RED HEMATITE AT MERIDIANI PLANUM, MARS AS OBSERVED BY THE MARS EXPLORATION ROVER OPPORTUNITY

The Mars Exploration Rover Opportunity was sent to Meridiani Planum based largely on MGS/TES spectroscopic evidence of a large surface exposure of coarse grained gray hematite. Remote multispectral imaging by the Hubble Space Telescope WFPC2 did not indicate the presence of red hematite in Meridiani Planum at scales of 10-20 km/pixel. Opportunity came to rest within a 20 m diameter crater dubbed Eagle. Early multispectral visible and near infrared observations by the rover’s Pancam of in situ rocks exposed on the inner wall of Eagle crater indicated a strong 535 nm absorption over some portions of the outcrop. These areas of high 535 nm band depth, tentatively assigned to red hematite, occur as patches on portions of the outcrop that present steeper faces and appear more resistant to erosion. In these areas, the band minimum of an expected 864 nm band can occur or be displaced to longer wavelengths, likely due to the additional presence of jarosite and/or ferrous iron bearing silicates. In situ examination of materials at Meridiani by the rover’s Moessbauer spectrometer has confirmed the presence of hematite as an abundant Fe-bearing mineral phase at Meridiani, occurring both in the outcrop and as a major component of the numerous spherules weathering from the outcrop and scattered on the plains. The rover’s mini-TES spectrometer has also confirmed the presence of gray hematite based on its thermal infrared spectral signature. The presence of red hematite, ostensibly produced as a by-product of abrasion of these spherules and disseminated gray hematite grains, was identified in Pancam spectra of the filings released by grinding into outcrop by the rover’s Rock Abrasion Tool (RAT). Strong 864 nm band depths in Pancam imagery is also associated with apparent natural abrasion of gray hematite concretions as they weather out of the Meridiani outcrop. The 864 nm band depth of spherules that are detached from the outcrop and resting on the plains tends to be less than that of in place spherules. These relations have also been observed outside of Eagle crater on the Meridiani plains and in and around the light toned rocks at the larger crater informally named Endurance. The VNIR coverage of the Pancam and mid-IR coverage of Mini-TES provide powerful tools to detect and distinguish between occurrences of red and gray hematite.