* Astronomy

These images, taken by the High Resolution Stereo Camera (HRSC) aboard ESA’s Mars Express spacecraft, show a large depression called Iani Chaos and the upper reaches of a large outflow channel called Ares Vallis.
Image strips were taken in October 2004, during three orbits from a 350-kilometre altitude, with a resolution of 15 metres per pixel. The strips have then been matched to a mosaic that covers an area from 17.5º western longitude to 3º North.
The Iani Chaos depression – 180 kilometres long and 200 kilometres wide – is connected to the beginning of Ares Vallis by a 100-kilometre wide transition zone.
Ares Vallis continues its course for about 1400 kilometres through the ancient Xanthe Terra highlands, bordered by valley flanks up to 2000 metres high. Eventually Ares Vallis empties into Chryse Planitia.


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These images help illuminate the complex geological history of Mars. Ares Vallis is one of several big outflow channels on Mars in this region that formed billions of years ago. Many surface features suggest that erosion of large water flows had carved Ares Vallis in the Martian landscape.
Most likely gigantic floods ran downhill, carving a deep canyon into Xanthe Terra. Rocks eroded from the valley flanks were milled into smaller fractions and transported in the running water.

Finally this sedimentary load was deposited far north at the mouth of Ares Vallis in the Chryse plains, where NASA’s Mars Pathfinder landed in 1997 to search for traces of water with its small Sojourner rover.

The scenes displayed in the images show the transition zone between Iani Chaos and Ares Vallis. A chaotic distribution of individual blocks of rock and hills forms a disrupted pattern. These ‘knobs’ are several hundred metres high. Scientists suggest that they are remnants of a pre-existing landscape that collapsed after cavities had formed beneath the surface.

The elongated curvature of features extending from south to north along with terraces, streamlined 'islands' and the smooth, flat surface in the valley centre are strong hints that it was running water that carved the valley.

Ice stored in possible cavities in the Martian highland might have been melted by volcanic heat. Pouring out, the melting water would have followed the pre-existing topography to the northern lowlands.
A hundred kilometres further, a ten-kilometre-wide valley arm merges into Ares Vallis from the west. Large amounts of water originating from Aram Chaos (outside the image) joined the stream of Ares Vallis. Fan-shaped deposits on the valley floor are the remnants of landslides at the northern flanks.

At the freshly eroded cliffs possible lava layers are visible: such layers are found almost everywhere in Xanthe Terra. Further downstream, another valley branch enters Ares Vallis from the east after passing through an eroded impact crater in Xanthe Terra. West of Ares Vallis, a subtler riverbed is running parallel to the main valley.


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Windows Media movie
This movie was produced using images from the High Resolution Stereo Camera (HRSC) on board ESA’s Mars Express spacecraft. Its first part shows a simulated flight over the upper reaches of Ares Vallis, a large outflow channel on Mars, and parts of its source region, Iani Chaos.

Ares Vallis is one of the biggest drainage systems on Mars. From its source region in Iani Chaos near the equator, the valley winds northwest for about 1400 kilometres through the ancient Xanthe Terra highlands Eventually; it ends up in the northern lowland plains of Chryse Planitia.

The flanks of the deep canyon, rise up to 2000 meters from the valley floor. The morphology of the valley shows drainage patterns of many kinds: flow features along with isolated streamlined islands and terraces. Very likely, large amounts of water have flown here episodically during Mars’ past. Ares Vallis is thought to have formed billions of years ago.



Iani Chaos itself is a depression of approximately 200 kilometres by 180 kilometres in size. At its northern side the depression wall is eroded away to form the beginning of Ares Vallis.


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Inside Iani Chaos, a chaotic distribution of individual blocks of rock and hills form a disrupted pattern. These ‘knobs’ are several hundred metres high. Scientists suggest that they are remnants of a pre-existing landscape that collapsed after possible cavities had formed beneath the surface. Ice stored in these cavities may have been molten by volcanic heat, and the water then discharged to the north – while the highland surface collapsed as a consequence.

The 'Valleys of Mariner' are named after the Mariner 9 orbiter which first imaged this huge canyon system in 1971. From west to east, Valles Marineris stretches over 4000 kilometres along the Martian equator It is the biggest – and greatest – canyon in the Solar System: the valley floor reaches a depth of 11 kilometres.
On average, other Martian valleys are seven kilometres deep.
Large image

Image data used for this movie of the central part of Valles Marineris are from two Mars Express orbits, on 24 April and 2 May 2004, respectively, acquired from an altitude of about 500 kilometres, resulting in image resolutions of approximately 25 metres per pixel.

Here the Valles Marineris complex has its largest North-South extension. Several sub-valleys are divided by high mountain ranges, running in parallel to the entire canyon system. The two valleys seen here are named Ophir Chasma and Candor Chasma, and are each about 200 kilometres wide. The area shown in the movie is about the size of the southern half of Germany.
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