Allan H. Treiman

A Habitable Fluvio-Lacustrine Environment at Yellowknife Bay, Gale Crater, Mars

The Curiosity rover discovered fine-grained sedimentary rocks, which are inferred to represent an ancient lake and preserve evidence of an environment that would have been suited to support a martian biosphere founded on chemolithoautotrophy. This aqueous environment was characterized by neutral pH, low salinity, and variable redox states of both iron and sulfur species. Carbon, hydrogen, oxygen, sulfur, nitrogen, and phosphorus were measured directly as key biogenic elements; by inference, phosphorus is assumed to have been available. The environment probably had a minimum duration of hundreds to tens of thousands of years. These results highlight the biological viability of fluvial-lacustrine environments in the post-Noachian history of Mars.

Mineralogy of a Mudstone at Yellowknife Bay, Gale Crater, Mars

Sedimentary rocks at Yellowknife Bay (Gale crater) on Mars include mudstone sampled by the Curiosity rover. The samples, John Klein and Cumberland, contain detrital basaltic minerals, calcium sulfates, iron oxide or hydroxides, iron sulfides, amorphous material, and trioctahedral smectites. The John Klein smectite has basal spacing of ~10 angstroms, indicating little interlayer hydration. The Cumberland smectite has basal spacing at both ~13.2 and ~10 angstroms. The larger spacing suggests a partially chloritized interlayer or interlayer magnesium or calcium facilitating H2O retention. Basaltic minerals in the mudstone are similar to those in nearby eolian deposits. However, the mudstone has far less Fe-forsterite, possibly lost with formation of smectite plus magnetite. Late Noachian/Early Hesperian or younger age indicates that clay mineral formation on Mars extended beyond Noachian time.

Curiosity at Gale Crater, Mars: Characterization and Analysis of the Rocknest Sand Shadow

The Rocknest aeolian deposit is similar to aeolian features analyzed by the Mars Exploration Rovers (MERs) Spirit and Opportunity. The fraction of sand <150 micrometers in size contains ~55% crystalline material consistent with a basaltic heritage and ~45% x-ray amorphous material. The amorphous component of Rocknest is iron-rich and silicon-poor and is the host of the volatiles (water, oxygen, sulfur dioxide, carbon dioxide, and chlorine) detected by the Sample Analysis at Mars instrument and of the fine-grained nanophase oxide component first described from basaltic soils analyzed by MERs. The similarity between soils and aeolian materials analyzed at Gusev Crater, Meridiani Planum, and Gale Crater implies locally sourced, globally similar basaltic materials or globally and regionally sourced basaltic components deposited locally at all three locations.

X-ray diffraction results from mars science laboratory: Mineralogy of rocknest at Gale crater

The Mars Science Laboratory rover Curiosity scooped samples of soil from the Rocknest aeolian bedform in Gale crater. Analysis of the soil with the Chemistry and Mineralogy (CheMin) x-ray diffraction (XRD) instrument revealed plagioclase (~An57), forsteritic olivine (~Fo62), augite, and pigeonite, with minor K-feldspar, magnetite, quartz, anhydrite, hematite, and ilmenite. The minor phases are present at, or near, detection limits. The soil also contains 27 ± 14 weight percent x-ray amorphous material, likely containing multiple Fe3+- and volatile-bearing phases, including possibly a substance resembling hisingerite. The crystalline component is similar to the normative mineralogy of certain basaltic rocks from Gusev crater on Mars and of martian basaltic meteorites. The amorphous component is similar to that found on Earth in places such as soils on the Mauna Kea volcano, Hawaii.

Recent hotspot volcanism on venus from VIRTIS emissivity data

Hotspots on Venus The surface of Venus shows clear signs of volcanism, but are there active volcanoes on Venus today? The answer to this question will bear on our understanding of the planets climate evolution and interior dynamics. Using surface thermal emissivity data returned by the Venus Express spacecraft, Smrekar et al. (p. 605, published online 8 April) looked at three hotspots on Venus. These places were identified by analogy with terrestrial hotspots like Hawaii, which are believed to overlie mantle plumes and to be the most likely sites for current volcanic activity. Lava flows at the three hotspots have anomalously high thermal emissions when compared with their surroundings. Low emissivity is generally interpreted as the result of surface alteration by the corrosive atmosphere of Venus. High emissivity implies that not much alteration took place and thus that the hotspots must represent recently active volcanoes younger than 2.5 million years. Satellite observations suggest that Venus is a geologically active planet. The questions of whether Venus is geologically active and how the planet has resurfaced over the past billion years have major implications for interior dynamics and climate change. Nine “hotspots”—areas analogous to Hawaii, with volcanism, broad topographic rises, and large positive gravity anomalies suggesting mantle plumes at depth—have been identified as possibly active. This study used variations in the thermal emissivity of the surface observed by the Visible and Infrared Thermal Imaging Spectrometer on the European Space Agency’s Venus Express spacecraft to identify compositional differences in lava flows at three hotspots. The anomalies are interpreted as a lack of surface weathering. We estimate the flows to be younger than 2.5 million years and probably much younger, about 250,000 years or less, indicating that Venus is actively resurfacing.

The SNC meteorites are from Mars

Abstract The 14 SNC meteorites are all igneous rocks, either basalts or basaltic cumulates. They are inferred to be from Mars, based on direct comparison with Martian materials and on consistency with inferences about Mars. Most telling is that the SNC meteorites contain traces of gas which is very similar in elemental and isotopic compositions to the modern Martian atmosphere as measured by Viking landers on Mars and spectroscopy from Earth. The Martian atmosphere appears to have a unique composition in the solar system, so its presence in the SNCs is accepted as strong direct evidence that they formed on Mars. Independent of this link, the SNC meteorites must be from a planet with a significant atmosphere because they contain several abundant gas components, one of which carries large isotopic fractionations characteristic of atmospheric processing. Further, the elemental compositions and oxidation state of the SNC meteorites are consistent with data from in situ analyses of Martian soils and rocks, and are quite distinct from compositions of other meteorites, rocks from the Earth, and rocks from the Moon. The range of formation ages for the SNC meteorites, 4.5– 0.18 Ga , is consistent with the varied ages of the Martian surface (based on its cratering record) and inconsistent with surface ages on any other solar system body. The extreme chemical fractionations in the SNC meteorites suggest complex internal processes on a large planet, which is inconsistent with an asteroidal origin. Some SNCs were altered by aqueous solutions at Ga , consistent with the recent presence of liquid groundwater in Mars inferred independently from the geology of its surface. There seems little likelihood that the SNCs are not from Mars. If they were from another planetary body, it would have to be substantially identical to Mars as it now is understood.

Core formation in the Earth and Shergottite Parent Body (SPB): Chemical evidence from basalts☆

Constraints on processes of core formation in terrestrial planets may be inferred from the abundances of siderophile and chalcophile elements in their mantles. Of particular interest is a comparison of processes of core formation in the Earth and in the Shergottite Parent Body (SPB), a terrestrial planet tentatively inferred to be Mars. To this end, we (i) present new INAA and RNAA analyses of the non-Antarctic SNC meteorites, (ii) infer the composition of the SPB mantle from the compositions of the SNC meteorites, (iii) infer the composition of the Earths mantle from the compositions of terrestrial basalts, and (iv) deconvolve the effects of volatile depletion, core formation, and mineral/melt fractionation on the abundances of siderophile and chalcophile elements in the SPB and the Earth. Element abundances in the mantles of the SPB and the Earth are estimated from element/element correlations observed among basalt samples. In basalts from the SPB (the SNC meteorites), four groups of covariant elements are observed: highly incompatible, moderately incompatible, indifferent and compatible. From correlations within these groups, the SPB mantle is found to be depleted in volatile elements, and strongly depleted in siderophile and chalcophile elements. For the Earth, the element/element correlation method gives a mantle composition similar to previous estimates. Compared to the Earth, the SPB mantle is richer in moderately siderophile elements (e.g., W, P), consistent with its inferred higher oxidation state. Chalcophile elements in the SPB mantle are more depleted than in the Earths mantle, particularly when compared to estimates of the original abundances of volatile chalcophile elements in the two planets. In the SPB mantle, the NiCo ratio is nonchondritic, in contrast to the chondritic ratio in the Earths mantle. Abundances of siderophile and chalcophile elements in the SPB mantle may be modelled by equilibrium with solid metal and metallic sulfide liquid, with some metal and sulfide trapped in the mantle (i.e., homogeneous accretion and inefficient core formation). Neither this model nor a heterogeneous accretion model is satisfactory in explaining element abundances in the Earths mantle, particularly the abundances of Ni, Co, Mo, and W. Nevertheless it appears that core formation in the SPB and the Earth left quite different chemical signatures in their planetary mantles.

The Petrochemistry of Jake_M: A Martian Mugearite

“Jake_M,” the first rock analyzed by the Alpha Particle X-ray Spectrometer instrument on the Curiosity rover, differs substantially in chemical composition from other known martian igneous rocks: It is alkaline (>15% normative nepheline) and relatively fractionated. Jake_M is compositionally similar to terrestrial mugearites, a rock type typically found at ocean islands and continental rifts. By analogy with these comparable terrestrial rocks, Jake_M could have been produced by extensive fractional crystallization of a primary alkaline or transitional magma at elevated pressure, with or without elevated water contents. The discovery of Jake_M suggests that alkaline magmas may be more abundant on Mars than on Earth and that Curiosity could encounter even more fractionated alkaline rocks (for example, phonolites and trachytes).

A Reduced Organic Carbon Component in Martian Basalts

Abiotic Martian Organics Understanding the sources and the formation mechanisms of organic carbon compounds on Mars has implications for our understanding of the martian carbon cycle. Steele et al. (p. 212, published online 24 May) present measurements of organic material in 11 martian meteorites, including the Tissint meteorite, which fell in the Moroccan desert in July 2011. Ten of the meteorites contain complex hydrocarbons encased within igneous minerals. The results imply that the organics formed as the magma melt crystallized and are thus of abiotic origin. Analysis of 11 martian meteorites reveals complex hydrocarbons associated with magmatic minerals in 10 of them. The source and nature of carbon on Mars have been a subject of intense speculation. We report the results of confocal Raman imaging spectroscopy on 11 martian meteorites, spanning about 4.2 billion years of martian history. Ten of the meteorites contain abiotic macromolecular carbon (MMC) phases detected in association with small oxide grains included within high-temperature minerals. Polycyclic aromatic hydrocarbons were detected along with MMC phases in Dar al Gani 476. The association of organic carbon within magmatic minerals indicates that martian magmas favored precipitation of reduced carbon species during crystallization. The ubiquitous distribution of abiotic organic carbon in martian igneous rocks is important for understanding the martian carbon cycle and has implications for future missions to detect possible past martian life.

First use of an airborne thermal infrared hyperspectral scanner for compositional mapping

In May 1999, the airborne thermal infrared hyperspectral imaging system, Spatially Enhanced Broadband Array Spectrograph System (SEBASS), was flown over Mormon Mesa, NV, to provide the first test of such a system for geological mapping. Several types of carbonate deposits were identified using the 11.25-μm band. However, massive calcrete outcrops exhibited weak spectral contrast, which was confirmed by field and laboratory measurements. Because the weathered calcrete surface appeared relatively smooth in hand specimen, this weak spectral contrast was unexpected. Here we show that microscopic roughness not readily apparent to the eye has introduced both a cavity effect and volume scattering to reduce spectral contrast. The macroroughness of crevices and cobbles may also have a significant cavity effect. The diminished spectral contrast is important because it places higher signal-to-noise ratio (SNR) requirements for spectroscopic detection and identification. This effect should be factored into instrumentation planning and interpretations, especially interpretations without benefit of ground truth. SEBASS had the required high SNR and spectral resolution to allow us to demonstrate for the first time the ability of an airborne hyperspectral thermal infrared scanner to detect and identify spectrally subtle materials.