A lemon-shaped exoplanet is squeezing what we know about planet formation

In a zesty new discovery, scientists have unearthed a strange lemon-shaped exoplanet. It is unlike one we have seen before, challenging many of the previously held assumptions about planetary formations and atmospheres.

When space gives you lemons

The exoplanet, which has been called PSR J2322-2650b, was found using NASA’s James Webb telescope. It has properties that are in “stark contrast to every known exoplanet orbiting a main-sequence star,” said a study published in The Astrophysical Journal Letters. PSR J2322-2650b “blurs the line between planets and stars,” and “how the planet came to be is a mystery,” said a release by the University of Chicago.

The exoplanet is about the mass of Jupiter and is “known to orbit a pulsar, a rapidly spinning neutron star,” said NASA. A pulsar “emits beams of electromagnetic radiation at regular intervals typically ranging from milliseconds to seconds” that can “only be seen when they are pointing directly toward Earth, much like beams from a lighthouse.” They are essentially highly dense remnants of dead stars left behind after they explode in a supernova.

“The planet orbits a star that's completely bizarre — the mass of the sun, but the size of a city,” Michael Zhang, a postdoctoral researcher at the University of Chicago and a coauthor of the study, said in the release. PSR J2322-2650b is extraordinarily close to its star at just 1 million miles away, compared to the Earth’s distance from the sun, which is about 100 million miles. The tight orbit means that the exoplanet takes only 7.8 hours to go around its star. Also, because PSR J2322-2650b is “big enough and close enough to its pulsar host, the star’s gravity is pulling the planet into a lemon shape,” said Scientific American.

What has interested scientists most is the planet’s atmosphere, which “nobody has ever seen before,” said Zhang. “Instead of finding the normal molecules we expect to see on an exoplanet — like water, methane and carbon dioxide — we saw molecular carbon, specifically C3 and C2,” said Zhang. PSR J2322-2650b’s atmosphere is “dominated by helium and carbon, and likely has clouds of carbon soot that condense to create diamonds that rain down onto the planet,” said Space.com (a sister site of The Week). “Everywhere in the universe, where there’s carbon, there tends to be nitrogen and oxygen,” Zhang said to Scientific American.

Find how they’re made

All these cosmic anomalies raise questions as to how PSR J2322-2650b formed in the first place. While designated as an exoplanet, some theorize that the planet is “itself the stripped remains of a former star” because of its strange composition, said Scientific American. But “that doesn’t solve the missing oxygen and nitrogen mystery.” In this case, the star and exoplanet together can be called a “black widow system,” which is a “rare type of double system where a rapidly spinning pulsar is paired with a small, low-mass stellar companion,” said NASA. In it, the pulsar “erodes and devours” the companion with its “jets of radiation,” said Space.com.

If the planet is truly a black widow system, we may have witnessed the “very last moments” with PSR J2322-2650b “on the cusp of being entirely consumed,” said The New York Times. There is also a chance that it is something different altogether. “Did this thing form like a normal planet? No, because the composition is entirely different,” said Zhang. “Did it form by stripping the outside of a star, like ‘normal’ black widow systems are formed? Probably not, because nuclear physics does not make pure carbon.”