Kepler-51d, a planet so light it resembles cotton candy in density, is wrapped in the thickest layer of atmospheric haze ever detected on a world — and even the James Webb Space Telescope cannot see through it.
A team led by Penn State researchers used JWST to study the so-called “super-puff” planet, which sits roughly 2,615 light years away in the constellation Cygnus. According to the announcement, the haze may be one of the largest ever found on any planet, potentially stretching as wide as Earth itself — making it nearly impossible to identify what the atmosphere is made of or trace how the planet came to be.
The findings were published March 16 in the Astronomical Journal.
A System That Breaks the Rules
Kepler-51 hosts four known planets, at least three of which belong to the ultra-low-density super-puff class. These worlds are comparable in size to Saturn but carry only a few times the mass of Earth. Kepler-51d is the coolest and least dense of the group.
“We think the three inner planets orbiting Kepler-51 have tiny cores and huge atmospheres giving them a density akin to cotton candy,” said Jessica Libby-Roberts, first author of the paper and now an assistant professor of physics and astronomy at the University of Tampa. “These ultra-low-density super-puff planets are rare, and they defy conventional understanding of how gas giants form. And if explaining how one formed wasn’t difficult enough, this system has three!”
Standard models hold that gas giants build dense cores first, then use gravity to accumulate thick gas envelopes — typically far from their host star, in conditions similar to where Jupiter and Saturn formed. Kepler-51d fits none of that. It appears to lack a dense core and orbits at a distance from its star roughly comparable to Venus’s position in our solar system.
What the Haze Is Blocking
Because the planet is too distant for direct imaging, researchers rely on transit observations — watching starlight filter through the atmosphere as the planet crosses in front of its star. That filtered light normally carries a chemical fingerprint. Here, the haze absorbs and scatters that signal before it can be read.
Identifying those atmospheric chemicals would offer clues to where and how the planet originally formed — precisely the information the haze is withholding.
The host star adds another layer of difficulty. “Kepler-51 is a relatively active star, and its stellar winds should easily blow away the gasses from this planet, though the extent of this mass-loss over Kepler-51d’s lifetime remains unknown,” Libby-Roberts said. One possibility the team considers is that the planet formed further out and migrated inward, but the mechanics behind that — and why the same system produced three such outliers — remain unresolved.
“What is it about this system that created these three really oddball planets, a combination of extremes that we haven’t seen anywhere else?” she said.
The haze that was supposed to yield answers has so far produced only more questions about one of the stranger planetary systems yet found.
Photo by Jeremy Müller on Pexels
This article is a curated summary based on third-party sources. Source: Read the original article
