麻豆传媒

Mars鈥檚 little potato-shaped moon Phobos takes centre stage in stunning new false-colour and 3D images snapped by NASA鈥檚 Mars Reconnaissance Orbiter. The moon, which some say would make an ideal destination for human space exploration, will one day be destroyed by the Red Planet.

In 2009, Russia is launching a robot meant to return a sample of the 22-kilometre-wide moon to Earth. Some scientists have also suggested that astronauts should head to the tiny moon, which might be a captured asteroid.

That鈥檚 because its gravity is less than 1/1000^th the strength of that on Earth, making it relatively easy to land on and leave again. Meteorite impacts may also have blasted samples of Martian rock up to its surface, where astronauts could easily retrieve them.

Any base set up there would have a finite lifetime, however, since Phobos is spiralling towards Mars at a rate of 1.8 metres per century. It faces a grim fate 鈥� it will eventually either smash into Mars or get ripped apart by the planet鈥檚 gravity, although scientists estimate this will not occur for another 50 million years or so.

But for now, the moon is enjoying a close-up look by NASA鈥檚 Mars Reconnaissance Orbiter (MRO), which carries the most powerful camera ever sent to another planet. On 23 March, the camera, called HiRISE (High Resolution Imaging Science Experiment), took some detailed new images of Phobos from 6800 and 5800 kilometres away.

Giant crater

Phobos appears in false colour in the new images, which were made by combining snapshots taken at three different wavelengths of visible and infrared light.

Phobos鈥檚 surface is dominated by a large crater called Stickney. It stretches across 9 kilometres, or about 40% of Phobos鈥檚 diameter. The impact that produced it is thought to have come close to shattering the moon to pieces.

Material around Stickney鈥檚 rim is bluer 鈥� and therefore younger 鈥� than elsewhere on the moon鈥檚 surface. 鈥淏ased on analogy with material on our own Moon, the bluer colour could mean that the material is fresher, or hasn鈥檛 been exposed to space as long as the rest of Phobos鈥檚 surface has,鈥� says HiRISE team member Nathan Bridges of NASA鈥檚 Jet Propulsion Laboratory in Pasadena, California, US.

Streaks visible on the walls of Stickney and other craters are thought to be places where material has tumbled down slopes in landslides.

Strafed surface

And Phobos bears other scars of past violence. Much of its surface is riven by troughs and pockmarked by chains of craters. These may be places where the moon鈥檚 surface was strafed by shrapnel thrown out by meteorite impacts on Mars.

In the closer of the HiRISE images, each pixel is about 5.8 metres across. Although other spacecraft such as NASA鈥檚 Mars Global Surveyor, which is now lost, have passed closer to the moon and returned images with higher resolution, the HiRISE pictures are of better quality because the data they were made from contain less 鈥榥oise鈥�.

Scientists have also combined HiRISE images taken from slightly different angles to produce a 3D view of the moon 鈥� something that has been previously done using images from the European Space Agency鈥檚 Mars Express spacecraft.

are available from NASA.

Mars 鈥� The Red Planet is full of surprises; learn more in our continually updated .