Strange Helmet on Mars - Spirit Rover Image!!

Mars has many strange things. This is one of them. It resembles Alien's helmet or skull. NASA's Spirit Rover has taken this Photo.
Image Source - Spirit Rover Sol 2114 ( http://mars.nasa.gov/mer/gallery/all/spirit_p2114.html )  http://areo.info/mer/spirit/2114/tn/2P314033514EFFB270P2556L5M1_L2L5L5L7L7.jpg.html