Following up on bits and pieces of news, I periodically find myself on one of the Mars imagery sites, lost in wonder; it’s a time-consuming process. So, I thought, why not, again, lure readers of this blog to accompany me on these extraordinary journeys? Scientific Frontline, a site that I just discovered, compiles a wide variety of images into all kinds of galleries, not just of things extraterrestrial. It’s from there that the stunning image above comes, originally, of course, from NASA/JPL/University of Arizona and the Mars Reconnaissance Orbiter. The description is as follows:
Dunes within a crater on Mars are visible in this HiRISE image. This crater is located in the southern hemisphere where it was winter at the time this image was taken.
This observation documents new seasonal processes occurring on dunes at this latitude, as well as other interesting phenomena. The bright tones are interpreted as carbon dioxide or water frost. This is generally concentrated on the east-facing slopes of the dunes, which are in shadow and therefore cooler. Some dark spots on the dunes may be areas that have defrosted more than surrounding terrain.
Landslides and dark-toned streaks are seen on many of the west-facing dune slopes. The general dune morphology indicates formation by westerly winds. However, zooming in on the image shows smaller scale ripples that appear to have been formed by winds blowing from the south and north.
[Written by: Nathan Bridges & Kelly Kolb]
And, speaking of winter dunes, direct from the high resolution imaging site at the University of Arizona:
Mars has a vast sea of sand dunes in the high latitude region encircling its North polar cap, known as the North polar erg. These dunes are made up of basalt and gypsum sand grains. In some regions of the North polar erg where the sand supply is limited they take on an elongated crescent shape. The icy ground that the dunes are on top of has irregular polygonal patterns. In other areas with an abundant supply of sand the dunes are continuous (see also PSP_007494_2580).
The entire North polar erg is covered in the winter with a seasonal polar cap composed of carbon dioxide (dry ice). In the spring time this seasonal polar cap evaporates.
[Written by: Candy Hansen]
And then, off we go into the stunning landscapes of the planet (it’s clearly not geomorphology, but does anyone know the correct term?)
This observation shows a portion of the central sedimentary deposits in Pasteur Crater.
The deposits in this image now being eroded into knobs and ridges. The erosion is probably dominated by wind, as most of the ridges are parallel. This is common in wind-eroded features, with the ridges generally aligned with the prevailing wind.
At high resolution, layering is revealed in many of the knobs and outcrops. The horizontal layers indicate that the material was deposited uniformly over a broad area. Possible origins include volcanic airfall or lacustrine (lake) deposits. After deposition, the rock in this area has been fractured and faulted, forming a diverse array of cracks.
The mottled appearance of much of the image is caused by dark, featureless patches which may be wind-blown dust. These have interacted with lighter-toned ridges and ripples which are probably also formed by aeolian (wind) processes. In places, the dark patches partially cover the ripples, indicating that they have moved more recently, but they must be thin because the ripples frequently stand above surrounding dark material.
The ripples exhibit multiple interacting orientations in some places, producing networks of small ridges which reflect movement in winds from several directions.
[Written by: Colin Dundas]
We should not forget the European Space Agency project – the Mars Express high resolution stereo-photography and mineral mapping mission (whose lander, the Beagle 2, so ignominiously plummeted to the surface of Mars in 2003). The imaging orbiter was originally expected to have a relatively short life, but its operations have been extended several times and are continuing; its recent image of Orcus Patera, a mysteriously elongated crater, has been in the news last week ("scientists are baffled..."). I particularly like the image below (I have inserted a perspective detail) from early on in the mission: a dune field in the crater Argyre Planitia. I assume that the dark colour results from basaltic sands being constantly reworked by the winds as opposed to being covered in dust, but why is the dune field so compact and isolated? A reflection of the complex wind circulation patterns? Note that 3D images are available from the website.
These images, taken by the High Resolution Stereo Camera (HRSC) on board ESA's Mars Express spacecraft, show a Martian crater with a dune field on its floor.
The images were taken during orbit 427 in May 2004, and show the crater with a dune field located in the north-western part of the Argyre Planitia crater basin.
The images are centred at Mars longitude 303° East and latitude 43° South. The image resolution is approximately 16.2 metres per pixel. The crater is about 45 kilometres wide and 2 kilometres deep. In the north-eastern part of this crater, the complex dune field is 7 kilometres wide by 12 kilometres long. In arid zones on Earth, these features are called ‘barchanes’, [sic: they mean, of course, “barchans”] which are dunes having an asymmetrical profile, with a gentle slope on the wind-facing side and a steep slope on the lee-side. The dune field shown here suggests an easterly wind direction with its steeper western part. The composition of the dune material is not certain, but the dark sands could be of basaltic origin.
Enough, I must stop – good luck!