This project began two years ago when we asked several several scientists from various fields what they thought were the greatest mysteries. From their input, we wrote about 14 big enigmas. None have been solved since. So last month, we asked you to rank the list. What follows, backed by more than 8,000 of your votes as of May 7, 2009, are 10 of the greatest mysteries facing science today. No. 1 was, as we had figured it might be, a clear winner with 20 percent of the vote (No. 2 got 16 percent)