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Mars Express close flybys of martian moon Phobos

Copyright ESA

Mars Express has returned images from the Phobos flyby of 9 January 2011. Mars Express passed Mars’ largest moon at a distance of 100km.

Phobos Flyby Success

Phobos Flyby Success

Copyright ESA

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.

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.

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 [...]

ESA closes in on the origin of Mars larger moon

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Copyright ESA

European space scientists are getting closer to unravelling the origin of Mars’ larger moon, Phobos. Thanks to a series of close encounters by ESA’s Mars Express spacecraft, the moon looks almost certain to be a ‘rubble pile’, rather than a single solid object. However, mysteries remain about where the rubble came from.

Unlike Earth, with its single large moon, Mars plays host to two small moons. The larger one is Phobos, an irregularly sized lump of space rock measuring just 27 km x 22 km x 19 km.

During the Summer, Mars Express made a series of close passes to Phobos. It captured images at almost all fly-bys with the High Resolution Stereo Camera (HRSC). A team led by Gerhard Neukum, Freie Universität Berlin, also involving scientists from the German Aerospace Centre (DLR), is now using these and previously collected data to construct a more accurate 3D model of Phobos, so that its volume can be determined with more precision.

In addition, during one of the nearest fly-bys, the Mars Express Radio Science (MaRS) Experiment team led by Martin Pätzold, Rheinisches Institut fuer Umweltforschung at the University of Cologne, carefully monitored the spacecraft’s radio signals. They recorded the [...]

Mars Express acquires sharpest images of martian moon Phobos

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Copyright ESA

Mars Express closed in on the intriguing martian moon Phobos at 6:50 CEST on 23 July, flying past at 2.96 km/s, only 100 km from the centre of the moon. The 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 on board.

Phobos is what scientists call a ‘small irregular body’. Measuring 27 km × 22 km × 19 km, it is one of the least reflective objects in the Solar System, thought to be a captured 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 to obtain images in 3-D and to perform analyses of the physical properties of the surface.

The images obtained by several other spacecraft so far have either been of a lower resolution, or not available in 3D and have not covered the [...]