Mars gravity map. Mars Global Surveyor (MGS) image of variations in the gravitational field on the surface of Mars. The degree of variation is colour-coded. Yellow is the mean surface gravity, with orange and red higher and green and blue lower than the mean. Such variations may be caused by the differing densities of rocks in the crust. The data were gathered by studying variations in the path of the MGS spacecraft as it orbited Mars.
Mars gravity map. Photography. Britannica ImageQuest. Encyclopædia Britannica, Inc., 25 May 2016.
http://quest.eb.com/search/132_1296778/1/132_1296778/cite. Accessed 11 Aug 2016.