A closely packed system of low-mass, low-density planets transiting Kepler-11

When an extrasolar planet passes in front of (transits) its star, its radius can be measured from the decrease in starlight and its orbital period from the time between transits. Multiple planets transiting the same star reveal much more: period ratios determine stability and dynamics, mutual gravitational interactions reflect planet masses and orbital shapes, and the fraction of transiting planets observed as multiples has implications for the planarity of planetary systems. But few stars have more than one known transiting planet, and none has more than three. Here we report Kepler spacecraft observations of a single Sun-like star, which we call Kepler-11, that reveal six transiting planets, five with orbital periods between 10 and 47?days and a sixth planet with a longer period. The five inner planets are among the smallest for which mass and size have both been measured, and these measurements imply substantial envelopes of light gases. The degree of coplanarity and proximity of the planetary orbits imply energy dissipation near the end of planet formation.     

羽毛状沙丘辨析

近年来,随着库姆塔格沙漠研究的深入,中国学者对羽毛状沙丘的争论愈来愈多。本文综合分析了国内外沙丘分类学中关于羽毛状沙丘的论述,确认羽毛状沙丘是复合线形沙垄的变型,其中沙垄主脊构成"羽柄",而叠加其上的次级沙丘脊歧出主沙丘脊,构成"羽毛"。对比分析世界其他沙漠与中国库姆塔格沙漠所谓羽毛状沙丘的形态学特征发现,库姆塔格沙漠所谓的羽毛状沙丘实际上是典型的赛夫沙丘,不应视为羽毛状沙丘。以往根据遥感影像确定的羽毛状沙丘的"羽毛"部分是由地表沉积物反照率对比形成的羽毛状图案,与垄间地的沙埂没有很好的对应关系。羽毛状沙丘是在比较复杂的风况和沙源供应不够充分的条件下形成的。因此本文认为以往关于库姆塔格沙漠羽毛状沙丘的不确切认识概念应予以纠正。     

Boundary-layer mantle flow under the Dead Sea transform fault inferred from seismic anisotropy

Lithospheric-scale transform faults play an important role in the dynamics of global plate motion. Near-surface deformation fields for such faults are relatively well documented by satellite geodesy, strain measurements and earthquake source studies, and deeper crustal structure has been imaged by seismic profiling. Relatively little is known, however, about deformation taking place in the subcrustal lithosphere--that is, the width and depth of the region associated with the deformation, the transition between deformed and undeformed lithosphere and the interaction between lithospheric and asthenospheric mantle flow at the plate boundary. Here we present evidence for a narrow, approximately 20-km-wide, subcrustal anisotropic zone of fault-parallel mineral alignment beneath the Dead Sea transform, obtained from an inversion of shear-wave splitting observations along a dense receiver profile. The geometry of this zone and the contrast between distinct anisotropic domains suggest subhorizontal mantle flow within a vertical boundary layer that extends through the entire lithosphere and accommodates the transform motion between the African and Arabian plates within this relatively narrow zone.