Lemon Shaped Jupiter-Sized Planet Discovered

Earth, Laniakea Supercluster—When the universe gives you lemons, apparently its literal.

Somewhere about 2,000 light-years from Earth, a Jupiter-sized object is being pulled like cosmic taffy around a spinning dead star. Its year lasts less than eight hours. It probably has clouds made of soot. And deep inside, crushing pressures may be forging diamonds from pure carbon.

It also sometimes looks like a lemon.

PSR J2322-2650b is the most stretched-out exoplanet ever confirmed, and it’s confounding astronomers scrambling to explain how anything like it could exist.
The discovery, published December 16 in The Astrophysical Journal Letters, comes from observations using NASA's James Webb Space Telescope (JWST). The planet's equatorial diameter stretches about 38 percent wider than its polar diameter, giving it the appearance of an American football being slowly squeezed by gravity.

"It's the stretchiest planet that we've confirmed the stretchiness of," lead author Michael Zhang, an exoplanet scientist at the University of Chicago, told The New York Times.

The planet orbits a pulsar, the rapidly spinning corpse of a massive star that died in a supernova, and now emit regular beams of radiation like cosmic lighthouses. Pulsars are extraordinarily dense, packing the mass of the Sun into something roughly the size of a city. The so-called Lemon Planet sits just one million miles from this stellar remnant, compared to Earth's 93 million miles from the Sun, according to NASA.

But the shape is just the start. When researchers analyzed the planet's atmosphere, they found something unprecedented.

"This was an absolute surprise," said study co-author Peter Gao of the Carnegie Earth and Planets Laboratory. "I remember after we got the data down, our collective reaction was 'What the heck is this?' It's extremely different from what we expected."

Instead of the water, methane, and carbon dioxide typically found on gas giants, the atmosphere is dominated by helium and molecular carbon; elements bound only to themselves, with no oxygen or nitrogen in sight. That's never been observed on any exoplanet before, according to the University of Chicago research team. This causes floating soot clouds in the upper atmosphere and, potentially, diamonds forming deep below.

Even the planet's origin story is a mystery. One theory suggests it might be the last remnants of a star that's been slowly devoured by its pulsar companion, dubbed a "black widow" system. Another possibility is stranger still.

"I'm open to the possibility that this is an entirely new type of object," Zhang told Scientific American.

For now, PSR J2322-2650b is the only known gas giant orbiting a pulsar, the only confirmed world with a carbon-helium atmosphere, and the most gravitationally distorted planet ever studied.

Whether it represents the dying breath of a cannibalized star or something entirely new, one thing is certain: if the universe hands you a lemon, don't make lemonade — point a $10 billion telescope at it.