Europe's Mars Express spacecraft has taken its most detailed image yet of the Red Planet's largest moon, Phobos.
The photo was taken from a distance of about 200km (124 miles) from the irregular-shaped satellite and shows the side of the object that faces Mars.
Scientists hope to explain the origin of a network of grooves that extend from the equator to the north pole.
Phobos is slowly falling down to Mars and is expected to crash into the planet in the next few million years.
Measuring about 27km by 19km, Phobos (from the Greek for fear) is the larger of two moons in orbit around Mars.
Its smaller companion, Deimos, is about half Phobos' size and orbits Mars more distantly.
Phobos is locked in a so-called "death spiral", which means it is in an orbit that is gradually pulling it on a collision course with the surface of the planet.
It orbits Mars three times a day, and is so close to the planet's surface that in some locations it can never be seen.
There are competing theories of Phobos' origin. One theory proposes that the satellite is a captured asteroid. The moon appears to be composed of C-type rock, similar to blackish carbonaceous chondrite asteroids.
But some scientists say there is evidence that Phobos and Deimos are by-products of the break-up of a huge moon that once circled Mars.
The Mars Express image has a resolution of about seven metres per pixel.