File:Seasonal processes in the Northern polar dunes with Flow Like Features.gif

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English: Time differences between the images are 22 days and 12 days. The final picture shows a long feature that formed new between the two images, and its length is 60 meters so it grew at a rate of at least 5 meters per day.[1]

The features progress through a sequence of changes, first wind blown, and then seepage features associated with the dune spots, and then finally, dark seepage features appear all along the dune crest as in this sequence. These images show the final stage, growth of the seepage features all along the dune crest. [1]

These features form at a surface temperature of -90°C, and increase at between 0.3 meters and 7 meters a day. Proposed models for the features in this hemisphere predict liquid brines even in these low temperatures.[2][1]

Shortwave solar radiation can efficiently penetrate the translucent surface layer. This raises the temperature of the underlying surface and the dark ejecta, and the models predict that the temperatures can be raised high enough to melt the ice, which could then form brines on ice / salt interfaces. [3]

An alternative mechanism for the Northern hemisphere involves dry ice and sand cascading down the slope but most of the models involve cold liquid brines.[2]

I created this animation myself by combining the following HiRise images from NASA/JPL/University of Arizona, all taken in 2008:

PSP_007758_2575 - 22 March (2:06 PM) , sol 101

PSP_007903_2575 - 3rd April (2:07 PM), sol 113

(found the sols using the Earth date to Martian solar longtitude converter)
Date
Source http://www.uahirise.org/PSP_007903_2575
Author NASA/JPL/University of Arizona

Licensing

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Public domain This file is in the public domain in the United States because it was solely created by NASA. NASA copyright policy states that "NASA material is not protected by copyright unless noted". (See Template:PD-USGov, NASA copyright policy page or JPL Image Use Policy.)
Warnings:
  1. ↑ a b c Kereszturi, A., et al. "Indications of brine related local seepage phenomena on the northern hemisphere of Mars." Icarus 207.1 (2010): 149-164.
  2. ↑ a b (2013). "Water and Brines on Mars: Current Evidence and Implications for MSL". Space Science Reviews 175 (1-4): 29–51. DOI:10.1007/s11214-012-9956-3. ISSN 0038-6308.
  3. ↑ (2013). "Water and Brines on Mars: Current Evidence and Implications for MSL". Space Science Reviews 175 (1-4): 29–51. DOI:10.1007/s11214-012-9956-3. ISSN 0038-6308. ""Martinez et al. (2012) show that the formation of brines is consistent with the low temperatures measured by TES and THEMIS when they form (≤180 K), if the spatial resolution and optical properties of the translucent CO2 ice layer are considered. The resolution of TES is much coarser than the dimensions of the dark spots and FLF. In addition, TES and THEMIS measurements of the surface temperature are in the thermal infrared band, where CO2 ice is opaque. Since the fractional area covered by dark spots and FLF (composed of dark material above the CO2 ice layer), is much smaller than that covered by CO2 ice in TES and THEMIS pixels, they predominantly measure the low brightness temperature associated with the CO2 ice layer, not the temperature of the dark spots and FLF. As postulated by the gas venting model, shortwave solar radiation can efficiently penetrate the translucent CO2 ice layer. Thus, both the underlying surface and the dark ejecta can reach temperatures much higher than those measured by TES and THEMIS (Martinez et al. 2012). Also, subsurface melt water and ULI water can form in the shallow subsurface at temperatures as low as 180 K (see Sect. 2). Salts in contact with these types of liquid water could form liquid brines, and thus help explain the evolution of dune dark spots and FLF.""

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