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Title: Evolution of major sedimentary mounds on Mars
Author: Edwin S. Kite, Jonathan Sneed, David P. Mayer, Kevin W. Lewis, Timothy I. Michaels, Alicia Hore, Scot C.R. Rafkin

We present a new database of >300 layer-orientations from sedimentary mounds on Mars. These layer orientations, together with draped landslides, and draping of rocks over differentially-eroded paleo-domes, indicate that for the stratigraphically-uppermost ~1 km, the mounds formed by the accretion of draping strata in a mound-shape. The layer-orientation data further suggest that layers lower down in the stratigraphy also formed by the accretion of draping strata in a mound-shape. The data are consistent with terrain-influenced wind erosion, but inconsistent with tilting by flexure, differential compaction over basement, or viscoelastic rebound. We use a simple landscape evolution model to show how the erosion and deposition of mound strata can be modulated by shifts in obliquity. The model is driven by multi-Gyr calculations of Mars' chaotic obliquity and a parameterization of terrain-influenced wind erosion that is derived from mesoscale modelling. Our results suggest that mound-spanning unconformities with kilometers of relief emerge as the result of chaotic obliquity shifts. Our results support the interpretation that Mars' rocks record intermittent liquid-water runoff during a >10^8-yr interval of sedimentary rock emplacement.

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A record of ancient tectonic stress on Mars

Sets of ridges and troughs some 1000 km north of the giant Olympus Mons volcano contain a record of the intense tectonic stresses and strains experienced in the Acheron Fossae region on Mars 3.7-3.9 billion years ago.
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Arcadia Planitia
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Title: Widespread Excess Ice in Arcadia Planitia, Mars
Author: Ali M. Bramson, Shane Byrne, Nathaniel E. Putzig, Sarah Sutton, Jeffrey J. Plaut, T. Charles Brothers, John W. Holt

The distribution of subsurface water ice on Mars is a key constraint on past climate, while the volumetric concentration of buried ice (pore-filling versus excess) provides information about the process that led to its deposition. We investigate the subsurface of Arcadia Planitia by measuring the depth of terraces in simple impact craters and mapping a widespread subsurface reflection in radar sounding data. Assuming that the contrast in material strengths responsible for the terracing is the same dielectric interface that causes the radar reflection, we can combine these data to estimate the dielectric constant of the overlying material. We compare these results to a three-component dielectric mixing model to constrain composition. Our results indicate a widespread, decameters-thick layer that is excess water ice ~10^4 km^3 in volume. The accumulation and long-term preservation of this ice is a challenge for current Martian climate models.

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Mars may have had continental crust like ancient Earth

Rocks similar to some of the oldest continental crusts on Earth have been discovered on the surface of Mars by NASA's Curiosity rover.
The findings, reported in the journal Nature Geoscience, provide new insights into how Mars formed and evolved early in its history.
 
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Curiosity Finds Iron Meteorite on Mars

This rock encountered by NASA's Curiosity Mars rover is an iron meteorite called "Lebanon," similar in shape and luster to iron meteorites found on Mars by the previous generation of rovers, Spirit and Opportunity. Lebanon is about 2 yards or 2 meters wide (left to right, from this angle). The smaller piece in the foreground is called "Lebanon B."
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Martian Methyl Chloride
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Title: Martian Methyl Chloride. A lesson in uncertainty
Authors: William Bains

The MSL Lander Curiosity has recently detected methyl halides coming from heated samples of Martian soil. This is reminiscent of similar findings in the Viking Lander spacecraft. In the 1970s a consensus developed quickly explaining the methyl halides as contamination originating from the spacecraft, and ignoring lines of evidence that the two compounds originated from Mars, and that they could not have originated from the proposed spacecraft chemistry. I discuss why this consensus developed from the understanding of biochemistry and geochemistry of 1976, despite its implausibility. Subsequent explanations for the Viking methyl halides are more plausible but still not proven. The Curiosity rover results are also being explained as a result of on-spacecraft chemistry. I urge caution in this interpretation, in light of the historical Viking example: it is better to leave unexplained data unexplained than to lock in an explanation that precludes future developments.

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Ridges on Mars suggest ancient flowing water

Ridges in impact craters on Mars appear to be fossils of cracks in the Martian surface, formed by minerals deposited by flowing water. Water flowing beneath the surface suggests life may once have been possible on Mars.
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Rover's 'SAM' Lab Instrument Suite Tastes Soil

A pinch of fine sand and dust became the first solid Martian sample deposited into the biggest instrument on NASA's Mars rover Curiosity: the Sample Analysis at Mars, or SAM.
Located inside the rover, SAM examines the chemistry of samples it ingests, checking particularly for chemistry relevant to whether an environment can support life. Curiosity's robotic arm delivered SAM's first taste of Martian soil to an inlet port on the rover deck on Nov. 9. During the following two days, SAM used mass spectrometry, gas chromatography and laser spectrometry to analyse the sample.

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Curiosity Mars rover finds soil similar to Hawaii's

Nasa's Curiosity rover has found soil on Mars to be similar to Hawaii's after sifting and scanning its first sample on the Red Planet.
The robot's CheMin instrument shook out fine particles of soil and fired X-rays at them to determine their composition.

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Planetary Tectonics demonstrated by An Yin & Robin Reith



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