Researchers using the Hubble Space Telescope have discovered something strange lingering near the asteroid belt separating Mars and Jupiter. No, it’s not Nibiru, a mythical planet that many claimed would crash into Earth this past weekend (it didn't). The strange object was a pair of asteroids, collectively known as 288P that are behaving in a way astronomers have never observed before, reports Calla Cofield at Space.com.

Binary asteroids are a pair of space rocks that orbit one another—and they're are not uncommon, Cofield reports. Also not unusual are asteroids that spurt vapor into space, creating a long tail like a comet. But 288P combines these two features: It's the first binary asteroid system that also vents into space ever found, making it the first object classified as both a binary asteroid and a comet. The researchers detail the find in the journal Nature.

As Elizabeth Howell at Seeker reports, 288P was discovered in November 2006 and, at the time, it was classified as an asteroid. But in 2011, researchers noticed its comet-like tail. At the time, observations hinted that 288P could actually be the result of two objects. And in September 2016, when Hubble peered out at the pair of space rocks, these suspicions were confirmed.

The two asteroids are each about two-thirds of a mile wide and are orbiting one another at a distance of roughly 62 miles, which Cofield reports is ten times further apart than asteroids of their size usually orbit one another. They also have an eccentric orbit compared to other objects in the asteroid belt.

Lead author of the paper Jessica Agarwal says it’s likely 288P has only been a binary system for about 5,000 years, created when a larger asteroid broke into pieces. “The most probable formation scenario of 288P is a breakup due to fast rotation,” she says in a press release. "After that, the two fragments may have been moved further apart by sublimation torques.”

As Howell reports, in the asteroid belt, ice can exist for billions of years if it is covered by a thick layer of dust, blocking the sun’s radiation. It’s likely that dust layer has eroded off 288P and that the tail is created by the asteroid-comet shedding water vapor as it orbits closer to the sun.

It’s possible that ejection of water vapor might affect the orbit of the binary system, over time pushing it into its unusual orbit, Agarwal tells Cofield. “If that is the case, it basically can change our understanding of how asteroids evolve, so how fast they disintegrate and change their sizes,” Agarwal says. “And this in turn can also change our understanding of how they have evolved in the past … [and] our models of the initial distribution of asteroids in the asteroid belt.”

While researchers know there are vapor-spewing asteroids in the asteroid belt, Agarwhal says we don’t know how much water they harbor—or how much was present at the beginning of the solar system and how it impacted planetary development.

But as researchers continue their forays into the great beyond, they are gathering more and more clues. In 2011 and 2012, NASA’s Dawn explorer investigated the protoplanet Vesta, one of the largest objects in the asteroid belt. The craft is currently exploring another massive object in the belt: dwarf planet Ceres, which may contain massive amounts of water.