ESA Fly-by Observation of Phobos

This mosaic image is composed by 53 pictures obtained by the Super Resolution Channel (or SRC, a part of the High Resolution Stereo Camera experiment) on board ESA’s Mars Express.

The SRC images covered 70% of the moon's surface. The remaining area is filled with 16 images previously obtained by NASA’s Viking mission. The mean resolution is 12 m/pixel.

Credits: ESA/ DLR (S. Semm, M. Wählisch, K.Willner)/ FU Berlin (G. Neukum)


This image of Phobos’s surface was obtained by the Super Resolution Channel (or SRC, a part of the High Resolution Stereo Camera experiment) on board ESA’s Mars Express on 3 August 2008 (orbit 5889).

The distance from the moon’s centre was 656 km, and the image resolution is 6 m/pixel. The original image has been corrected for mirror distortion.

Mars Express encountered Phobos last night, smoothly skimming past at just 67 km, the closest any manmade object has ever approached Mars’ enigmatic moon.

The data collected could help unlock the origin of not just Phobos but other ‘second generation’ moons.

Phobos Porous
Something is not right about Phobos. It looks like a solid object but previous flybys have shown that it is not dense enough to be solid all the way through. Instead, it must be 25-35% porous.

This has led planetary scientists to believe that it is little more than a ‘rubble pile’ circling Mars. Such a rubble pile would be composed of blocks both large and small resting together, with possibly large spaces between them where they do not fit easily together.

Exquisite Data
Last night’s flyby was close enough to give scientists their most exquisite data yet about the gravitational field of Phobos. Mars Express locked onto the radio signal from Earth at around 21:20 CET (20:20 UT).

The radio frequency oscillators on the ground are 100 000 times more stable than those on the spacecraft, so for this experiment, which required the best precision possible, the signal was sent up to Mars Express and then returned by the spacecraft to the ground.

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