your question is not as simple as you think it is because of the tremendous amount of disinformation surrounding this issue. "comet elenin" is not a comet at all. it is a spaceship and nasa has admitted that it is under intelligent control. also that it has moved in ways that no comet does. elenin apparently travels with nibiru, also called planet x, tyche, the destroyer and eris. the nature of this celestial body is a matter of disagreement. it is believed to be a brown dwarf, or failed star, by some, it is by all accounts, hard to see unless you are close to it or using an infrared telescope. however, it is believed to be between 14 and 20 times the size of earth, and it has seven moons that rotate around it.

I have read that nibiru has an elliptical orbit and passes through our solar system and quite close to earth every 3600 years, wreaking havoc on its way.

I hope this helps and for further info you can go to elenin.org, or google terral03.