During Mars Express’ fly-bys of Phobos, the MaRS radio science experiment on Mars Express detected the gravitational influence of the moon on the trajectory of the spacecraft, so allowing the determination of the moon’s mass with unprecedented accuracy (1.072 1016 kg, or about one billionth the mass of the Earth). The 3D model of the body built thanks to HRSC data, combined with the mass measurement, is key to calculate the mean density of Phobos. In turn, this can tell scientists a lot about the moon’s composition (how much rock or ice may be present, and how porous the structure may be), helping to close in on Phobos’ origin.

Credits: ESA/ DLR (K.Willner)/ FU Berlin (G. Neukum)

The Camera Head is the light grey unit in the middle and the top rectangular aperture. The Super Resolution Channel (SRC) is the black cylindrical aperture at lower right. The Camera Head and SRC together measure 515 x 300 x 260 mm. The Digital Unit is the black box at the back. The complete HRSC weighs 20.4 kilograms and consumes about 48.7 Watts with both camera and SRC working.

Credits: DLR/FU Berlin/ESA 2003