Observational evidence of crystalline iron oxides on Mars

Abstract

Visible to near‐IR (0.4–1.0 μm) spectral reflectance observations of Mars during the 1988 opposition were performed at Mauna Kea Observatory using a circular variable filter spectrometer at a spectral resolution R = λ/Δλ ≈ 80. On August 13 and 14 1988, UT, 41 regions 500–600 km in diameter were observed on Mars. The data have been reduced both to reflectance relative to solar analog (Mars/16 Cyg B) and to relative reflectance (spot/spot). The spectra show the strong near‐UV reflectance dropoff characteristic of Mars as well as absorptions at 0.62–0.72 μm and 0.81–0.94 μm both seen here clearly for the first time. These absorption features are interpreted as Fe3+ electronic transition bands that indicate the presence of crystalline ferric oxide or hydroxide minerals on the Martian surface. Comparison of these data with laboratory spectra obtained by other workers supports the conclusion that a single iron oxide phase, most likely hematite, could account for all of the observed spectral behavior of the Martian surface soils and airborne dust in the 0.4–1.0 μm region. This possibility must be reconciled with data from other possible spectral analogs and other wavelength regions as well as geochemical and mineral stability considerations to arrive at a more complete understanding of the role of ferric minerals in Martian surface mineralogy and weathering.

Results from the Mars Pathfinder Camera

“…This type has a high red/blue ratio and a moderate kink parameter (24), indicative of an oxidized ferric-rich soil (25) ( Table 2). Bright soil spectra lack the weak 800 to 900 nm absorption found in the planet-wide dust (26,27), yet a global dust origin for bright soil is consistent with the wide distribution of this material around the Pathfinder site. The action of the rover wheels exposed other materials under the disturbed soil indicating a shallow depth.…”

“…The action of the rover wheels exposed other materials under the disturbed soil indicating a shallow depth. For comparison telescopic spectra of the bright and dark martian regions are plotted as well as a palagonitic soil often used as a martian analog (26,27).…”

“…None of the soils yet analyzed at the landing site show unique evidence for the types of crystalline hematite and/or pyroxene absorption features detected by remote sensing observations of other places on the martian surface (27,28). The origin of the 930-nm absorption seen most prominently in the Lamb-like soil may be an iron oxyhydroxide phase, a magnetic iron oxide, or a mixture of low Ca pyroxene and iron oxide (25,29).…”

The role of carbonates in the evolution of early Martian oceans

“…However, the question of whether or not true terrestrial-type oceans once existed on Mars remains controversial (see Kargel and Strom, 1996, for recent review). The widespread presence of weathered surface rocks and soil (Huguenin, 1976;Sidorov and Zolotov, 1986;Burns, 1993;Romanek and others, 1994), as well as salts (Clark and Van Hart, 1981;Bell, McCord, and Owensby, 1990;Plumlee, Ridkey, and DeBRaal, 1992), support the presence of extensive surface waters over a fairly long period of time. Landforms resembling terrestrial glacial features are indicative that there were once glaciers requiring a hydrologic cycle on early Mars involving liquid water (Kargel and Strom, 1992).…”

Magnetic Properties Experiments on the Mars Pathfinder Lander: Preliminary Results

“…There is spectral evidence of ferric iron in the martian soil (10). The soil in general is not only oxidized but is also strongly oxidizing, as evidenced by the effect on organic nutrients to which the soil was exposed in the Viking biology experiments (11).…”