Lujendra Ojha

Seasonal Flows on Warm Martian Slopes

Rare meter-scale slope features on Mars might be explained by transient flows of liquid salty water. Water probably flowed across ancient Mars, but whether it ever exists as a liquid on the surface today remains debatable. Recurring slope lineae (RSL) are narrow (0.5 to 5 meters), relatively dark markings on steep (25° to 40°) slopes; repeat images from the Mars Reconnaissance Orbiter High Resolution Imaging Science Experiment show them to appear and incrementally grow during warm seasons and fade in cold seasons. They extend downslope from bedrock outcrops, often associated with small channels, and hundreds of them form in some rare locations. RSL appear and lengthen in the late southern spring and summer from 48°S to 32°S latitudes favoring equator-facing slopes, which are times and places with peak surface temperatures from ~250 to 300 kelvin. Liquid brines near the surface might explain this activity, but the exact mechanism and source of water are not understood.

Sulfates hydrating bulk soil in the Martian low and middle latitudes

The evidence for sulfate-bearing strata, across Late-Noachian to Amazonian eons, suggests a central role for sulfates in acidity and salinity of Martian paleofluids and the planets habitability. However, details remain unclear owing to shallow sampling and the limited ability of visible/near-infrared spectroscopy to distinguish among some sulfates. Using chemical data from the Mars Odyssey gamma ray spectrometer, including the sulfur map of Mars, we confirm the possibility of hydrous sulfates acting as key hydrates throughout the southern midlatitudinal soil at decimeter depths. An H2O:S molar ratio between 2.4 and 4.0 for 80% of the midlatitudes is also consistent with hydrous sulfate phases, including the many Fe sulfates hydrated in this range or mixtures of Ca and Mg sulfates. Nevertheless, hydrous Fe sulfates could explain our observations in a simpler manner relative to Ca/Mg mixtures. Furthermore, phyllosilicates, zeolites, amorphous phases, and H2O(s) do not seem to be strong candidates to explain the H-S variations. Consequently, we speculate that sulfates, as the primary contributor of H2O in bulk soil, may influence modern aqueous processes including warm-season slope lineae in the southern hemisphere.

Geologic context of recurring slope lineae in Melas and Coprates Chasmata, Mars

One of the major Mars discoveries of recent years is the existence of recurring slope lineae (RSL), which suggests that liquid water occurs on or near the surface of Mars today. These dark and narrow features emerge from steep, rocky exposures and incrementally grow, fade, and reform on a seasonal basis and are detected in images from the High Resolution Imaging Science Experiment camera. RSL are known to occur at scattered midlatitude and equatorial sites with little spatial connection to one another. One major exception is the steep, low-albedo slopes of Melas and Coprates Chasmata, in Valles Marineris where RSL are detected among diverse geologic surfaces (e.g., bedrock and talus) and landforms (e.g., inselbergs and landslides). New images show topographic changes including sediment deposition on active RSL slopes. Midwall locations in Coprates and Melas appear to have more areally extensively abundant RSL and related fans as compared with other RSL sites found on Mars. Water budget estimates for regional RSL are on the order of 105 to 106 m3 of fluid, for depths of 10 to 100 mm, and suggest that a significant amount of near-surface water might be present. Many RSL are concentrated near local topographic highs, such as ridge crests or peaks, which is challenging to explain via groundwater or ice without a recharge mechanism. Collectively, results provide additional support for the notion that significant amounts of near-surface water can be found on Mars today and suggest that a widespread mechanism, possibly related to the atmosphere, is recharging RSL sources.

Seismicity and the strange rubbing boulders of the Atacama Desert, northern Chile

We found clusters of 0.5–8 t boulders worn to smoothness around their midsections in the Atacama Desert of northern Chile. We suggest that the boulder smoothing is the cumulative result of at least 1 m.y. of rubbing between boulders during earthquakes. 10Be exposure ages of boulder tops from these fields average ∼1.3 m.y., unsurprisingly old given the hyperaridity of the Atacama. During a visit to one major boulder site, we experienced an earthquake that rocked but did not tip the boulders, causing them to rub against each other for about a minute. This MW 5.2 earthquake was centered ∼100 km northeast of the site. In the seismically active Atacama, earthquakes of this energy or greater occur about once every four months, suggesting that the average boulder has undergone ∼40,000–70,000 h of abrasion over the past 1.3 m.y. This unusual evidence underscores the largely unrecognized role that seismicity probably plays in hillslope sediment transport in the nearly rainless Atacama Desert, and perhaps on other seismically active but now dry worlds like Mars.

The Medusae Fossae Formation as the single largest source of dust on Mars

Transport of fine-grained dust is one of the most widespread sedimentary processes occurring on Mars today. In the present climate, eolian abrasion and deflation of rocks are likely the most pervasive and active dust-forming mechanism. Martian dust is globally enriched in S and Cl and has a distinct mean S:Cl ratio. Here we identify a potential source region for Martian dust based on analysis of elemental abundance data. We show that a large sedimentary unit called the Medusae Fossae Formation (MFF) has the highest abundance of S and Cl, and provides the best chemical match to surface measurements of Martian dust. Based on volume estimates of the eroded materials from the MFF, along with the enrichment of elemental S and Cl, and overall geochemical similarity, we propose that long-term deflation of the MFF has significantly contributed to the global Martian dust reservoir.Martian dust is globally enriched in S and Cl and has a distinct mean S:Cl ratio. Here the authors identify that the largest potential source region for Martian dust based on analysis of elemental abundance data may be the Medusae Fossae Formation.

The association of hydrogen with sulfur on Mars across latitudes, longitudes, and compositional extremes

NASA/Jet Propulsion Lab; NASA Mars Data Analysis Program [NNX07AN96G, NNX10AQ23G]; MDAP grants [NNX12AG89G, NNX13AI98G]; LSUs College of Science and Geology and Geophysics

Seasonal Slumps in Juventae Chasma, Mars

Dark topographic slumps several meters wide, tens of meters in length and up to a meter in depth are observed on the slopes of Juventae Chasma (JC), Valles Marineris (VM), Mars. These slumps usually originate near the terminal points of recurring slope lineae (RSL). Near their initiation points, the slumps have topographic depressions due to the removal of materials; near their lowermost reaches, new materials are deposited in lobes. Over the course of three Mars years, ten active slumps have been observed in JC, all of which formed in or near the same season (areocentric longitude: Ls 0°–120°). Mars Color Imager (MARCI) observations show low-altitude atmospheric obscurations confined within the topography of the VM and JC in the seasons when the slumps form. In one instance, data from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) and MARCI show evidence of H2O ice in the atmospheric obscuration, likely due to the formation of a low-level afternoon cloud above a dust storm, or mixing of condensate clouds with a diffuse dust cloud. The presence of atmospheric obscurations with H2O ice near times when the slumps form is intriguing, but no direct evidence currently exists to support that they aid in slump formation. Further monitoring of this site will help establish if RSL and/or atmospheric events play a role in the creation of contemporary slumps.