Astronomers pointed the James Webb Space Telescope at a planet circling a pulsar, watched it through a full orbit, and found an atmosphere dominated by molecular carbon, something almost never seen in a planet\u2019s air. Instead of the water, methane, and carbon dioxide that turn up again and again on other worlds, what showed up on this one, named PSR J2322-2650b, was carbon bound to carbon.<\/p>\n
The planet has roughly the mass of Jupiter, and the much heavier star it hugs has squeezed it into the shape of a lemon. The principal investigator, the University of Chicago\u2019s Michael Zhang, put the deeper problem bluntly in NASA\u2019s announcement of the work<\/a>: the composition \u201cseems to rule out every known formation mechanism.\u201d In other words, the people who found this planet cannot yet say how it came to exist.<\/p>\n A planet you can see because its star is invisible<\/p>\n The star at the center of this system is a millisecond pulsar, the collapsed core of a dead star that spins hundreds of times a second. Zhang described it as having \u201cthe mass of the Sun, but the size of a city.\u201d A pulsar like this one pours out gamma rays and other high-energy particles rather than the visible and infrared light that would normally flood a telescope and drown out a nearby planet.<\/p>\n That quirk is exactly why the planet could be studied at all. Because the pulsar\u2019s glare is invisible to Webb\u2019s infrared instruments, the telescope could track the planet\u2019s own light across its entire orbit without the star washing it out. \u201cThis system is unique because we are able to view the planet illuminated by its host star, but not see the host star at all,\u201d said Maya Beleznay, a Stanford PhD candidate who modeled the planet\u2019s shape and orbit. \u201cSo we get a really pristine spectrum.\u201d<\/p>\n An atmosphere of almost nothing but carbon<\/p>\n What that spectrum showed was, by the team\u2019s own account, a shock. \u201cI remember after we got the data down, our collective reaction was \u2018What the heck is this?’\u201d said co-author Peter Gao of the Carnegie Earth and Planets Laboratory. Instead of the usual water, methane, and carbon dioxide, Webb saw molecular carbon, specifically the forms written as C2 and C3.<\/p>\n That detail carries a lot of weight. Molecular carbon survives as a dominant gas only when there is almost no oxygen or nitrogen around to grab onto, because at these temperatures carbon binds readily to other atoms. The study reports a carbon-to-oxygen ratio above 100 and a carbon-to-nitrogen ratio above 10,000, both far outside the range seen on ordinary worlds. NASA notes that of roughly 150 planets whose atmospheres scientists have examined, inside the solar system and out, no other has shown detectable molecular carbon.<\/p>\n The planet is not a gentle place. NASA puts temperatures from about 1,200 degrees Fahrenheit at the coldest points of the night side to about 3,700 degrees Fahrenheit at the hottest points of the day side, and the study<\/a> reports strong winds blowing westward through that carbon air.<\/p>\n Squeezed into a lemon<\/p>\n PSR J2322-2650b sits extraordinarily close to its star, about 1 million miles away. Earth, by comparison, orbits the Sun at roughly 100 million miles. At that range the planet whips around in a year lasting just 7.8 hours, and the pulsar\u2019s gravity pulls so hard on the near side that the whole world is drawn out of round into a tapered, lemon-like shape.<\/p>\n