The pin is made by AB Emblems the NASA Contractor for mission emblems. It is approximately 1 inch in diameter.

When purchasing mission lapel pins be sure to check the embossing on the back of the pin:

NASA
STS-107
ABEmblem.com

to make sure you are getting the NASA authorized pin from AB Emblems.

This is the emblem of he fatal last mission of Space Shuttle Columbia. The orbiter and crew were lost during re-entry.