Astronomers think some asteroids have been comets all along. Heres why.

For nearly three decades, astronomers tracked a 1,250-foot-wide object relatively close to Earth that they thought was an asteroid. It looked like one. It followed the expected path. Telescopes saw no glowing cloud of gas or dust tail sweeping behind it. Then, the space rock, called 1998 SH2, drifted from its usual orbit that gravity alone predicted. Something was giving it a tiny push. Astronomers eventually realized that the culprit was likely gas escaping from its surface — a