A Low T, High Rh, and Potentially Life-friendly Environment within the Martian Salt-rich Subsurface in Equatorial Regions

2049 for XXXXII Lunar and Planetary Science Conference (March, 2011), Houston, TX A LOW T, HIGH RH, AND POTENTIALLY LIFE-FRIENDLY ENVIRONMENT WITHIN THE MARTIAN SALT-RICH SUBSURFACE IN EQUATORIAL REGIONS. Alian Wang 1 , M. P. Zheng 2 , F. J. Kong 2 , Z. C. Ling 3 , W. G. Kong 3 , P. Sobron 1 , B. L. Jolliff 1 , 1 Dept. of Earth and Planetary Sciences and the McDonnell Center for the Space Sciences, Washington University in St. Louis, One Brookings Drive, St. Louis, MO, 63130, USA. 2 R&D Center of Saline Lakes and Epithermal Deposits, Chinese Academy of Geological Sciences, Beijing, 100037, China. 3 School of Space Sciences and Physics, Shandong University, Weihai, China. Observations on Mars ― temporal changes in the properties of subsurface hydrous sulfates. Salt-rich light-toned soils were excavated by the Spirit rover at 18 locations in Gusev crater. Beneath the basaltic surface soils at the Tyrone site, two layers of sulfate-rich soils were found: the upper layer was white in color and rich in Ca-sulfates, the lower layer was yellow in color and rich in Fe-sulfates. A set of seven systematic Pancam observations of Tyrone salty soil were made from sol 864 to sol 1062 after its first excavation on sol 784. The major change observed was a reduction of albedo of the yellowish salty soils at 673 nm and 753 nm [1]. Recent spectral analysis based on two welldefined ROIs (Region Of Interest) for Tyrone yellowish and whitish salty soils [2] further confirmed that a spectral slope reduction from 673 nm to 432 nm (Fig. 1) of Tyrone yellow Fe-sulfate-rich soil occurred after its exposure to current surface atmospheric conditions. The change of spectral shape is consistent with the dehydration of Fe-sulfates [2]. A temporal property change of the subsurface soils excavated from tens of cm depth indicates that those soils were originally NOT in equilibrium with the surface atmospheric conditions at Gusev, and that a different environment exists within the subsurface saltrich regolith [1, 2]. Terrestrial observations -sulfates with high degrees of hydration found in the subsurface of a hyperarid region on the Qinghai-Tibet (QT) Plateau. QT Plateau has the highest average elevation on Earth (~ 4500 m), with ~50-60% of atmospheric pressure (P) at sea-level, high levels of UV radiation, low average temperatures (Tave), and large diurnal (and seasonal) temperature swings (T >80C). In addition, the Himalaya mountain chain (average height >6100 m) at south of the QT Plateau largely blocks humid air from the Indian Ocean, and produces a hyperarid region, the Qaidam Basin (N32-35, E90-100, Aridity Index, AI = 0.04 0.01) at the north edge of the QT Plateau [3]. Climatically, the low P, T, large T, high aridity, and high UV radiation all make the Qaidam basin one of the most similar places on Earth to Mars. We conducted a field investigation at Da Langtan (DLT) playa in the Qaidam basin [4], with combined remote sensing (ASTER: Terra satellite) [5], in-situ sensing with a portable NIR spectrometer (WIR-2: 1.25-2.5 μm) [6], and laboratory analyses of collected samples from the field (ASD: 0.4 -2.5 μm, WIR-3: 1.14 4.76 nm, Laser Raman spectroscopy, and XRD). One of the preliminary results is the finding of Mg sulfates with high degrees of hydration (MgSO46H2O & MgSO45H2O) within the subsurface salt layers [Fig. 2, 3]. Notice that hexahydrite and pentahydrated Mg sulfates would dehydrate quickly at relative humidity (RH) ≤ 33% and 5°C ≤ T ≤ 25°C [7]. Thus finding these phases in the subsurface of a hyperarid region (AI < 0.01) indicates, analogously to Tyrone, the existence of a different environment within the subsurface salt-rich layer. Extrapolation from thermal modeling -low Tave & small T within the salt-rich subsurface. Thermal modeling of a two-layer regolith (low-thermal-inertia material on top of high-thermal-inertia material) suggests a distinct temperature profile in the subsurface