[meteorite-list] Forces of Martian Nature (Mars Express)

[Ron Baalke]

http://www.esa.int/Our_Activities/Space_Science/Mars_Express/Forces_of_martian_nature

Forces of Martian Nature
European Space Agency
10 July 2014

[Image]
The surface of Mars is pocked and scarred with giant impact craters and 
rocky ridges, as shown in this new image from ESA’s Mars Express that 
borders the giant Hellas basin in the planet's southern hemisphere.

[Image]                                                               
Hellespontus Montes in context
The Hellas basin, some 2300 km across, is the largest visible impact structure 
in the Solar System, covering the equivalent of just under half the land 
area of Brazil.  

The images presented here were taken on 13 January 2014 by the high-resolution 
stereo camera on Mars Express and feature a portion of the western rim 
of the Hellas basin, which slopes into the foreground.

This view highlights the Hellespontus Montes, a rough chain of mountain-like 
terrain that runs around the rim of the basin, seen here as an uneven 
ridge curving across the top of the main colour, topography and 3D images, 
and extending to the right in the perspective view.

This feature is a product of the final stages of the formation of the 
vast Hellas impact basin itself, most likely as the basin walls - which 
were first pushed outwards by the extraordinary forces at work during 
the formation of the basin - later collapsed and sank inwards to create 
the observed stair-stepped shape.

[Image]                                                               
Hellespontus Montes topography
Several craters throughout the scene display wrinkled and rippled features: 
the close-up of the crater in the foreground of the perspective view highlights 
a particularly interesting example where the wrinkles form a roughly concentric 
pattern, with ever-smaller arcs towards the structure's centre.

This type of feature is known as "concentric crater fill", and is thought 
to be associated with snowfall and freezing cycles in an earlier and wetter 
period of martian history.

During this period, snow fell and covered the surface and later moved 
downhill into the crater. Once inside the crater, the snow became trapped 
and soon covered by surface dust, before compacting to form ice.

The number of concentric lines indicates many cycles of this process and 
it is possible that craters like these may still be rich in ice hidden 
beneath just tens of metres of surface debris.

[Image]
Hellespontus Montes
Meanwhile, the largest impact crater in the image (top left in the main 
colour, topography and 3D images) shows a degraded, layered crater deposit 
with several "islands" of material that have been eroded by powerful winds.

Here and elsewhere in the scene, the formation of dunes building up around 
impact structures and at the base of Hellespontus Montes further indicates 
the role of strong winds shaping this scene.

Last but certainly not least, intricate valleys lead down from the Hellespontus 
Montes and weave through and across the smoother surrounding plains.

This complex region shows that many of nature’s forces have left their 
mark here over time, from the formation of the Hellas basin billions of 
years ago, to the slow and steady changes created by wind and snowfall 
over millions of years.

[Image]
Hellespontus Montes in 3D