Normally, astronomers can easily differentiate between comets and asteroids. Comets are comprised of rock and ice and, by approaching the sun at extremely high velocities, ice on their surface sublimates, blasting vapor and dust into space. This is what creates the coma of a comet (an atmosphere like-layer) as well as the tail. On the other hand, asteroids are mostly comprised of rock.
Curiously, in recent years, astronomers discovered that there were some asteroids with comet-like features, which appeared to not only be happily orbiting in the main asteroid belt between Mars and Jupiter, but also exhibited comet-like tails.
“Until about ten years ago, it was pretty obvious what a comet was and what a comet wasn’t, but that is all changing as we realize that not all of these objects show activity all of the time,”
Scott Sheppard, one of the asteroid’s observers said.
Sheppard and Chadwick Trujillo (of the Gemini Observatory) were the ones who discovered the asteroid’s comet-like tail, making 62412 the 13th asteroid of its type in the asteroid belt.
Hygiea asteroids all originate from a massive asteroid 250 mile-wide (once fourth largest asteoid in the belt). The asteroid was fragmented into many smaller asteroids after a huge collision. Why the 62412 asteroid has a tail is still unknown to scientists, however, they believe that ice could have suddenly been exposed to the sun. It then vaporizes and releases dust in the air. Another theory is that there may be asteroid-on-asteroid impacts and that these are causing the comet-like tail.
Astronomers estimate that the main belt contains approximately 100 such objects.