[meteorite-list] Mars Crater Shows Evidence For Climate Evolution (Mars Express)

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu, 7 Jun 2012 13:40:59 -0700 (PDT)
Message-ID: <201206072041.q57Kexse001833_at_zagami.jpl.nasa.gov>

http://www.esa.int/esaSC/SEMD285XX2H_index_0.html

Mars crater shows evidence for climate evolution
European Space Agency
7 June 2012

ESA's Mars Express has provided images of a remarkable crater on Mars
that may show evidence that the planet underwent significant periodic
fluctuations in its climate due to changes in its rotation axis.
 
On 19 June 2011, Mars Express pointed its high-resolution stereo camera
at the Arabia Terra region of Mars, imaging the Danielson and Kalocsa
craters.

Danielson crater is named after the late George E Danielson, who was
instrumental in the development of many spacecraft cameras flown to
Mars. Seen to the right (north) in the image, it is the larger crater,
roughly 60 km across.

Kalocsa crater lies in the centre of the image and is smaller, about 33
km in diameter and a kilometre shallower than Danielson. It is named
after a town in Hungary famed for its astronomical observatory.
 
[Image]
Danielson and Kalocsa craters context
 
Danielson crater, like many in the Arabia Terra region, is filled with
layered sediments, which in this instance have been heavily eroded over
time. Within the crater are peculiarly layered buttes, known as yardangs.

Yardangs are streamlined hills carved from bedrock or any consolidated
or semi-consolidated material by abrasive dust and sand particles
carried in the wind.

They are seen on Earth in desert regions, with notable examples in North
Africa, Central Asia and Arizona in the United States.

[Image]
Danielson and Kalocsa context
 
In the case of Danielson crater, it is believed that sediments were
cemented by water, possibly from an ancient deep groundwater reservoir,
before being eroded by the wind.

The orientation of the yardangs leads scientists to theorise that strong
north-northeasterly winds (from the lower right in the image) both
deposited the original sediments and then caused their subsequent
erosion in a later drier period of martian history.

A 30 km-long field of darker dunes can be seen bisecting the yardangs
and is thought to have formed at a later epoch.
 
[Image]
Danielson and Kalocsa topography
 
The crater floor of Danielson shows evidence for a series of alternating
sedimentary layers with roughly uniform thickness and separation.

Some scientists believe that this indicates periodic fluctuations in the
climate of Mars, triggered by regular changes in the planet's axis of
rotation. The different layers would have been laid down during
different epochs.

By marked contrast, Kalocsa crater shows a completely different topography.

Here, no layered sediments are seen. This is thought to be due to the
higher altitude of its floor, with the crater not tapping in to the
suspected underlying ancient water reservoir.

Another hypothesis is that this crater is younger than its neighbour,
created when water was not present anymore.
 

[Image]
Danielson and Kalocsa 3D anaglyph
 
Received on Thu 07 Jun 2012 04:40:59 PM PDT