Physics
Scientific paper
Dec 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufm.u11b0028m&link_type=abstract
American Geophysical Union, Fall Meeting 2008, abstract #U11B-0028
Physics
5415 Erosion And Weathering, 5420 Impact Phenomena, Cratering (6022, 8136), 5460 Physical Properties Of Materials
Scientific paper
Unique from past planetary surface missions, the Phoenix spacecraft used pulsed retro-rockets to land on the northern polar region of Mars. Mainly viscous shear erosion caused by descent jets had minimally altered previous landing sites. Here we report novel simulations of surface modification by pulsed thruster plumes, and assess the erosion processes leading to the first exposure of ice below the Martian regolith. At Mars atmospheric pressure, we find that the repetitive injection of high pressure gas into porous soil by the pulsed engines leads to the propagation of cyclic radial shock waves within the soil. We show that these shock waves cause 'explosive erosion' and excavate the regolith down to the ice table in a radius of ~75 cm under the lander. Moreover, coarse and fine particles are ejected outward to a radius of 3 m and ~20 m from the thrusters, respectively. The results of our simulations are confirmed by images of the Phoenix landing site and provide important insights into the geology, glaciology and geomorphology of the landing site. These erosion dynamics may lead to ammonia hydrates and ammonium salts, but may demonstrate limited soil contamination. By comparing results from the landing site and our simulations, we come to the initial conclusions that the Martian arctic regolith has high porosity and permeability, mixture of fines with coarse particles, and exhibit cohesive stresses greater than 0.9 kPa.
Grover Rob M.
Mehta Mridul
Renno Nilton O.
Sengupta Anirvan
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