Mars Express closed in on the intriguing martian moon Phobos at 6:49 CEST on July 23rd, flying past at 3 km/s, a mere 93 km from the moon. The European Space Agency's (ESA) spacecraft's fly-bys of the moon have returned its most detailed full-disc images ever, also in 3-D, using the High Resolution Stereo Camera (HRSC) on board. Phobos is what scientists call a 'small irregular body'. Measuring 27x22x19 km, it is one of the least reflective objects in the Solar System. It is believed Phobos is a capture-asteroid or a remnant of the material that formed the planets. The HRSC images, which are still under processing, form a bounty for scientists studying Phobos. They are a result of observations carried out over several close fly-bys of the martian moon, performed over the past three weeks. At their best, the pictures have a resolution of 3.7 m/pixel and are taken in five channels (in the stereo channel) for images in 3-D and (in the photometric channels) to perform analyses of the physical properties of the surface. This is the first time portions of the far-side of the moon have been imaged in such high resolution (Phobos always faces Mars on the same side).

In observing Phobos, Mars Express benefits from its highly elliptical orbit, which takes it from a closest distance of 270 km from the planet to a maximum of 10,000 km (from the center of Mars), crossing the 9,000 km orbit of the Martian moon. Mars Express imaged the far-side of Phobos (with respect to Mars) for the first time after NASA's Viking mission, by flying outside the spacecraft's orbit around Mars. Phobos-Grunt (Phobos soil), a Russian sample-return mission, is due to launch in 2009. This region was last imaged in the 1970s by the Viking orbiters.