Comets explained: the icy visitors

What BBN said about it

1. 

   Hank Ledger · Lead AnchorThe claim under review: comets are dirty snowballs left over from the birth of the solar system about four point six billion years ago.

2. 

   Hank Ledger · Lead AnchorNASA's reference page says that is about right.

3. 

   Vera Bullock · Co-AnchorFour point six billion years of leftovers, and nobody in the universe has taken out the trash.

4. 

   Vera Bullock · Co-AnchorI find that very healing, and also a little rude.

5. 

   Hank Ledger · Lead AnchorSome come back in under two hundred years.

6. 

   Hank Ledger · Lead AnchorThe ones from the Oort Cloud can take thirty million years to finish one trip around the Sun.

7. 

   Vera Bullock · Co-AnchorThirty million years?

8. 

   Hank Ledger · Lead AnchorYes. And each comet has two tails, one of dust and one of gas.

9. 

   Vera Bullock · Co-AnchorSo it shows up unannounced, trails its own mess in two directions, and then makes you wait thirty million years for an apology.

10. 

    Vera Bullock · Co-AnchorFull Bonkers.

11. 

    Hank Ledger · Lead AnchorNASA says comets may also have brought Earth its water. So the rating is Full Bonkers, and you've been drinking the leftovers.