Discovery of a very thin ‘cotton candy’ exoplanet shocks scientists – ‘We can’t explain how this planet formed’

Astronomers have discovered a massive, low-density planet called WASP-193b, which is 50% larger than our planet. Jupiter But it has a density similar to cotton candy. This discovery challenges current planetary formation theories, as scientists cannot explain how such a planet would form.

Astronomers have discovered a huge, fluffy alien ball of a planet orbiting a distant star in our galaxy milky way galaxy. The discovery was reported on May 14 in the journal Nature astronomy By researchers from Massachusetts Institute of TechnologyThe discovery, made at the University of Liège in Belgium and elsewhere, is a promising key to the mystery of how these ultra-light giant planets form.

The new planet, called WASP-193b, appears to be a dwarf the size of Jupiter, yet its density is a fraction of its density. Scientists found that the gas giant is 50% larger than Jupiter, and about a tenth as dense, which is very low, similar to the density of cotton candy.

WASP-193b is the second lightest planet yet discovered, after the smallest, Neptune-Like the World, Kepler 51d. The new planet’s much larger size, combined with its extremely light density, makes WASP-193b something of an outlier among the more than 5,400 planets discovered so far.

“Finding these giant objects with such small densities is really very rare,” says Khaled Al-Barqawi, the study’s lead author and a postdoctoral researcher at MIT. “There’s a class of planets called puffy Jupiters, and they’ve been a mystery for 15 years now as to what they are. This is an extreme case of that class.

“We don’t know where to put this planet in all the formation theories we have now, because it’s an anomaly in all of them,” adds co-lead author Francisco Pozuelos, a senior researcher at the Institute of Astrophysics in Andalusia. In Spain. “We cannot explain how this planet formed based on classical evolutionary models. Looking closely at its atmosphere will allow us to obtain an evolutionary path for this planet.”

Co-authors of the MIT study include Julian de Wit, an assistant professor in MIT’s Department of Earth, Atmospheric and Planetary Sciences, and Artem Burdanov, a postdoctoral researcher at MIT, along with collaborators from multiple institutions across Europe. .

Artist’s impression of the WASP-193b system. Credit: University of Liège

“Interesting development”

The new planet was initially spotted by the Wide Angle Search for Planets Project, or WASP, an international collaboration between academic institutions that together operate two robotic observatories, one in the northern hemisphere and one in the southern. Each observatory uses an array of wide-angle cameras to measure the brightness of thousands of individual stars across the entire sky.

In surveys conducted between 2006 and 2008, and again from 2011 to 2012, the WASP-South Observatory detected periodic transits, or dips in light, of WASP-193, a bright, nearby Sun-like star located 1,232 years away. light from Earth. Astronomers determined that the periodic dips in the star’s brightness were consistent with a planet orbiting the star and blocking its light every 6.25 days. Scientists measured the total amount of light the planet blocked with each transit, giving them an estimate of the giant planet’s size, about the size of a super-Jupiter.

Next, astronomers looked to determine the planet’s mass, a measure that would then reveal its density and perhaps also clues to its composition. To get a mass estimate, astronomers typically use radial velocity, a technique by which scientists analyze the star’s spectrum, or different wavelengths of light, as the planet orbits the star. A star’s spectrum can change in specific ways depending on what attracts the star, such as the planet it orbits. The more massive a planet is, and the closer it is to its star, the more its spectrum shifts — a distortion that can give scientists an idea of ​​the planet’s mass.

For WASP-193 b, astronomers obtained additional high-resolution spectra of the star taken by various ground-based telescopes, and tried to use the radial velocity to calculate the planet’s mass. But it kept coming up empty, precisely because, as it turned out, the planet was too light to be detected on its star.

“Usually, large planets are very easy to detect, because they are usually massive, and they exert a large impact on their star,” De Wit explains. “But what was difficult about this planet was that, although it was huge, its mass and density were so low that it was very difficult to detect using just the radial velocity technique. It was an interesting development.”

“[WASP-193b] “It’s so mild that it took four years to collect data and show that there was a mass signal, but it’s actually very small,” Barqawi says.

“We were initially getting very low densities, and it was very hard to believe at first,” Buzuelos adds. “We repeated the process of analyzing all the data several times to make sure that this was the true density of the planet because it was so rare.”

An inflated world

Ultimately, the team confirmed that the planet was indeed very light. They calculated that its mass was about 0.14 that of Jupiter. Its density, derived from its mass, was about 0.059 grams per cubic centimeter. In contrast, Jupiter’s weight is about 1.33 grams per cubic centimeter; Earth is 5.51 grams per cubic centimeter larger. Perhaps the substance closest in density to the new puffy 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 think of comparable solid matter,” says Barqawi. “The reason it’s close to cotton candy is because both are made mostly of light gases rather than solids. The planet is basically very thin.”

Researchers suspect that the new planet is composed mostly of hydrogen and helium, like most other gas giants in the galaxy. For WASP-193b, these gases likely form an extremely puffy atmosphere extending tens of thousands of kilometers beyond Jupiter’s atmosphere. How a planet could bloat to such an extent and still maintain such an extreme light density is a question that no existing theory of planetary formation can yet answer.

To get a better picture of the new thin world, the team plans to use a previously developed D-Wit technique to first derive certain properties of the planet’s atmosphere, such as its temperature, composition and pressure at different depths. These properties can then be used to accurately calculate the planet’s mass. For now, the team sees WASP-193b as an ideal candidate for follow-up study by observatories such as WASP-193b James Webb Space Telescope.

“The larger the atmosphere of a planet, the more light can pass through it,” says de Wit. “So this planet is clearly one of the best targets we have for studying atmospheric effects. It will serve as a Rosetta Stone for trying to solve the mystery of bulging Jupiters.”

Reference: “An extended, low-density atmosphere around the Jupiter-sized planet WASP-193 b” by Khaled Al-Barqawi, Francisco J. Bozuelos, Coyle Hillier, Barry Smalley, Louise D. Nielsen, Prajwal Niraula, Michael Gillon, Julian de Wit, Simon Müller, Caroline Dorn, Ravit Held, Emmanuel Jehin, Brice Olivier Demaure, Valérie van Grootel, Abderrahmane Sepkew, Mourad Ghashoui, David. Anderson, Zuhair Ben Khaldoun, François Bouchy, Artem Bordanov, Leticia Delris, Elsa Ducrot, Leonel Garcia, Abdelhadi Al Jabri, Monica Lindell, Pierre F. L. Maxted, Catriona A. Murray, Peter Bellman Pedersen, Didier Kilo, Daniel Sebastian, Oliver Turner, Stefan Audrey, Mathilde Timmermans, Amaury H. M. G. Triode, and Richard G. West, May 14, 2024, Nature astronomy.
DOI: 10.1038/s41550-024-02259-y

This research was funded, in part, by the University Association and the UK Science and Technology Facilities Council for WASP; European Research Council; Wallonia-Brussels Union; and the Heising-Simons Foundation, Colin and Leslie Masson, and Peter A. Gilman, who support Artemis and other SPECULOOS telescopes.