A German-led group of astronomers announced on September 20, 2017 that they were recently able to use the Hubble Space Telescope to discover a strange object, a binary asteroid, which are two asteroids orbiting each other and also has comet-like features.
They have been sometimes referred to as rock comets, or active asteroids.
The object has been labeled 2006 VW139/288P. It definitely has comet like features including a bright halo of material called a coma and a long dusty tail.
Astronomers first observed the asteroid pair in September 2016, just before it made it’s closest approach to the sun.
There have been other known comet-asteroid hybrids, like 3200 Phaethon, which spawns the annual Geminid meteor shower.
Asteroid 2006 VW139/288P is the first object to be classified as a binary or double asteroid and also a main-belt comet.