Missing Piece

Phoenix, which is a lander working on Mars, apparently found the key substance.

Phoenix found perchlorate. According to the web site, this substance can be a clue to the method to search life on Mars, and it might have been in the soil which Viking Mars lander caught.
Viking Mars lander might also have found it, but this lander could not prove the existence.
So, they call this discovery the missing piece.

It looks interesting.

Here is the picture of Phoenix for NASA site.