Images have been released following the Mars Express spacecraft’s flyby of Phobos on March 7, 2010, showing Mars’ rocky moon in exquisite detail, with a resolution of just 4.4 metres per pixel. They also show the proposed landing sites for a forthcoming Russian robotic sample-return mission.
The European Space Agency’s (ESA) Mars Express orbits the Red Planet in a highly elliptical, polar orbit that brings it close to Phobos every five months. It is the only spacecraft currently in orbit around Mars whose orbit reaches far enough from the planet to provide a close-up view of Phobos.
Like our Moon, Phobos always keeps the same side facing the planet, so it is only by flying outside the moon’s orbit that it becomes possible to observe the far side. Mars Express did just this on March 7, 10 and 13. The spacecraft also collected data with other instruments.
Phobos is an irregular body measuring some 27 x 22 x 19 kilometres. Its origin is debated. It appears to share many characteristics with the class of ‘carbonaceous C-type’ asteroids, which suggests it might have been captured as it wandered past. However, it is difficult to explain either the capture mechanism or the subsequent evolution of the orbit into the equatorial plane of Mars. An alternative hypothesis is that it formed around Mars, and is therefore a remnant from the planetary formation period.
This Mars Express image shows the proposed landing sites for the Russian Phobos-Grunt mission, due for launch next year. Phobos-Grunt will scoop up samples of Phobos’ surface and return them to Earth.
In 2011 Russia will send a mission called Phobos-Grunt (meaning Phobos Soil) to land on the Martian moon, collect a sample and return it to Earth for analysis.
For operational and landing safety reasons, the proposed landing sites were selected on the far side of Phobos. This region was imaged by Mars Express’ high-resolution camera (HRSC) during the July-August 2008 flybys of Phobos. But new HRSC images showing the vicinity of the landing area under different conditions, such as better illumination from the Sun, remain highly valuable for mission planners.
It is expected that Earth-based ESA stations will take part in controlling Phobos-Grunt, receiving telemetry and making trajectory measurements.
Mars Express will continue to encounter Phobos until the end of March, when the moon will pass out of range. During the remaining flybys, HRSC and other instruments will continue to collect data.
Adapted from information issued by ESA / DLR / FU Berlin (G. Neukum).
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