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Hematite spherules at Meridiani: results from MI, Mini-TES, and Pancam

Journal of Geophysical Research

By:
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DOI: 10.1029/2007JE003048

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Abstract

We report on observations of hematite-bearing spherules at Meridiani Planum made using the Microscopic Imager (MI), Mini-Thermal Emission Spectrometer (Mini-TES), and Panoramic Camera (Pancam) instruments on the Mars Exploration Rover Opportunity. Spherules were observed on soil surfaces and in outcrop rocks, both on undisturbed surfaces and in abraded surfaces ground using the Rock Abrasion Tool (RAT). Spherule size and shape change little along the 850 m eastward traverse from Eagle Crater to Endurance Crater, but spherules decrease and then slightly increase in size along the 6 km traverse from Endurance south to Victoria Crater. Local populations range from submillimeters to several millimeters in diameter. An additional small diameter (100 μm) size population is possible. An increase in irregular shapes is found near Victoria Crater. This, combined with the size decrease south of Endurance, suggests either a changing depositional environment, or variation in the duration and timing of diagenetic events. The dominant smaller size population observed early in the mission in aeolian areas and ripple crests is observed as the primary size population in abraded outcrop farther south. This suggests that successively younger beds are exposed at the surface along the southward traverse. Stratigraphically higher units removed by erosion could be recorded by the present surface lag deposit. Coordinated systematic observations are used to determine optical and infrared hematite indices of the surface soils in Pancam and Mini-TES. In spite of the systematic variation seen in MI, both Pancam and Mini-TES indices are highly variable based on the local surface, and neither show systematic trends south of Endurance. The lack of a 390 cm?1 feature in Mini-TES spectra suggests concentric or radial interior structure within the spherules at scales too fine for MI to observe. Mini-TES does not detect any silicate component in the spherules. A bound water component in soils or in exchange with the atmosphere is observed. These spherules have been previously interpreted as concretions formed within what were once water-saturated, diagenetically altered ?dirty evaporate? sandstone sediments. Our observations support this interpretation; however, no single terrestrial analog provides a model that can account for all attributes of the spherules on Mars.

Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
Hematite spherules at Meridiani: results from MI, Mini-TES, and Pancam
Series title:
Journal of Geophysical Research
DOI:
10.1029/2007JE003048
Volume
113
Year Published:
2008
Language:
English
Publisher:
American Geophysical Union
Publisher location:
Washington, D.C.
Contributing office(s):
Astrogeology Science Center
Description:
27 p.; E12S37
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
Larger Work Title:
Journal of Geophysical Research
Other Geospatial:
Mars;Meridiani Planum