Unique Thing on Mars..!!

This unique thing appears in below Nasa Image...

In above image... everything is in same colour except in the Circle in the center. That shines more. So that attracts me. Location of this Nasa image is http://apod.nasa.gov/apod/image/1103/marsapan_phoenix_13070.jpg

Download Nasa Image... then zoom in that... find out this thing. This is Mars Panorama from the Phonix Lander. Nasa Published this Image on 13-Mar-2011. Did not say anything about this thing.