Most detailed pictures ever of Phobos taken by Mars Express / Sonda europea envía imágenes únicas de luna Phobos en Marte

Thursday, July 31, 2008

Those of us over on's forums have been looking forward to this flyby for quite some time. Mars Express had its closest flyby yet of Mars' larger moon, Phobos, flying within 100 km and sending back some remarkably detailed images. Here's the link to ESA's page on the flyby.

First of all, to see how the flyby worked, take a look at this .gif animation.

Phobos is under 10,000 km away from the surface of Mars, which is about 35 times closer than our Moon, though it's much smaller of course. Wikipedia has some information on Mars looks like from Phobos and vice versa:

As seen from Phobos, Mars would appear 6,400 times larger and 2,500 times brighter than the full Moon appears from Earth, taking up a quarter of the width of a celestial hemisphere.

Phobos orbits Mars below the synchronous orbit radius, meaning that it moves around Mars faster than Mars itself rotates. Therefore it rises in the west, moves comparatively rapidly across the sky (in 4 h 15 min or less) and sets in the east, approximately twice a day (every 11 h 6 min). Since it is close to the surface and in an equatorial orbit, it cannot be seen above the horizon from latitudes greater than 70.4°.

As seen from Mars' equator, Phobos would be one-third the angular diameter of the full Moon as seen from Earth. Observers at higher Martian latitudes would see a smaller angular diameter because they would be significantly further away from Phobos. Phobos' apparent size would actually vary by up to 45% as it passed overhead, due to its proximity to Mars' surface: for an equatorial observer, for example, Phobos would be about 0.14° upon rising and swell to 0.20° by the time it reaches the zenith. By comparison, the Sun would have an apparent size of about 0.35° in the Martian sky.

Okay, now for one of the pictures:

Soon we'll also be able to see the surface of the moon and obtain samples from its surface:
Scientific bounty

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 centre of Mars), crossing the 6000 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 in the 1970s, by flying outside the spacecraft’s orbit around Mars.

Phobos-Grunt (roughly translated as Phobos soil), a Russian sample-return mission, is due for launch in 2009. It is expected to land on the far-side of Phobos at a region between 5° south to 5° north, and 230° west to 235° west.


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