Astronomers have discovered a new active asteroid with a comet-like tail in our Solar System’s main asteroid belt — a startling find that scientists weren’t expecting.

Designated 62412, the asteroid would be the first comet-like body found in the Hygiea family, according to the Business Standard. The asteroid belt lies between Mars and Jupiter.

While scientists had known about the asteroid for a while, they thought it was just a standard asteroid, until they noticed a tail at the end of it. This indicates it is what is known as an “active” asteroid — the 13th one found in the main asteroid belt. It leads researchers to believe that there are about 100 of them total in the belt.

Scientists don’t yet know why asteroids lose material and develop a tail, but they suspect that recent impacts or the transformation of exposed ice from solid to gas could help explain it.

Scientists used to believe that asteroids were unchanging, but with improved technology comes improved methods of observing them, allowing for the discovery of tails and a thin “atmosphere” around the comet known as a coma.

The newly discovered active asteroid has a very fast rotation, according to researchers, with material shifting on its surface and making up its tail to make it look like a comet. They don’t know if the tail is from material thrown off the main rock, or from ice being turned into vapor.

The Solar System’s asteroid belt is filled with irregularly shaped rocks from the creation of the universe, and about half of its mass comes from the four largest asteroids, Hygiea, Pallas, Veres, and Vesta. Ceres, the largest of the four, is considered a dwarf planet due to its size (590 miles in diameter).

The new comet-like asteroid was found in the vicinity of Hygiea, the fourth largest asteroid. It is estimated to be in the area of between 350 and 500 kilometers (the difference is due to its oblong shape) and it has 2.9 percent of the mass of the belt. It has a dark surface that makes it difficult to be viewed from Earth. Because of that, it wasn’t discovered until 1849.