Astronomers have discovered a strange lemon-shaped planet that doesn’t make sense. A Jupiter-sized world orbiting a dead star has an atmosphere whose spectrum is dominated by carbon molecules, with a composition so extreme it has left scientists searching for an explanation of how such an object could form.
PSR J2322-2650b (the strange planet) circles a pulsar (the ultra-dense, rapidly spinning core left behind after a massive star explodes) every 7.8 hours. The pulsar blasts it with gamma rays, a form of high-energy radiation higher-energy than X-rays, that likely heat the atmosphere to temperatures reaching 1,900 Kelvin (about 2,960 degrees Fahrenheit).
Using the James Webb Space Telescope to observe the entire orbit, researchers found molecular carbon dominating the spectrum so completely that oxygen, nitrogen, and hydrogen (elements typically abundant in planetary atmospheres) appear strongly depleted or weren’t clearly detected.
The carbon-to-oxygen ratio exceeds 100. The carbon-to-nitrogen ratio tops 10,000. No known planet orbiting a normal star, and no current theory about how pulsar companions form, can explain these numbers.
“The planet orbits a star that’s completely bizarre — the mass of the Sun, but the size of a city,” explained the University of Chicago’s Michael Zhang, the principal investigator on this study, in a statement. “This is a new type of planet atmosphere that nobody has ever seen before.”
An Atmosphere Built From Carbon Chains
When light passes through the planet’s atmosphere, different molecules absorb specific colors. By analyzing which colors are missing, astronomers can identify what molecules are present. In this case, the spectrum revealed molecules rarely seen in planetary atmospheres: C3 (three carbon atoms bonded together) and C2 (two carbon atoms).
These carbon chains absorbed light at specific wavelengths (particular colors in the infrared, invisible to human eyes). C3 showed up as a sudden drop at 3.014 microns, in the infrared beyond human vision. C2 created a sawtooth pattern between 2.45 and 2.85 microns. Additional absorption features suggested the presence of carbon-hydrogen bonds, though the exact molecules remain uncertain.
To understand how unusual this is, consider what should happen in a hot atmosphere. Carbon and oxygen atoms strongly prefer to bond together, forming carbon monoxide. The only way to have more molecular carbon than carbon monoxide is if carbon outnumbers oxygen by huge amounts—in this case, by more than 2,000 to one. Similarly, carbon and nitrogen should bond together unless carbon outnumbers nitrogen by more than 10,000 to one.
“The extreme carbon enrichment poses a severe challenge to the current understanding of ‘black-widow’ companions, which were expected to consist of a wider range of elements due to their origins as stripped stellar cores,” the researchers wrote.
How Black Widows Form, And Why This One Breaks the Rules
Black widow systems get their name from spiders that eat their mates. In space, a pulsar slowly destroys its companion star. The pulsar’s intense radiation and gravitational pull tear away the star’s outer layers, eventually leaving behind a small, dense remnant.
This process should produce an object made mostly of helium if the stripping happens early enough, before the star begins converting helium into carbon in its core through nuclear fusion. The remnant should contain whatever elements existed in the star’s core at that moment, typically a mix of helium, carbon, nitrogen, and oxygen in moderate ratios.
PSR J2322-2650b doesn’t fit this picture. The researchers explored alternative explanations, each with its own problems.
Some rare stars show elevated carbon levels, with carbon-to-oxygen ratios reaching 12 to 81. While higher than typical stars, these values still fall far short of what this planet displays.
Other aging stars convert helium into carbon through a nuclear process, creating what astronomers call “carbon stars.” These reach carbon-to-oxygen ratios of only several. They produce carbon-rich dust in their outflows, offering another potential carbon source. However, the mechanism for concentrating that dust into a Jupiter-mass planet with such extreme ratios remains unclear.
In one illustrative model, the planet consists mostly of helium with roughly 1% carbon by mass in its interior. A planet made entirely of carbon would be much smaller and denser than what observations show—about one-third Jupiter’s radius instead of roughly matching it. But if the planet is mostly helium inside, what process concentrated so much carbon in the atmosphere we can see?
Gamma-Ray Heat and Westward Winds
The planet’s heating differs from anything seen on worlds orbiting normal stars. Gamma rays likely penetrate deep into the atmosphere instead of warming just the surface layers the way visible sunlight does on Earth.
In the models, these high-energy photons deposit their energy at a depth where the pressure reaches about 10 bars—roughly 10 times the air pressure at sea level on Earth. This deep heating drives the planet’s wind patterns differently than on normal hot Jupiters (giant planets orbiting close to their stars).
The researchers tracked how the planet’s light shifted to bluer or redder wavelengths as it moved toward or away from Earth in its orbit. From these measurements, they determined the planet orbits at a tilt of 31 degrees (imagine tilting a hula hoop from flat by about one-third of a right angle) and has a mass between 1.4 and 2.4 times Jupiter’s mass.
The temperature structure shows dramatic day-night contrasts. The nightside maintains a relatively uniform 900 Kelvin (about 1,160 degrees Fahrenheit) with a smooth spectrum, suggesting either consistent temperature throughout that side or a thick cloud deck blocking our view. The dayside reaches 2,300 Kelvin (about 3,680 degrees Fahrenheit) at its hottest points.
Surprisingly, the hottest spot doesn’t line up with the point facing the pulsar. Instead, the temperature peak appears shifted westward by about 12 degrees, indicating powerful winds blowing opposite to the planet’s rotation direction.
Computer models of rapidly rotating planets predict exactly this behavior. Most hot Jupiters orbiting normal stars have winds flowing eastward around their equators, like a jet stream. But when a planet spins faster than once every 10 hours or so, the pattern flips. Westward winds dominate away from the equator. PSR J2322-2650b offers strong evidence consistent with this predicted pattern.
Source : https://studyfinds.org/unprecedented-lemon-shaped-planet-found/
