Europe's Mars Express spacecraft has returned some remarkable close-up images of the Red Planet's Phobos moon.
The probe passed just 93km from the rock on 23 July, allowing its High Resolution Stereo Camera to take extremely detailed pictures.
Potato-shaped Phobos is 27km in its longest dimension and is thought to be a captured-asteroid or a remnant of the material that formed the planets.
The new images include portions of the moon not previously photographed.
They also show clearly the satellite's famous grooves.
How these were generated is not entirely understood. Some scientists believe they have been gouged out by material thrown up from the surface of Mars by space impacts.
Other researchers think they could have resulted from the surface regolith, or soil, slipping into internal fissures.
The images are sure to provide new insights. At their best, the pictures have a resolution of 3.7m per pixel.
PHOBOS - MARTIAN MOON
Measures 27 x 22 x 18km; could be a captured asteroid
Orbits less than 6,000km above Mars; slowly falling inwards
First high-res probe images taken by Mariner 9 in 1971
Dedicated Soviet probes, Phobos 1 & 2, were lost
Its 10km-wide Stickney crater records huge impact
They will also assist the Russians in their planning of the Phobos-Grunt mission. Launching next year, this venture will try to place a spacecraft on the moon to gather samples for return to Earth.
Phobos was discovered in 1877 by the American astronomer Asaph Hall.
Its orbit around Mars is dropping by about 1.8m (5.9ft) every 100 years. This means that in 50 million years it will either crash into Mars or break up into a ring.
Mars Express is operated by the European Space Agency.
Nasa's Mars Reconaissance Orbiter (MRO) took pictures of Phobos earlier this year from a distance of several thousand km.