11-20-2017, 02:34 PM
The problem is that it's not clear yet if it's a comet or an asteroid. When first discovered, it was thought to be a comet but recent observations have shown no activity or indications of ice on the surface. However, this doesn't rule out the possibility it's a comet as it's a long way from the sun so may not be active and the colors that suggest it doesn't have ice could be due to the ice being darkened by millions of years of photoprocessing by UV light. It has, though, recently been classified as an asteroid based on those colors, but it's not definite. Things should become a little clearer over the next few months.
ETA: The nature paper was embargoed so didn't have a chance to read it until just now. 'Oumuamua got within 0.25 AU of the sun (a quarter of the Sun-Earth distance - an AU is the average distance between the Sun and the Earth)) and showed no activity. Comets typically show some activity at about 3 AU and sometimes farther away. This seems to be fairly conclusive evidence that 'Oumuamua is an asteroid.
ETA: The nature paper was embargoed so didn't have a chance to read it until just now. 'Oumuamua got within 0.25 AU of the sun (a quarter of the Sun-Earth distance - an AU is the average distance between the Sun and the Earth)) and showed no activity. Comets typically show some activity at about 3 AU and sometimes farther away. This seems to be fairly conclusive evidence that 'Oumuamua is an asteroid.