"This flyby will provide very good viewing, within 1,000 km (620 miles), of an area previously not seen well," said ESA's Mars Express project scientist Dmitri Titov. "HRSC will be taking images; the MARSIS radar and the ASPERA-3 particle instrument will operate as well to sound the subsurface and plasma environment of the moon."
Within the flyby region is the proposed landing site for the future Russian lander and sample-return mission, Phobos Grunt. The mission was first launched in 2011, but failed when the spacecraft became stranded in low-Earth orbit and ultimately reentered the atmosphere. It is hoped that a repeat attempt may happen by 2026.
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"This flyby is important as it will allow us to finally view this area on Phobos that has yet to be seen at high resolution and excellent lighting," said Thomas Duxbury, professor in planetary science at George Mason University, Va.
In addition, the incredibly close encounter will cause Phobos' weak gravitational field to slightly alter Mars Express' orbital trajectory. In 2013, another close flyby (passing within 45 km or 28 miles) allowed scientists to detect the gravitational deflection so a precise measurement of Phobos' mass and average density could be arrived at. Thursday's flyby will be used to confirm and tightly refine these measurements.