Mars' “White Rock” feature lacks evidence of an aqueous origin: Results from Mars Global Surveyor

Abstract

Abstract. The "White Rock" feature on Mars has long been viewed as a type example for a Martian playa largely because of its apparent high albedo along with its location in a topographic basin (a crater). Data from the Mars Global Surveyor Thermal Emission Spectrometer (TES) demonstrate that White Rock is not anomalously bright relative to other Martian bright regions, reducing the significance of its albedo and weakening the analogy to terrestrial playas. Its thermal inertia value indicates that it is not mantled by a layer of loose dust, nor is it bedrock. The thermal infrared spectrum of White Rock shows no obvious features of carbonates or sulfates and is, in fact, spectrally flat. Images from the Mars Orbiter Camera show that the White Rock massifs are consolidated enough to retain slopes and allow the passage of saltating grains over their surfaces. Material appears to be shed from the massifs and is concentrated at the crests of nearby bedforms. One explanation for these observations is that White Rock is an eroded accumulation of compacted or weakly cemented aeolian sediment. IntroductionOne of the more enigmatic Martian landforms discovered in Mariner 9 images [McCauley, 1974], the colloquially named "White Rock" is an ---12 x 15 km exposure of relatively bright material on the floor of the 90-km-diameter crater Pollack at ---8øS, 335øW. The apparent high albedo of this compact grouping of bright ridges and dark troughs has led to speculation about its origin through a loosely drawn comparison to terrestrial evaporite deposits, which commonly are visibly bright.

Multiple techniques for mineral identification on Mars:

“…The current orbital and landed missions are enabling correlation of both the VNIR and mid-IR regions making the creation of combined spectral datasets of Mars analogs more essential. Summaries of the spectroscopic properties and composition of Mars have combined both the VNIR and thermal-IR spectroscopic results available at the time (Soderblom, 1992;Roush et al, 1993;; however, available spectroscopic studies of analogue materials utilizing both spectral regions (e.g., Bishop and Murad, 1996;Bishop et al, , 1998aBishop et al, , 1998bBishop et al, , 1998cBishop et al, , 1999Bishop et al, , 2001Bishop et al, , 2002 and the global spectral data available for Mars (e.g., Bandfield et al, 2000;Christensen et al, 2000aChristensen et al, , 2000bChristensen et al, , 2001aChristensen et al, , 2001bRuff et al, 2001;Hamilton et al, 2002) have increased substantially since then. This current study includes XRD, DTA, and Raman spectra in addition to VNIR and mid-IR spectra, because these other instruments may be a component on an upcoming lander/rover mission to Mars.…”

Layered, massive and thin sediments on Mars: possible Late Noachian to Late Amazonian tephra?

“…Compositionally, Mars tends to be mostly basaltic and the Thermal Emission Spectrometer (TES) on board MGS has not indicated the presence of carbonates or evaporites (Christensen et al 1998;Bandfield et al 2000); a potential problem for the lacustrine hypothesis of origin. Even 'White Rock', another LMT outcrop and a famous suspected crater-fill evaporite at 7°S, 335 °, lacks spectral evidence for an aqueous origin (Ruff et al 2000). However, with the exception of SEDIMENTS Medusae Fossae Formation outcrops, which emit basaltic spectra, many plotted LMT outcrops appear to show weak to strong correlation with TES designated locations of moderate to high concentrations of andesite Fig.…”

Related Magma–Ice Interactions: Possible Origins of Chasmata, Chaos, and Surface Materials in Xanthe, Margaritifer, and Meridiani Terrae, Mars

“…However, TES has not shown carbonates or evaporites on Mars. Even "white rock," another famous suspected crater-fill evaporite, lacks spectral evidence for an aqueous origin (Ruff et al 2000).…”