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Exploring Mars: Mysteries in Nili Fossae

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Posted January 23, 2015

These new images from the high-resolution stereo camera on ESA’s Mars Express show Nili Fossae, one of the most enticing regions on Mars. This ‘graben system’ lies northeast of the volcanic region of Syrtis Major on the northwestern edge of the large Isidis impact basin – and intriguing hints of methane have been seen here.

The Nili Fossae graben system, part of which is shown in this image, is an area of great geological interest near the giant Isidis impact basin, northeast of the Syrtis Major volcanic province. Copyright ESA/DLR/FU Berlin, CC BY-SA 3.0 IGO

The Nili Fossae graben system, part of which is shown in this image, is an area of great geological interest near the giant Isidis impact basin, northeast of the Syrtis Major volcanic province. Copyright ESA/DLR/FU Berlin, CC BY-SA 3.0 IGO

Grabens are blocks of land that have fallen between parallel faults, sometimes forming rift valleys. The graben system in Nili Fossae contains numerous troughs oriented concentrically around the edges of an impact basin, as can be seen in the context map.

The easternmost of these troughs is partially visible at the lower left of the images. It is perhaps most obvious as a depression in the topography map from Mars Express.

A wider contextual image showing the region around Nili Fossae. The Nili Fossae graben system is an area of great geological interest near the giant Isidis impact basin (part of which is seen in the lower right portion of this map), northeast of the Syrtis Major volcanic province. It is centred on 75°E / 24°N. The region was imaged by the High Resolution Stereo Camera on ESA’s Mars Express on 16 October 2014 during orbit 13699.   Copyright NASA MGS MOLA Science Team

A wider contextual image showing the region around Nili Fossae. The Nili Fossae graben system is an area of great geological interest near the giant Isidis impact basin (part of which is seen in the lower right portion of this map), northeast of the Syrtis Major volcanic province. It is centred on 75°E / 24°N. The region was imaged by the High Resolution Stereo Camera on ESA’s Mars Express on 16 October 2014 during orbit 13699. Copyright NASA MGS MOLA Science Team

The graben is most likely associated with the formation of the Isidis impact basin. Flooding of the basin with basaltic lava may have resulted in subsidence, which added stress to the planet’s crust and was then released through fracturing and trough formation.

Mars Express and other spacecraft have shown that the region displays a fascinating mineral diversity, drawing the attention of many planetary scientists. The minerals include phyllosilicates (clays), carbonates and opaline silica. These indicate a diverse history for this area resulting from the huge geological and tectonic forces that have been at play.

The graben system contains numerous troughs, one of which can be seen crossing the lower left of this image. On the plateau above, several depressions can be seen, some of them extending into the trough. A large, 55 km-diameter impact crater with a central pit can be seen on the right. This colour-coded topographic view is based on a digital terrain model of the region, from which the topography of the landscape can be derived. White and red show the highest terrains, while blue and purple show the deepest. Copyright ESA/DLR/FU Berlin, CC BY-SA 3.0 IGO

The graben system contains numerous troughs, one of which can be seen crossing the lower left of this image. On the plateau above, several depressions can be seen, some of them extending into the trough. A large, 55 km-diameter impact crater with a central pit can be seen on the right.
This colour-coded topographic view is based on a digital terrain model of the region, from which the topography of the landscape can be derived. White and red show the highest terrains, while blue and purple show the deepest. Copyright ESA/DLR/FU Berlin, CC BY-SA 3.0 IGO

Water has played an important role here, too. The visible trough’s flanks are very steep (see the topography map) and some layered materials can be spotted at the walls. On the plateau, several depressions can be observed. Some of them appear to extend into the trough and show a resemblance to small ‘sapping valleys’.

Sapping valleys develop when groundwater removes material from underneath the surface. This gradually relocates the spring line further upstream, carving a valley in the process.

This image was acquired by the High Resolution Stereo Camera on ESA’s Mars Express on 16 October 2014 during orbit 13699. This oblique perspective view was generated using data from the stereo channels. The centre of the associated main colour image is located at about 75°E / 24°N. The ground resolution is about 18 m per pixel. North is to the right, east is up. Copyright ESA/DLR/FU Berlin, CC BY-SA 3.0 IGO

This image was acquired by the High Resolution Stereo Camera on ESA’s Mars Express on 16 October 2014 during orbit 13699. This oblique perspective view was generated using data from the stereo channels. The centre of the associated main colour image is located at about 75°E / 24°N. The ground resolution is about 18 m per pixel. North is to the right, east is up. Copyright ESA/DLR/FU Berlin, CC BY-SA 3.0 IGO

The images also contain evidence for percolating hydrothermal fluids in the subsurface of the region. A large, 55 km-diameter impact crater with a central pit is clearly seen in the main colour, topography and 3D images. The pit is believed to have been excavated when water or ice, trapped below the surface, was rapidly heated by the impact that shaped the crater. The sudden heating caused a violent steam explosion that either weakened the rocky surface, leading to its collapse, or it may even have blasted it away, leaving the rocky hole and rocky debris.

This anaglyph image, which provides a 3D view of the landscape when viewed using stereoscopic glasses with red–green or red–blue filters, was derived from data acquired by the nadir channel and one stereo channel of the High Resolution Stereo Camera on ESA’s Mars Express. Copyright ESA/DLR/FU Berlin, CC BY-SA 3.0 IGO

This anaglyph image, which provides a 3D view of the landscape when viewed using stereoscopic glasses with red–green or red–blue filters, was derived from data acquired by the nadir channel and one stereo channel of the High Resolution Stereo Camera on ESA’s Mars Express. Copyright ESA/DLR/FU Berlin, CC BY-SA 3.0 IGO

In addition to the variety of interesting geological features, Nili Fossae is of particular interest because it is a site where atmospheric methane may have been detected by Earth-based telescopes. Methane may be produced here, but its origin remains mysterious, and could be geological or perhaps even biological.

There is certainly a huge amount to study here. Nili Fossae was on the shortlist of landing sites for NASA’s Curiosity rover, even though ultimately the choice was made to send the robotic explorer to Gale Crater.

Source: ESA

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