A strangely persistent patch of frozen water is among the features imaged by NASA's Mars Reconnaissance Orbiter (MRO) in the first few days since it started its main phase of science observations. It also spotted gouges from landslides that have left no visible debris behind.

MRO arrived at Mars in March 2006, but spent its first few months skimming in and out of the Martian atmosphere to tighten its orbit around the Red Planet.

It then underwent a period of instrument testing, followed by a hiatus beginning in mid-October when the Sun was too close to Mars, as seen from Earth, for reliable radio communication. This prevented MRO from beginning its primary science phase until 7 November.

Now, some first images have been released, taken with MRO's High Resolution Imaging Science Experiment (HiRISE), the most powerful camera ever sent to Mars.

One image (right) shows gullies carved in the sides of sand dunes in the Russell Crater. These gullies were first imaged by Mars Global Surveyor (MGS) and are puzzling because they do not have deposits of debris at their ends, as do other gullies seen on Mars, thought to be due to avalanches.

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DA Morgan