[meteorite-list] Mars glaciers

From: Darren Garrison <cynapse_at_meteoritecentral.com>
Date: Mon Mar 21 13:24:58 2005
Message-ID: <ko4m31dnc3fhn0l9kn3t2ou43ncl3v9ej5_at_4ax.com>

http://www.innovations-report.com/html/reports/physics_astronomy/report-41996.html



?Hourglass? shaped craters filled traces of glacier

This image, taken by the High Resolution Stereo Camera (HRSC) on board ESA?s Mars Express
spacecraft, shows flow features most likely formed by glaciers or ?block? glaciers.

This unusual ?hourglass?-shaped structure is located in Promethei Terra at the eastern rim of the
Hellas Basin, at about latitude 38? South and longitude 104? East. A so-called ?block? glacier, an
ice stream with a large amount of scree (small rocks of assorted sizes), flowed from a flank of the
massif into a bowl-shaped impact crater (left), nine kilometres wide, which has been filled nearly
to the rim. The block glacier then flowed into a 17 kilometre wide crater, 500 metres below, taking
advantage of downward slope.

The Martian surface at mid latitudes and even near the equator was being shaped by glaciers until a
few million years ago. Today, water ice could still exist at shallow depths as ?fossil? remnants of
these glaciers.

Numerous concentric ridges are visible and appear similar to ?end moraines? (hills of scree that
form as an extending glacier pushes material ahead and remain after its retreat). Furthermore, there
are parallel stripe-like structures that are interpreted as middle moraines, displaying the flow
direction of these glaciers. In locations where glaciers creep over steep terrain, cracks are
visible. Similarly in terrestrial glaciers, cracks are formed when tensile stress within the ice
increases due to greater slope and uneven terrain.

Further glacial features include elongated grooves, extending several kilometres, and elongated
hills observed on the surface of mountain ridges some distance from potentially glaciated areas.
These hills could be analogous to so-called ?drumlins?, structures formed beneath ice by glacial
flow resulting in compression and accumulation of abraded material. On Earth, drumlins appear in
formerly glaciated regions such as Germany?s Bavarian alpine uplands. These glacial structures are
seen in a consistent spatial context, confirming the belief that scientists are really seeing former
glaciers on Mars.

Of particular interest is the age of these glacially shaped surfaces, which seem to be fairly intact
over a wide area of the formerly glaciated terrain. Typical evidence for a significant loss of ice
volume, such as ?kettle holes? present in ice-free regions of Iceland, are almost entirely missing.
The statistical analysis of the number of craters formed by meteorite impacts used for age
determination also shows that part of the surface with its present-day glacial characteristics was
formed only a few million years ago. In planetology, this age range is considered extremely young.

In these latitudes, ice on the surface of Mars is not stable over a long period of time due to the
extremely thin atmosphere. In theory it is cold enough to allow for the existence of glaciers at the
equator ? summer day temperatures rise to a maximum of 20? C while night and winter time
temperatures often drop below minus 50? C. But under the prevailing atmospheric pressure, ice would
sublimate (transform directly from solid to gaseous state), and then escape from the atmosphere into
outer space.

Therefore, glaciers must have formed until a few million years ago, in a time that was warmer and
possibly also had a thicker atmosphere, and then became inactive or retreated due to the lack of
continued supply of ice. Since then, they have been protected from sublimation by a thin dust layer.
On Mars, dust is almost ubiquitous and would explain why ?fossil? ice present at depths of only a
few metres could not be detected by other instruments such as spectrometers.

If these conclusions prove to be true, the results would indicate a climate change on Mars within
the last million years. Such a dramatic climate change has been discussed for some years by Mars
researchers. It could have been caused by a shift in the polar axis of the planet over millions of
years ? a phenomenon long known to scientists. Martian climate history is one of the main areas that
ESA?s Mars Express can help to decipher.

 
Received on Fri 18 Mar 2005 12:43:53 PM PST