US Naval Research Laboratory scientist Dr. Karl Battams has recently tweeted
Unlike 'Oumuamua, whose asteroid-or-comet nature still gets debated, this one is definitely a comet. If it is unequivocally interstellar, it'll be fascinating to see how its composition (spectral properties) compare to the variety we see in comets from our own solar system.
Answers to Do astronomers generally agree that the distinction between comets and astroids is not so clear? suggest that the distinction can be a hard call sometimes, and some might instead call small solar system bodies formerly known as
Prince comets and asteroids just that; SSSBs.
Question: What might cause astronomers like Dr. Battams be so confident that this object is a comet and not an asteroid, besides the fact that it's being called one? (Comet C/2019 Q4 (Borisov))
Is it just the orbit itself, or are there other observational data such as brightness in the infrared?