A leading website (universetoday.com) has suggested that asteroids and comets are difficult to distinguish.
Within the category, there is now a question of what is an asteroid and what is a comet. NASA’s flybys of comets and now ESA’s Rosetta at 67P/Churyumov–Gerasimenko are making the delineation between the two types difficult.
A Recipe for Returning Pluto to Full Planethood
The Electric Universe theory (EU theory) has been saying that comets are asteroids. Comets are active asteroids, just on a different orbit (that makes them more active) than most asteroids. That is why they appear to have similar geology features.
More evidence for the Electric Universe theory?