PacSci Doku

Here's a twist on Sudoku, named after the institution where I work. A new PacSci Doku comes out every other week here. I use letters instead of filling the blanks with numbers. Hidden in one of the columns or rows is the answer to a science question. I then provide some information about the answer on the solution page for the PacSci-Doku. Here is one of my favorite examples:

What is the source of the meteors in a meteor shower?

U O E N K C T G M

Each row and column in the grid below has to have only one of each of these letters. Each of the 3 x 3 mini-squares in the 9 x 9 square also needs to have only one of each letter.

Click here for the solution