Pedersen, Didier Queloz, Daniel Sebastian, Oliver Turner, Stéphane Udry, Mathilde Timmermans, Amaury HMJ Triaud and Richard G. West, May 14 Natural astronomy.
DOI: 10.1038/s41550-024-02259-y
This research was funded, in part, by consortium universities and by the UK Science and Technology Facilities Council for WASP; the European Research Council; the Wallonia-Brussels Federation; and the Heising-Simons Foundation, Colin and Leslie Masson and Peter A. Gilman, supporting Artemis and the other SPECULOOS telescopes.