Chemically striking regions on Mars and Stealth revisited

Abstract

The Mars Odyssey Gamma Ray Spectrometer Suite has yielded global chemical information for Mars. In this work, we establish regions of unusual chemical composition relative to average Mars primarily on the basis of Ca, Cl, Fe, H, K, Si, and Th. Using data from Mars Odyssey; the Mars Exploration Rovers; the Mars Reconnaissance Orbiter Imaging; and 3.5 cm and 1.35 cm radar observations from Earth, we examine a chemically striking ≈2.E6 km2 region and find it to overlap significantly with a radar Stealth region on Mars. It is remarkably enriched in Cl and depleted in Fe and Si (along with minor variations in H, K, and Th) relative to average Mars. Surface dust observed at the two rover sites mixed with and indurated by Ca/Mg‐bearing sulfate salts would be a reasonable chemical and physical analog to meter‐scale depths. We describe potential scenarios that may have contributed to the unique properties of this region. The bulk dust component may be an air fall deposit of compositionally uniform dust as observed in situ. Hydrothermal acid fog reactions on the flanks of nearby volcanoes may have generated sulfates with subsequent deflation and transport. Alternatively, sulfates may have been produced by low‐temperature, regional‐scale activity of ground ice–driven brine and/or regional‐scale deposition of acidified H2O snowfall.

Aeolian bedforms, yardangs, and indurated surfaces in the Tharsis Montes as seen by the HiRISE Camera: Evidence for dust aggregates

“…These observations indicate thick accumulations of a material that closely matches its surface properties. Similarly, GRS data are consistent with thick dust accumulations in Tharsis (down to the detection depth of about 50 cm) (Karunatillake et al, 2009). (2) A thick mantle precludes any locally-derived sand derived from breakup of the underlying basalt making it to the surface in sufficient quantities.…”

“…In addition to Tharsis, reticulate ridges have been identified in numerous locations across the planet, including Elysium (Bridges et al, 2007;Keszthelyi et al, 2008), draping deposits in Vallis Marineris (Keszthelyi et al, 2008), and in Daedalia Planum (Karunatillake et al, 2009). We have also recently found similar examples in Planum Boreum (Fig.…”

“…Analysis of elemental mass fractions in the upper ~ 50 cm derived from the Gamma Ray Spectrometer (GRS) investigation indicates that most of Tharsis is within an area relatively rich in chlorine and depleted in silicon and iron (Karunatillake et al, 2009). Together with the HiRISE images indicating a mantle at least 4 m thick (Keszthelyi et al, 2008), this points to more than a significant coating of dust.…”

“…More detailed studies of thermal data for this region, as well as laboratory investigations of dust aggregates, are needed. (6) The reticulate bedforms and yardangs overlap GRS signatures rich in Cl and poor in Si and Fe, indicating a composition of dust with added salts to depths of ~50 cm (Karunatillake et al, 2009). Cohesive soils on Mars are rich in sulfur and chlorine (Clark et al, 1982;Rieder et al, 2004).…”

Mars: a small terrestrial planet

“…Systematic evolution of surface concentrations of K, Th, and Fe with time was noticed in global analyses of Gamma Ray Spectrometer data (Hahn et al 2007;Karunatillake et al 2009), but these studies fail to decipher the respective role of primary and secondary processes in explaining these variations. Baratoux et al (2011) revisited this dataset and have provided evidence that systematic variations with time on Si, Fe, and Th concentrations on volcanic provinces were compatible with globally evolving conditions of partial melting related to the cooling of the mantle and to the thickening of the lithosphere.…”