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The Phoenix mission investigated patterned ground and weather in the northern arctic region of Mars for 5 months starting 25 May 2008 (solar longitude between 76.5 degrees and 148 degrees ). A shallow ice table was uncovered by the robotic arm in the center and edge of a nearby polygon at depths of 5 to 18 centimeters. In late summer, snowfall and frost blanketed the surface at night; H(2)O ice and vapor constantly interacted with the soil. The soil was alkaline (pH = 7.7) and contained CaCO(3), aqueous minerals, and salts up to several weight percent in the indurated surface soil. Their formation likely required the presence of water.
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... University Valley is of special interest as an analogue for Mars environmental and habitability studies. While dry permafrost is rare on Earth, it is widespread on Mars, where dry permafrost begins at the surface and is underlain by ice-cemented ground (Mellon & Jakosky 1993, Mellon et al. 2009, Smith et al. 2009, Mellon & Sizemore 2021. The Antarctic Dry Valleys represent one of the driest and coldest places on Earth, and as such they provide an interesting comparison point to conditions in the Martian subsurface. ...
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... Viking 2 in 1976 (Jones et al., 1979) and Phoenix in 2008 (Mellon et al., 2009). ...
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... In 2002, data from the Odyssey orbiter confirmed the current existence of subsurface water ice deposits on Mars (Boynton et al. 2002); and in 2008, data from the Phoenix lander confirmed the existence of water ice currently on the surface in the polar regions of Mars (Smith et al., 2009). In 2015, the existence of hydrated salts of perchlorate and chlorate were discovered in the equatorial regions of Mars (Ojha et al., 2015). ...
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We examine potentially periglacial landforms in Mars Orbiter Camera (MOC) and High Resolution Imaging Science Experiment (HiRISE) images at the Phoenix landing site and compare them with numerical models of permafrost processes to better understand the origin, nature, and history of the permafrost and the surface of the northern plains of Mars. Small-scale (3-6 m) polygonal-patterned ground is ubiquitous throughout the Phoenix landing site and northern plains. Larger-scale (20-25 m) polygonal patterns and regularly spaced (20-35 m) rubble piles (localized collections of rocks and boulders) are also common. Rubble piles were previously identified as ``basketball terrain'' in MOC images. The small polygon networks exhibit well-developed and relatively undegraded morphology, and they overlay all other landforms. Comparison of the small polygons with a numerical model shows that their size is consistent with a thermal contraction origin on current-day Mars and are likely active. In addition, the observed polygon size is consistent with a subsurface rheology of ice-cemented soil on depth scales of about 10 m. The size and morphology of the larger polygonal patterns and rubble piles indicate a past episode of polygon formation and rock sorting in thermal contraction polygons, while the ice table was about twice as deep as it is presently. The pervasive nature of small and large polygons, and the extensive sorting of surface rocks, indicates that widespread overturning of the surface layer to depths of many meters has occurred in the recent geologic past. This periglacial reworking has had a significant influence on the landscape at the Phoenix landing site and over the Martian northern plains.
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