Lemon-Shaped Planet PSR J2322-2650b: The Universe’s Most Stretched-Out World
Earth isn’t a perfect sphere; its rotation causes a slight bulge at the equator, making it only about 0.3% wider than the distance from pole to pole. But the newly studied PSR J2322-2650b puts Earth’s modest shape distortion to shame. This Jupiter-mass object, observed by the James Webb Space Telescope, has an equatorial diameter about 38% wider than its polar diameter, giving it an unmistakable lemon-like shape.
“This is the stretchiest planet we’ve confirmed,” said Michael Zhang, an exoplanet scientist at the University of Chicago and lead author of a study published in The Astrophysical Journal Letters.
Discovered in 2011 by Australia’s Parkes radio telescope, PSR J2322-2650b orbits a pulsar—an extremely dense, fast-spinning star left behind after a supernova—located over 2,000 light-years from Earth. Remarkably, this gas giant circles the pulsar at a distance of just one million miles, completing an orbit in roughly eight hours. It is currently the only known gas giant in orbit around a pulsar, according to The NYT.
The planet’s extreme shape arises from the pulsar’s intense gravitational pull. “Material is literally being funneled from the planet to the pulsar,” explained Peter Gao, an exoplanet scientist at the Carnegie Institution for Science and co-author of the paper. “There’s even a pointed tip where matter spirals off the planet toward the star.”
Infrared observations by Webb allowed the team to analyze the planet’s unusual atmosphere, a first for a pulsar-orbiting object. Surprisingly, the planet lacks hydrogen, oxygen, and nitrogen, instead consisting primarily of helium and molecular carbon. “A helium- and carbon-dominated world is unlike anything we’ve seen before,” Gao said. The carbon-rich atmosphere may form graphite clouds and a diamond core, with storm bands tracing the lemon-shaped contours and a reddish hue caused by carbon dust.
Some researchers suggest PSR J2322-2650b may not be a traditional planet at all but a remnant of a star gradually consumed by the pulsar, possibly a late-stage black widow system. “It might have lost 99.9% of its mass, and we just caught it at the very end,” Gao noted.
Alternatively, Zhang speculates it could represent a completely new type of long-lasting object orbiting a pulsar. “We hope to find similar worlds for comparison. If it’s steadily losing mass, observing it now could be incredibly lucky,” he said.
Either way, PSR J2322-2650b challenges our understanding of planetary formation and demonstrates the bizarre variety of objects the universe can produce.
