[meteorite-list] Ice-coated Beauty in Mars' Silver Island (Mars Express)

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu, 4 Oct 2012 12:03:11 -0700 (PDT)
Message-ID: <201210041903.q94J3BOR007935_at_zagami.jpl.nasa.gov>

http://www.esa.int/esaCP/SEM8GXERI7H_index_0.html

Ice-coated beauty in Mars' Silver Island
European Space Agency
4 October 2012

On 8 June, the high-resolution stereo camera on Mars Express captured a
region within the 1800 km-wide and 5 km-deep Argyre basin, which was
created by a gigantic impact in the planet's early history.
 
After Hellas, the Argyre impact basin is the second largest on the Red
Planet.

[Image]
Argyre and Hooke Crater perspective view
 

The name stems from the Greek word "argyros" (silver) and Argyre was an
"island of silver" in Greek and Roman mythology. Giovanni Schiaparelli,
the famed Italian astronomer, gave the name to this bright region on
Mars in his detailed 1877 map.

At the centre of the larger impact basin is a flat region known as
Argyre Planitia. The Mars Express images in this release all show a
portion of the northern part of this plain, with a large portion of each
image dominated by the western half of the 138 km-wide Hooke Crater,
named after the British physicist and astronomer Robert Hooke.
 

[Image]
Argyre and Hooke Crater in context
        
Most of Argyre Planitia has been shaped by wind, glacial and lacustrine
(lake-based) processes, creating the smoother appearance of the
landscape surrounding Hooke Crater.

Inside Hooke Crater itself, prevailing wind activity has formed dunes
and helped to create linear erosion features, clearly seen in the
following topographic image.
 
[Image]
Topographical view Argyre Planitia
 
The most striking feature of this image release, shown clearly in the
first image at the top of the page, is the icing sugar-like covering of
the surface to the south (left) of the image. This is frost, but made of
carbon dioxide, not water.

Carbon dioxide ice is commonly seen on the surface of Mars, and has long
been thought to form only at ground level, freezing out of the
atmosphere as frost, which is most likely the case here.
 
[Image]
3D anaglyph view Hooke Crater
 
The lowlands to the south (left in the first image) of Hooke and regions
within the crater are covered by a thin ice layer. However, it is
lacking on the inner north-facing crater wall. It was probably melted
there by the Sun, as indicated by the timing of the image.

Taken at around 4:30 in the local afternoon and during the southern
hemisphere's mid-winter, the Sun would have been just over 20 degrees
above the horizon. It should then have been able to melt ice on the
steeper north-facing slopes, but would probably not have had enough time
to warm and melt any on low-lying horizontal surfaces.

Schiaparelli would doubtless have marvelled at the exquisite images
coming back from Mars Express, which continues to provide today's
scientists with a bounty of wonderful data.
 
Received on Thu 04 Oct 2012 03:03:11 PM PDT