Free Astronomy Magazine January-February 2018

16 JANUARY-FEBRUARY 2018 SPACE CHRONICLES Fracture swarms on Mars by ESA P erspective view of fractures in Sirenum Fossae in the southern hemisphere of Mars. The view shows the movement of the crust, likely in response to the tectonic stresses linked to volcanic activity of the wider region. In this kind of sce- nario, fractures divide the crust into blocks: movement along a pair of faults causes the centre section to drop down into ‘graben’. The scene is part of the region imaged on 5 March 2017 during Mars Express orbit 16688. The ground resolution is about 14 m/pixel and the images are centred at 28°S / 215°E. North is to the right. [ESA/DLR/FU Berlin, CC BY-SA 3.0 IGO] T hese striking features on Mars were caused by the planet’s crust stretching apart in re- sponse to ancient volcanic activity. The fractures in the Sirenum Fossae region in the southern hemisphere were imaged by ESA’s Mars Express in March. They extend for thousands of kilometres in length, far beyond the boundaries of this image. The fractures divide the crust into blocks: the movement along a pair of faults causes the centre section to drop down into ‘graben’ several kilome- tres wide and a few hundred metres deep. Elevated blocks of crust re- main between the graben when there is a parallel series of fault, as seen in this scene. The Sirenum Fos- sae are part of a larger radial frac- ture pattern around the Arsia Mons volcano in the Tharsis region, which is situated some 1800 km to the northeast. Tharsis is the largest vol-