NEOWISE has found that Hartley leaves a 'bumpy' trail as it orbits the sun, dotting the celestial landscape with grains as big as golf balls. "We were surprised that carbon dioxide plays a significant role in comet Hartley 2's activity when it's farther away from the sun," said James Bauer, the lead author of a new paper on the result in the Astrophysical Journal.
So, it turns out to be that the comet emits carbon dioxide, still orbiting at 2.3 AU from the sun. An astronomical unit (AU) is a common measurement used in relatively close objects (like asteroids and comets). It is the 93 million miles, or the distance between the earth and sun. Hopefully, as Comet Hartley 2 continues orbiting, NEOWISE will be able to obtain more information about its "irregular" tail.
|Here, you can distinguish the tail, but not the particles.|