Asteroid (101955) 1999 RQ36: Spectroscopy from 0.4 to 2.4 μm and meteorite analogs     

Beth Ellen Clark  Richard P. Binzel  Ellen S. Howell  Edward A. Cloutis  Maureen Ockert-Bell  Phil Christensen  Maria Antonietta Barucci  Francesca DeMeo  Dante S. Lauretta  Harold Connolly Jr.  Alicia Soderberg  Carl Hergenrother  Lucy Lim  Josh Emery  Michael Mueller 《Icarus》2011,216(2):462-475

We present reflectance spectra from 0.4 to 2.4 μm of Asteroid (101955) 1999 RQ36, the target of the OSIRIS-REx spacecraft mission. The visible spectral data were obtained at the McDonald Observatory 2.1-m telescope with the ES2 spectrograph. The infrared spectral data were obtained at the NASA Infrared Telescope Facility using the SpeX instrument. The average visible spectrum is combined with the average near-infrared wavelength spectrum to form a composite spectrum. We use three methods to constrain the compositional information in the composite spectrum of Asteroid (101955) 1999 RQ36 (hereafter RQ36). First, we perform a least-squares search for meteorite spectral analogs using 15,000 spectra from the RELAB database. Three most likely meteorite analogs are proposed based on the least-squares search. Next, six spectral parameters are measured for RQ36 and their values are compared with the ranges in parameter values of the carbonaceous chondrite meteorite classes. A most likely meteorite analog group is proposed based on the depth of overlap in parameter values. The results of the least-squares search and the parametric comparisons point to CIs and/or CMs as the most likely meteorite analogs for RQ36, and COs and CHs as the least likely. RQ36 has a spectrally “blue” continuum slope that is also observed in carbonaceous chondrites containing magnetite. We speculate that RQ36 is composed of a “CM1”-like material. Finally, we compare RQ36 to other B-type asteroids measured by Clark et al. (Clark, B.E. et al. [2010]. J. Geophys. Res. 115, E06005). The results of this comparison are inconclusive. RQ36 is comparable to Themis spectral properties in terms of its albedo, visible spectrum, and near-infrared spectrum from 1.1 to 1.45 μm. However, RQ36 is more similar to Pallas in terms of its near-infrared spectrum from 1.6 to 2.3 μm. Thus it is possible that B-type asteroids form a spectral continuum and that RQ36 is a transitional object, spectrally intermediate between the two end-members. This is particularly interesting because Asteroid 24 Themis was recently discovered to have H₂O ice on the surface (Rivkin, A., Emery, J. [2010]. Nature 464, 1322–1323; Campins, H. et al. [2010a]. Nature 464, 1320–1321).  相似文献   

The dynamics of central Main Ethiopian Rift waters: Evidence from δD, δO and Sr/Sr ratios     

Tewodros Rango  Riccardo Petrini  Barbara Stenni  Gianluca Bianchini  Francesca Slejko  Luigi Beccaluva  Tenalem Ayenew 《Applied Geochemistry》2010,25(12):1860-1871

Water samples from cold and geothermal boreholes, hot springs, lakes and rivers were analyzed for δD, δ¹⁸O and ⁸⁷Sr/⁸⁶Sr compositions in order to investigate lake water–groundwater mixing processes, water–rock interactions, and to evaluate groundwater flow paths in the central Main Ethiopian Rift (MER) of the Ziway–Shala basin. Different ranges of isotopic values were recorded for different water types: hot springs show δ¹⁸O −3.36 to +3.69 and δD −15.85 to +24.23, deep Aluto-Langano geothermal wells show δ¹⁸O −4.65 to −1.24 and δD −12.39 to −9.31, groundwater wells show δ¹⁸O −3.99 to +5.14 and δD −19.69 to +32.27, whereas the lakes show δ¹⁸O and δD in the range +3.98 to +7.92 and +26.19 to +45.71, respectively. The intersection of the Local Meteoric Water Line (LMWL: δD = 7 δ¹⁸O + 11.2, R² = 0.94, n = 42) and the Local Evaporation Line (LEL: δD = 5.63δ¹⁸O + 8, n = 14, R² = 0.82) was used to estimate the average isotopic composition of recharge water into the basin (δD = −5.15 and δ¹⁸O = −2.34). These values are depleted if compared with the modern-day average precipitation, presumably indicating paleo-groundwater components recharged during previous humid climatic phases. The measured stable isotope values indicate that the geothermal wells, some of the hot springs and groundwater wells mainly consist of meteoric water. The Sr isotopic signatures in all waters are within the range of the Sr isotopic composition of the rift basalts and rhyolites. The variability of Sr isotopic data also pinpoints complex water–rock interaction and mixing processes in groundwater and surface water. The ⁸⁷Sr/⁸⁶Sr ratio ranges from 0.70445 to 0.70756 in the hot springs, from 0.70426 to 0.70537 in two deep geothermal wells, and from 0.70673 to 0.70721 in the rift lakes Ziway, Langano, Shala and Awasa. The radiogenic composition recorded by the lakes indicates that the input water was predominantly affected by progressive interaction with rhyolitic volcanics and lacustrine sediments.  相似文献   

Horashim East: a newly discovered Middle Palaeolithic site in central Israel     

Ella Assaf  Viviane Slon  Francesca Romagnoli 《第四纪科学杂志》2022,37(1):1-5

Horashim East is a newly discovered Middle Palaeolithic open-air occurrence in central Israel, revealed during a thematic prehistoric survey. Hundreds of lithic items were found, including an early-stage biface, Levallois cores and products. As only a few open-air settlements are known from the Middle Palaeolithic Levant, the discovery of Horashim East sheds new light on human land-use patterns during this period and reinforces the notion that central-eastern Israel was favourable for human settlement throughout the Palaeolithic.  相似文献