This special position of Mars and its traditional character is also manifested by its size, the degree of internal activity, the age of its surface features, and the density of its atmosphere. These properties are intermediate between those of the large terrestrial planets (Earth, Venus) and the smaller planetary bodies (Mercury, the Moon, the asteroids). Exploration of Mars is crucial for a better understanding of the Earth from the perspective of comparative planetology.

The scientific objectives of the Mars Express mission represent an attempt to fulfill part of the lost scientific goals of the ill-fated Russian Mars-96 mission.

• Global high-resolution photogeology (including topography, morphology, paleoclimatology, etc...) at 10 m resolution
• Super-resolution photogeology of selected areas of the planet (2 m/pixel)
• Global high spatial resolution mineralogical mapping of the Martian surface at kilometer scale down to several 100 m resolution
• Global atmospheric circulation characterisation, and high-resolution mapping of the atmospheric composition
• Subsurface structure characterisation at kilometer scale down to the permafrost
• Surface-atmosphere interaction; interaction of the atmosphere with the interplanetary medium
• Structure of the interior, atmosphere and environment via radio science measurements
• Surface geochemistry and exobiology