Observations by the first infrared space telescope saw something weird beyond Uranus.
In 1983, astronomer Michael Rowan-Robinson conducted a search for a proposed 10th planet (Pluto still being a planet at the time) using data from the Infrared Astronomical Satellite, the first infrared space telescope. Rowan-Robinson didn’t turn up a new planet, and by 1991, he was pretty sure that such a planet did not exist, at least not in the area of the sky he looked in.
But since then, new regions of the sky have been proposed as potential homes of a hidden planet, now called Planet Nine. Some astrophysicists suspect that a planet—or at least, something with a lot of gravity—exists out there due to the movements of objects in the Kuiper Belt, a distant disc of comets, asteroids, and icy things beyond the orbit of Neptune.
On the heels of recent research that suggested new potential hiding spots for Planet Nine, Rowan-Robinson revisited the 38-year-old data and found three infrared sources that he says could be the theorized world. His paper is set to be published in the Monthly Notices of the Royal Astronomical Society and is currently hosted on the preprint server arXiv.
Planet Nine (formerly Planet X, said like the letter) has long been considered a possibility. The discovery of Neptune in 1846 came after astronomers found Uranus’s orbit was slightly different than math predicted. They realized that something was perturbing Uranus gravitationally; that object turned out to be an eighth planet.
Observations of Neptune then led astronomers to believe there may be yet another planet out there, messing with the newly discovered world’s orbit. Pluto was found in 1930 by looking at objects on photographic plates, but it couldn’t account for the movement of Neptune.
Scientists who search for Planet Nine estimate that its mass is several times bigger than Earth’s, with an orbit lasting thousands of years. Of course, Planet Nine is just one answer to the quandary of why some objects’ orbits are wonky. One alternative theory is that instead of Planet Nine is actually a ring of debris. Others have suggested the “planet” could be a bowling ball-sized black hole.