Starship Asterisk*

Candy Hansen wrote:

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Seasonal Erosion (ESP_029545_0950) (video)

Bright carbon dioxide frost (or, dry ice) highlights this network of channels carved into the surface. The channels are eroded a little bit every spring when the seasonal polar cap, composed of dry ice, sublimates (meaning going directly from a solid to gas) at the ice-surface interface. The erosion occurs under the seasonal ice layer: when trapped pressurized gas finds an escape route it carries along loose surface material. This surface material is blown downwind and deposited in dark fans on top of the seasonal ice layer.

The trapped gas finds the weakest easiest escape route. In this area the gas exploited the existing polygonal structure of the surface below. Polygonal terrain is common at high latitudes, and is caused by the thermal contraction and expansion of water ice frozen in the surface dirt.

Alfred McEwen wrote:

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A Channel Emanating from a Crater (ESP_029877_2160) (video)

The origins of channels on Mars is of great interest to understand the history of water.

There are several large (more than 30 kilometers wide) craters on Mars that appear to have spawned channels, perhaps draining from the fresh, hot impact ejecta.

Visible here is a well-preserved (meaning geologically young) crater that is about 3 kilometers wide, and a channel that appears from the margins of the ejecta and flows to the south. Did this small crater generate this relatively large channel?

Most likely the channel was there first, and the crater is younger. However, the channel might have been generated by a larger crater to the northwest.

Nathan Bridges wrote:

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Changing Dust Devil Tracks and Sand Streaks in Noachis Terra (ESP_030014_1245) (video)

Sand dunes on Mars are studied for many reasons. Recent investigations have focused on dune and ripples movement.

In this observation, we look at dunes within a crater in Noachis Terra. Zooming in to one of these areas (and here is the context image) we see the edges of two dunes separated by a field of ripples and rocks. We can compare this area to another image taken two Mars years ago. In the older image, there are many dark wispy features that cover the dunes. These are dust devil tracks, which formed when vortices removed a thin layer of dust off the surface, revealing a darker substrate.

In addition, there are dark sand streaks extending westward from the eastern dune. Blinking between these images shows that virtually all traces of the dust devil tracks and dark streaks have disappeared in the two Mars years. There is also little evidence for dune or ripple movement (however, these images have not yet been orthorectified for a detailed analysis).

In this region, it is likely that dust is periodically deposited and then removed off the dunes. The presence of dust may shield the dunes and ripples from significant movement, such that the observed changes are but thin layers of dust being removed and minor sand streaks that blow off the dunes.

This is a stereo pair with ESP_030080_1245.

Alfred McEwen wrote:

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The Tracks of Curiosity (ESP_030168_1755) (video)

This image was acquired for color coverage of the region that the Curiosity rover may explore, but we acquired some extra RED (monochromatic) coverage of the rover tracks.

This image shows the entire distance traveled from the landing site (dark smudge at left) to its location as of 2 January 2013 (the rover is bright feature at right). The tracks are not seen where the rover has recently driven over the lighter-toned surface, which may be more indurated than the darker soil.