What is the difference between a comet and an asteroid? The typical response is that an asteroid is rocky and a comet is icy/gassy.  Further than this, asteroids typically orbit closer to the Sun than Neptune, and comets orbit beyond this loose dividing line.  But as with everything in nature, there are often exceptions to the rule. C/2014 S3 PANSTAARS is classified as a weakly active comet, originating in the Oort cloud with an orbital period of 860 years.  As it approached the Sun, astronomers noticed that it was lacking the characteristic comet tail, resulting from the blast of solar radiation upon approach to the...