2010 Annual Research Report

Weitz is a Co-Investigator on the HiRISE camera that is now orbiting around Mars on the Mars Reconnaissance Orbiter spacecraft.HiRISE is taking images at the highest resolution of any camera around Mars, with ~26 cm/pixel spatial scales. Weitz is interested in the light-toned layered rocks on Mars and has been using the HiRISE images to explore the morphologies and origins for these deposits.She is also busy targeting the camera and prioritizing targets entered by anyone on sedimentary and layered deposits. 

A focus of Weitz’s research using HiRISE and CRISM (multispectral) data has been light-toned deposits (LTDs) that are found inside and around Valles Marineris. Weitz and her co-authors used data from the Mars Reconnaissance Orbiter (MRO) to analyze LTDs within two small troughs of Noctis Labyrinthus (Figure 1), the most western portion of Valles Marineris. Weitz and her team were able to infer the geologic history within these basin by combining stratigraphy derived from Digital Terrain Models (DTMs) with minerals identified in CRISM spectra. Minerals identified within the first trough include polyhydrated and monohydrated sulfates, kaolinite/bedeillite, hydrated silica, Fe-smectites, and a likely leached clay with a doublet absorption between 2.2-2.3 mm. In the second trough, minerals include opal/hydrated silica and/or Al- clays, sulfates, Fe/Mgsmectites,jarosite, kaolinite, leached clays, and mixtures of these minerals. Weitz and her team interpret the units to be coeval to trough formation, with some units initially emplaced in localized ancestral basins that subsequently became partially buried and then later exhumed by extension and erosion associated with formation of the current troughs, followed by additional deposition and/or alteration. These same units could underlie more of the Noctis Labyrinthus region than is observable today, but the original hydrologic and environmental conditions under which these units were emplaced remain unconstrained. The mineralogic diversity within each trough’s strata implies active hydrologic processes and/or changing chemical conditions, perhaps due to influxes of groundwater from nearby Tharsis volcanism.

Weitz is also currently analyzing hematite found within eastern Valles Marineris as part of a MDAP proposal with other PSI scientists, including Melissa Lane and Eldar Noe Dobrea. This work has shown that gray hematite is closely associated with light-toned units composed of kieserite but does not occur within these units (Figure 3). Instead, the hematite appears to erode from kieserite outcrops and then moves downslope where it collects along low-lying regions. These observations match those found at Meridiani Planum and elsewhere in Valles Marineris where hematite grains weather out from nearby sulfate exposures and then concentrate in a lag deposit. The hematite and monohydrated sulfate in Capri may have formed by diagenetic alteration of a sulfate-rich sedimentary deposit.

Another project funded through MDAP with PSI scientists Rebecca Williams and Eldar Noe Dobrea is to analyze and map the Melas Chasma basin on Mars (Figure 4). The Melas basin, located along the wallrock in southwestern Melas Chasma, contains layered beds in a postulated paleolake. In the western portion of the basin are extensive Hesperian-aged valley networks. Alluvial fans, folded beds, sulfate deposits, and depositional fans are also found within the basin. Together, these features define a complete erosional-to-depositional fluvial system. Using CRISM data, numerous hydrated units have been identified throughout the Melas basin. The units vary in absorption strengths and could represent mixtures of several phases. Morphologically, the hydrated units differ in lithology suggesting they are composed of distinct minerals and could have been emplaced by different processes. Thanks to help from Dan Berman, we have been able to produce Digital Terrain Models (DTMs) using HiRISE stereo pairs and overlay CRISM spectral information on the DTMS (Figure 5).By combining topographic information with mineralogy, we can infer the geologic history, particular changes in aqueous conditions with time.

Papers:

Weitz, C.M., R.E. Milliken, J.A. Grant, A.S. McEwen, R.M.E. Williams, J.L. Bishop, and B.J. Thompson. Mars Reconnaissance Orbiter observations of light-toned layered deposits and associated fluvial landforms on the plateaus adjacent to Valles Marineris. Icarus doi:10.1016/j.icarus.2009.04.017, 2010.

Weitz, C. M., et al. Visible and near-infrared multispectral analysis of geochemically measured rock fragments at the Opportunity landing site in Meridiani Planum, J. Geophys. Res., 115, E00F10,doi:10.1029/2010JE003660, 2010.

Fleischer, I., et al. (2010), Mineralogy and chemistry of cobbles at Meridiani Planum, Mars, investigated by the Mars Exploration Rover Opportunity, J. Geophys. Res., 115, E00F05, doi:10.1029/2010JE003621.

Abstracts:

Weitz, C.M., M. Lane, E. Noe Dobrea, L. Roach, and A. Knudson,Distribution and formation of crystalline gray hematite in eastern Valles Marineris. LPSC 41, Abstract 2264, 2010.

Weitz, C.M., J.L. Bishop, L. Roach, R.E. Milliken, and J.A. Rodriguez, Mineralogy and morphology of light-toned deposits in Noctis Labyrinthus. LPSC 41, Abstract 2240, 2010.

Farrand, W.H., J.R. Johnson, J.F. Bell, R.A. Yingst, and C.M Weitz, Distinguishing martian “erratics” from meteorites at Meridiani Planum using Pancam: Comparing Marquette Island to Meridiani Cobbles. LPSC 41, Abstract 1935, 2010.

Cabrol, N.A., E. A. Grin, K. E. Herkenhoff, C. M. Weitz, P. de Souza, and the Athena Science Team, Gusev soil analysis: Methods, inventory, and database. LPSC 41, Abstract 1182, 2010.

Johnson, J.R., K.E. Herkenhoff, J.F Bell III, W.H. Farrand, J. Ashley, C. Weitz, S.W. Squyres, Pancam visible/near-infrared spectra of large Fe-Ni meteorites at Meridiani Planum, Mars. LPSC 41, Abstract 1974, 2010.