A team led by the Finnish Meteorological Institute, with contributions from the University of Helsinki, The Open University in the UK and The National Air and Space Museum in the US, have leveraged 1970s era spacecraft data to explore the interaction of winds with surface of the desert planet Mars.
It was found the particles in a fine-grained deposit next to the lander, and exposed to the high 'winds' from the rocket exhaust during landing, are similar in size to atmospheric dust with some larger particles embedded in the material. This suggests dust is indeed very 'sticky', likely due to electrostatic forces, and able to resist entrainment by strong winds. While this reinforces the apparent paradox dust could help immobilise larger particles via electrostatic forces, along with the slower acting processes of induration, causing the dust to appear relatively mobile.
This month marks the 40th anniversary of NASA's Viking 1 spacecraft arriving in orbit at Mars on 19th June 1976. Viking lander 1 descended and landed on Mars on 20th July 1976, the first spacecraft to successful land and perform scientific investigations that included the search for life and over three Martian years of meteorological measurements.
The landing site of Viking lander 1 exhibits evidence of extensive interactions with Martian winds such as dune-like deposits consisting of fine-grained materials on top of a crusted substrate. Many questions were raised at the time of Viking, and afterwards, relating to the geological processes acting on Mars. In particular the paradox that sand-sized grains should be more easily mobilised by the wind than dust-sized particles but wide-spread dust storms are observed on Mars with sand dunes being generally unaffected by the wind.
A paper published in the June version of Icarus uses measurements made by Viking lander 1 to determine the size distribution of the particles in the fine-grained materials. Imaging of the micron sized particles is difficult on Mars and was certainly not possible with the Viking lander cameras. Instead a thermal measurement technique was used by the authors in combination with other indirect measurements made by Viking lander 1.
Paton, M. D., Harri, A.-M., Savijärvi, H., Mäkinen, T., Hagermann, A., Kemppinen, O. and Johnston, A., Thermal and microstructural properties of fine-grained material at the Viking Lander 1 site, Icarus, 271, 360-374 (2016)
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