Comet Lulin

Apparently some proponents of the 2012 doomsday are pointing to comet Lulin (C/2007 N3) as 'proof' that there will be a global disaster in 2012. Lulin is a non-periodic comet that was first discovered in July of 2007, and it was the third comet discovered in that period. See the comet names page for more information.

Unusual Properties

It was an exciting object for a few reasons.

This was likely the first and only pass that the comet will ever make. Its path was parabolic, which means that it is not likely to be recaptured by the sun's gravity.

The orbit was retrograde. That is not unheard of, just unusual. There are numerous retrograde objects in the solar system, including many moons of the gas giants.

The green color is related to the fact that this was the first pass. The unusual color comes from the more volatile compounds in the comet nucleus. These tend to boil off quickly, so the first pass of a comet by a sun will cause these compounds to be depleted. After just a few passes (in the case of a periodic comet) the unusual colors are gone¹.

Because of the retrograde orbit and the low angle of inclination, the comet was a fast mover. In fact you could watch it move against the background of stars visually.

Proof of what?

I'm not sure what the comet is supposed to prove. We get so-called 'rogue' (meaning non-periodic) comets all of the time.

Unusual is not the same as unheard-of

Since we put up the SOHO and STEREO spacecraft we've learned that a lot of small comets fall in and burn up in the sun's atmosphere.

The green color and retrograde low-angle orbit are all unusual, but not unheard of. There have been many comets that were more spectacular in history².

Charles Messier carefully observed and documented 44 of comets back in the 1700s and 1800s.

Interesting but not spectacular

Lulin was at best a binocular object, and you really needed a 6-inch or better telescope to get a good look at the color. The excitement over Lulin was the unusual features (young, retrograde, green, fast) and not the visual sight³.

Conclusion

Throughout history comets were viewed with superstition and fear, hailed as omens of evil. With the advent of rationality and science we know that these objects are not omens of doom, but rather interesting celestial objects. Comet Lulin's properties were unusual, but not unique, and its appearance in our skies does not prove impending doom.