Seasonally active slipface avalanches in the north polar sand sea of Mars: Evidence for a wind-related origin

Geophysical Research Letters, in press, doi:10.1029/2012GL051329

Meter-scale MRO/HiRISE camera images of dune slipfaces in the north polar sand sea of Mars reveal the presence of deep alcoves above depositional fans. These features are apparently active under current climatic conditions, because they form between observations taken in subsequent Mars years. Recently, other workers have hypothesized that the alcoves form due to destabilization and mass-wasting during sublimation of CO2 frost in the spring. While there is evidence for springtime modification of these features, our analysis of early springtime images reveals that over 80% of the new alcoves are visible underneath the CO2 frost. Thus, we present an alternative hypothesis that formation of new alcoves and fans occurs prior to CO2 deposition. We propose that fans and alcoves form primarily by aeolian processes in the mid- to late summer, through a sequence of aeolian deposition on the slipface, over-steepening, failure, and dry granular flow. An aeolian origin is supported by the orientations of the alcoves, which are consistent with recent wind directions. Furthermore, morphologically similar but much smaller alcoves form on terrestrial dune slipfaces, and the size differences between the terrestrial and martian features may reflect cohesion in the near-subsurface of the martian features. The size and preservation of the largest alcoves on the martian slipfaces also support the presence of an indurated surface layer; thus, new alcoves might be sites of early spring CO2 sublimation and secondary mass-wasting because they act as a window to looser, less indurated materials that warm up more quickly in the spring.

Widespread weathered glass on the surface of Mars

Briony Horgan and Jim Bell, published in Geology, May 2010

Low albedo sediments cover >107 km2 in the northern lowlands of Mars, but the composition and origin of these widespread deposits have remained ambiguous despite many previous investigations. Here we use near-infrared spectra acquired by the Mars Express OMEGA (Observatoire pour la Minéralogie, l'Eau, les Glaces, et l'Activité) imaging spectrometer to show that these sediments exhibit spectral characteristics that are consistent with both high abundances of iron-bearing glass and silica-enriched leached rinds on glass. This interpretation is supported by observations of low-albedo soil grains with possible rinds at the Phoenix Mars Lander landing site in the northern lowlands. By comparison with the extensive glass-rich dune fields and sand sheets of Iceland, we propose an explosive volcanic origin for these glass-rich sediments. We also propose that the glassy remnant rinds on the sediments are the result of postdepositional alteration, as these rinds are commonly formed in arid terrestrial volcanic environments during water-limited, moderately acidic leaching. These weathered, glass-rich deposits in the northern lowlands are also colocated with the strongest concentrations of a major global compositional surface type previously identified in mid-infrared spectra, suggesting that they may be representative of global processes. Our results provide potential confirmation of models suggesting that explosive volcanism has been widespread on Mars, and also raise the possibilities that glass-rich volcaniclastics are a major source of eolian sand on Mars and that widespread surficial aqueous alteration has occurred under Amazonian climatic conditions.

Searching for Pedogenic Phyllosilicates in Ancient Soils on Mars

Presented at the 2011 AGU Fall Meeting

On Earth, vast deposits rich in phyllosilicates are commonly created during soil formation, or pedogenesis. When soils are preserved in the stratigraphic record as paleosols, they become valuable resources for terrestrial geologists because paleosol isotopes, mineralogy, and chemical weathering profiles can be used to reconstruct ancient surface environments and to provide quantitative constraints on regional paleo-climate. Thus, paleosol sequences developed in sedimentary settings can record millions of years of surface and climatic evolution. Ancient paleosols on Earth also have excellent organic and biosignature preservation potential, and therefore harbor some of the oldest known (2-3 Ga) non-marine organics, biosignatures, and fossils.

On Mars, pedogenesis in the ancient past may be responsible for some of the phyllosilicate-bearing units observed today, especially for regionally extensive deposits and those in clear sedimentary settings (e.g., Arabia Terra/Mawrth Vallis, Gale Crater, Noctis Labyrinthus). Many of these possibly pedogenic deposits exhibit compositional layering (e.g., interbedded kaolinites, smectites, and sulfates), which may have formed due to episodic sediment deposition under changing environmental conditions. Such deposits represent excellent targets for in situ investigation, as finding and characterizing paleosols on Mars would allow us to place constraints on the extent and duration of past surface and near-surface habitability, and may even provide preserved samples of ancient martian organics.

We are currently investigating a broad range of methods for identifying and characterizing paleosols on Mars from orbit and in situ with Mars Science Laboratory, based on analysis of phyllosilicate-rich (30-95 wt.%) Eocene-Oligocene paleosols in the Painted Hills of the John Day Fossil Beds National Monument in Eastern Oregon. These paleosols were formed under a wide range of environmental conditions, and include highly weathered soils rich in well-crystalline oxides and kaolinites, moderately weathered soils rich in smectites, and minimally weathered soils rich in poorly-crystalline allophanes and ferrihydrite.

Here we present (1) an overview of the climatic regimes that lead to the pedogenesis of specific phyllosilicate minerals, (2) the near and mid-infrared spectral properties and interpreted mineral assemblages of these terrestrial paleosols, and (3) an evaluation of a pedogenic origin for phyllosilicates at several sites on Mars, including those listed above. Preliminary results from near-infrared spectral analysis of our terrestrial paleosols indicate that paleo-environment can be constrained based on mineral assemblages interpreted from spectral properties, including phyllosilicate composition (constrains water availability), the presence of allophane and ferrihydrite (indicating a cool climate), and the strength of oxide absorptions (constrains soil maturity). Mineral assemblages can also be used to detect burial diagenesis by the presence of diagenetic minerals, including celadonite, illite, and hematite (in the presence of phyllosilicates indicating less mature soils). Our results also indicate that poorly crystalline minerals (allophane and ferrihydrite) can be spectrally dominant in these soils even after burial and diagenesis.

Compositional relationships between high latitude units and implications for the history of the north polar region

Presented at the Fifth International Conference on Mars Polar Science and Exploration, Fairbanks, AK, 09/2011

Planum Boreum, the north polar plateau, is composed of a series of sedimentary deposits. Several of the major questions surrounding these deposits regard their origin, modification history, and their interrelationships. Here we present new results on the composition of mafic units in the north polar region that address these questions. These units include the north polar sand sea, sourced from within Planum Boreum, the Cavi unit, an indurated ancient sand dune sea, and the north polar veneers, which drape Planum Boreum and appear to be sourced from the Planum Boreum 2 (PB2) unit. Here we present results from spectral and morphologic studies, which together show that the history of these deposits involves volcanic, glacial, and sedimentary processes.

Acid alteration of basalts, andesites, and anorthosites: Near-IR spectra and implications for martian soil formation

Presented by my fabulous co-author Paul Mann at the 42nd Lunar and Planetary Science Conference, March 2011.

Acidic and oxidizing conditions have probably persisted on Mars for much of the past several billion years [1,2]. These conditions can cause alteration of  mafic rocks and minerals, producing a variety of secondary mineral assemblages, some of which have been observed by surface and orbital investigations at Mars. As such, previous laboratory investigations of these alteration processes have focused on the production and spectral character of the secondary minerals [5,6]. In this study, we are investigating the effects of acid alteration on the abundances and spectral characteristics of the primary, mafic minerals. Because mafic minerals have different solubilities, they alter at different rates, so their  relative abundances in altered surfaces may  help constrain the alteration processes that have occurred.

Summary of the Second International Planetary Dunes Workshop: Planetary Analogs--Integrating Models, Remote Sensing, and Field Data, Alamosa, Colorado, USA, …

Lori K. Fenton, Mark A. Bishop, Mary C. Bourke, Charles S. Bristow, Rosalyn K. Hayward, Briony H. Horgan, Nicholas Lancaster, Timothy I. Michaels, Daniela Tirsch, Timothy N. Titus, Andrew Valdez (2010). Published in 'Aeolian Research'.

The Second International Planetary Dunes Workshop took place in Alamosa, Colorado, USA from May 18–21, 2010. The workshop brought together researchers from diverse backgrounds to foster discussion and collaboration regarding terrestrial and extra-terrestrial dunes and dune systems. Two and a half days were spent on five oral sessions and one poster session, a full-day field trip to Great Sand Dunes National Park, with a great deal of time purposefully left open for discussion. On the last day of the workshop, participants assembled a list of thirteen priorities for future research on planetary dune systems.

Ice and sulfate induration in the martian north polar sand sea

Presented at the 2nd Planetary Dunes Workshop, 05/2010

Saltation has been a major erosional and depositional force on the surface of Mars, but the dynamics and timescales that govern the movement of martian sand dunes are poorly understood. In particular, major insights are needed into the mechanisms that cause induration of sand dunes and how these mechanisms affect dune migration rates. Possible modes of induration include chemical (cementation by salts, ferricrete, etc.), physical (settling and compaction of sand and/or dust), and niveo-aeolian (cementation by pore or interbedded ice). This study aims to search for evdience of each of these processes and evaluate their relative influence by examining dunes within the north polar sand sea, which encircles and is sourced from within the north polar plateau (Planum Boreum) [4]. The north polar sand sea offers a unique opportunity to study all of the above processes in one location, as both ice and soluble sulfates are present in the dune fields.

Distribution of hydrated minerals in the north polar region of Mars

Journal of Geophysical Research - Planets, 2009

The previous discovery of extensive deposits of hydrated minerals in Olympia Planum in the north polar region of Mars by the Mars Express OMEGA instrument raises important questions about the origin and subsequent redistribution of these hydrated minerals. Here we present a new map of the distribution of hydrated minerals within the north polar region of Mars by applying both standard and new spectral analysis techniques to near-infrared spectral data from OMEGA. Our results are in agreement with the previous OMEGA observations but also show more extensive detections of hydrated minerals throughout the circumpolar plains, as well as new detections of hydrated minerals on the surface of Planum Boreum and within the polar troughs. We find that while the circumpolar plains hydration signatures appear to be correlated with the dark dunes of the north polar erg, hydration signatures in Planum Boreum instead appear to be correlated with the north polar veneers and their sources within the polar layered deposits. By applying laboratory-derived empirical models of the dependence of gypsum spectra on grain size and abundance, we provide approximate abundance estimates for the hydrated minerals we have identified in Observatoire pour la Mine´ ralogie, l’Eau, les Glaces et l’Activite´ (OMEGA) and Compact Reconnaissance Imaging Spectrometer (CRISM) data. We find that the presence of hydrated minerals throughout the north polar region suggests (1) a complex cycle of sediment exchange between the Olympia Planum dunes and the other polar units; (2) an earlier origin for the hydrated minerals than originally postulated; and (3) the occurrence of significant water activity in this region during the Amazonian.

A 100-GHz high-gain tilted corrugated nonbonded platelet antenna

A 31 pixel flared 100-GHz high-gain scalar corrugated nonbonded platelet antenna array