Mars Express has Phobos

in sight
BY DR EMILY BALDWIN
ASTRONOMY NOW

Posted: July 18, 2008

Scientists and engineers are preparing ESA's Mars Express for several close fly-bys of the Martian moon Phobos, in the quest to settle debate on the origin of the red planet’s two rocky satellites.

Phobos, the larger and innermost of the two Martian moons, is seen here floating above the red planet by the HRSC camera onboard Mars Express. Image: ESA/ DLR/ FU Berlin (G. Neukum).

Over the last week Mars Express has been conducting a number of flybys of the tiny moon at progressively closer distances, in preparation for its nearest glimpse from a distance of just 97 kilometres, scheduled for 23 July. At just a stone’s throw away, Mars Express will conduct some of the most detailed investigations of the moon to date.

Thanks to the fleet of Martian orbiters and surface landers and rovers, Mars itself has been studied in great detail, but very little is known about the origins of its moons, Phobos and Deimos. Several theories have been aired, but it is unclear if the moons are asteroids captured by the red planet’s gravity, surviving planetesimals – building blocks – of the very early Solar System, or remnants of a massive impact of a large object on Mars that were thrown into orbit around the planet.

As Mars Express closes in on Phobos, spacecraft operations will be set to optimise the maximum return of science results, and the data gathered will help scientists answer these long-standing questions. Previously unseen areas of the tiny moon will finally be photographed by the High-Resolution Stereo Camera (HRSC), which will also document the moon's surface in colour and in three dimensions. These three-dimensional ‘stereo’ images of the moon’s topography will enable a digital terrain model (DTM) to be constructed, which, like virtual reality, will allow scientists to visualise what it would be like to stand on the surface of Phobos.

A high resolution view of the Mars-facing side of Phobos. At closest approach of 97 kilometres next week, even finer detail will be resolved, along with previously unseen regions of the moon. Image: ESA/DLR/FU Berlin (G. Neukum).

The Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS) will collect information during two flybys in late July on the topography of the moon's surface and on the structure of its interior, while the Visible and Infrared Mineralogical Mapping Spectrometer (OMEGA), the Planetary Fourier Spectrometer (PFS) and the Ultraviolet and Infrared Atmospheric Spectrometer (SPICAM), will gather details on the surface composition, geochemistry and temperature of Phobos. The Energetic neutral atoms analyser (ASPERA) will study the environment around Phobos, in particular the plasma that surrounds the moon and also the interaction of the moon with the solar wind.

Mars Express may also attempt to image a possible landing site identified for Russia's planned sample return ‘Phobos-Grunt’ mission, currently due for launch in 2009, which will collect samples of the moon’s surface and return them to Earth for scientific research.