Comets And Asteroids

Comets and asteroids are typically represented as different classes of objects. Asteroids are rocky bodies that basically orbit the Sun inside the orbit of Jupiter. Comets, on the other hand, contain volatiles, gas and ice, and spend most of their time in the far reaches of the Solar System, swooping in close to the Sun only occasionally.

Then we have 596 Schelia. Discovered in 1906 and classified as an asteroid because it orbits in the Main Belt of asteroids between Mars and Jupiter, new observations of Schelia suggests it might have a coma and a wispy tail-- characteristics of comets. Schelia thus seems to be the latest in a small group of bodies that seem to straddle the line between asteroids and comets. Astronomers are perplexed by Schelia, for example, because a body orbiting in the Main Belt shouldn't have been able to retain volatiles from the beginning of the Solar System. One obvious solution, of course, is that Schelia has not always orbited where it does now.

On a broader perspective, perhaps comets and asteroids are in fact fundamentally the same thing. A rocky body orbiting too close to the Sun to hold on to ice is an asteroid, but put that same body out beyond Neptune where it could retain ice, and maybe it's a comet. Schelia might be making that case.