Comet Ikeya-Zhang rises for the NAM

A possible naked-eye comet that may have been important in early cometary theory is announced by D J Asher , M E Bailey , A Christou , J McFarland , M F Muir and P P Rafferty .
Early indications sugest that Comet C/2002 (Ikeya-Zhang), discovered on 1 February 2002, may brighten to naked-eye visibility in late March 2002. It has also been suggested that it may be identical to one of the brighter comets of the 16th or 17th centuries, namely C/1532 R1 or C/1661 C1. The first of these, observed for more than 100 days towards the end of 1532, played an important role in the development of cometary theory. The second, although identified by Halley as having an orbit similar to that of the comet C/1532 R1, was not seen on its predicted return in 1788/1789 and so was presumably unrelated. Here we present long-term orbital integrations of C/2002 C1 which suggest that it orginated from the Oort cloud, and will be ejected again, within ˜0.3 Myr. There is a chance of 10–20% that it will end its life by falling into the Sun during a Halley-type phase of cometary evolution. The discovery of Ikeya-Zhang so closeto perigee by two amateur astonomers highlights the need for surveys covering both hemispheres to discover long-period and intermediate-period comets on Earth-crossing orbits.     

西藏日喀则地区德村-昂仁蛇绿岩内基性岩的元素与Sr-Nd-Pb同位素地球化学及其揭示的特提斯地幔域特征

系统研究了西藏雅鲁藏布江蛇绿岩带中部日喀则地区德村、吉丁和昂仁蛇绿岩中基性岩石的元素与 Sr-Nd-Pb 同位素地球化学特征。这些基性岩石,包括玄武岩、辉长岩和辉绿岩,属于低钾拉斑玄武岩系列,球粒陨石标准化稀土元素分配模式为轻稀土元素亏损的 N-MORB 型,(La/Yh)_N=0.31～0.65(除样品 DC993为1.17)。在原始地幔标准化微量元素图上,亏损高度不相容元素,与 N-MORB 配分模式一致。相对于 Th,无 Nb、Ta的亏损,显示样品不是产于 SSZ 环境。经构造环境图解判别,样品落入了 N-MORB 区域内;这些元素成分特征表明样品具有洋中脊环境或成熟的弧后盆地环境属性。Sr、Nd 和 Pb同位素组成特征表明特提斯地幔源区以 DM(亏损地幔)为主,同时存在少量 EMⅡ(富集地幔类型Ⅱ)、Sr,Nd 和 Pb 同位素组成特征还表明特提斯地幔域具有印度洋 MORB 型的 Sr-Nd-Pb 同位素组成特征。本文的结果进一步支持 Zhang et al.(2005)的研究结果,现今印度洋不仅在地理位置上占据了曾经是特提斯洋的大部分,而且它的地幔域还继承了曾经特提斯的地幔域的地球化学特征。     

内蒙古温都尔庙和巴彦敖包-交其尔蛇绿岩的元素与同位素地球化学：对古亚洲洋东部地幔域特征的限制

内蒙古中部发育的三条蛇绿岩带是华北板块和西伯利亚板块之间的缝合带。本文系统研究了其中的温都尔庙和巴彦敖包-交其尔两个蛇绿岩带中变质玄武岩的元素和 Sr、Nd、Pb 同位素地球化学。苏右旗温都尔庙碱性玄武岩为轻稀土富集型;岩石具有板内和大陆裂谷区玄武岩的特征,可能代表了600Ma 左右,温都尔庙地区开始发育的新洋盆。采自苏左旗的巴彦敖包-交其尔玄武岩分为两类,一类呈现轻稀土富集型,呈洋岛玄武岩特征;另一类具有明显的 Nb、Ta 负异常,显示大洋岛弧玄武岩特征,洋岛玄武岩的存在表明古亚洲洋曾经发育洋盆,大洋岛弧玄武岩的存在表明古亚洲洋内部有大洋岩石圈之间的俯冲。将本文的古亚洲洋洋岛玄武岩与中国西南地区的特提斯洋岛玄武岩进行系统的元素和同位素地球化学特征对比表明,古亚洲洋的洋岛玄武岩显示高 U/Pb(HU)和北大西洋和太平洋省的特征,而特提斯洋岛玄武岩属于印度洋省。这些说明古亚洲洋地幔域与特提斯地幔域是两个独立的构造域,它们代表了长期演化的两个不同的地幔地球化学域。     

Meteor observations in Japan: new implications for a Taurid meteoroid swarm

Observational evidence is sought that the long-term (10⁴ yr) action of a mean motion resonance with Jupiter can produce structure in a meteoroid stream, concentrating meteoroids in a dense swarm. More specifically, predictions tabulated by Asher & Clube of enhanced meteor and fireball activity from a Taurid Complex swarm in the 7:2 resonance are compared with observational data collected in Japan over several decades. The swarm model was proposed for reasons independent of the observations analysed here, and these newly considered data are shown to be consistent with it. This allows increased confidence in the Taurid swarm theory, and more generally could mean that resonant trapping is a dynamical mechanism affecting a significant amount of meteoroidal material in the inner Solar system.     

Fluvial processes and settlement in arid environments

The impact of fluvial geomorphic processes on settlement in deserts is tie d to two conflicting factors: the extreme rarity of geomorphic events on the one hand, and the violence of the geomorphic forces coupled with a minimal resistance to erosion on the other.The unique character of desert floods calls for a careful geomorphic evaluation in the siting of settlements and transportation facilities. On the beneficial sid e, the geomorphic processes involved enable, under some conditions, the local exploitation of floodwaters which percolate in the alluvium of the upper tributaries, as well as the utilization of the hydraulic geometry for estimating discharge characteristics.On a larger scale, human interference often disrupts the delicate quasi-equilbrium between erosion and sedimentation in deserts. Although our poor understanding of many aspects of the mechanism of response makes it difficult to separate the effects from those of climatic changes, enough information is available to document the detrimental effect of inconsiderate management on both the regional and local levels.     

The Leonid meteor storms of 1833 and 1966

The greatest Leonid meteor storms since the late eighteenth century are generally regarded as being those of 1833 and 1966. They were evidently due to dense meteoroid concentrations within the Leonid stream. At those times, the orbit of Comet 55P/Tempel–Tuttle was significantly nearer that of the Earth than at most perihelion returns, but still some tens of Earth radii away. Significantly reducing this miss distance can be critical for producing a storm. Evaluation of differential gravitational perturbations, comparing meteoroids with the comet, shows that, in 1833 and 1966 respectively, the Earth passed through meteoroid trails generated at the 1800 and 1899 returns.     

EURONEAR—Recovery, follow-up and discovery of NEAs and MBAs using large field 1–2 m telescopes

We report on the follow-up and recovery of 100 program NEAs, PHAs and VIs using the ESO/MPG 2.2 m, Swope 1 m and INT 2.5 m telescopes equipped with large field cameras. The 127 fields observed during 11 nights covered 29 square degrees. Using these data, we present the incidental survey work which includes 558 known MBAs and 628 unknown moving objects mostly consistent with MBAs from which 58 objects became official discoveries. We planned the runs using six criteria and four servers which focus mostly on faint and poorly observed objects in need of confirmation, follow-up and recovery. We followed 62 faint NEAs within one month after discovery and we recovered 10 faint NEAs having big uncertainties at their second or later opposition. Using the INT we eliminated four PHA candidates and VIs. We observed in total 1286 moving objects and we reported more than 10,000 positions. All data were reduced by the members of our network in a team effort, and reported promptly to the MPC. The positions of the program NEAs were published in 27 MPC and MPEC references and used to improve their orbits. The O−C residuals for known MBAs and program NEAs are smallest for the ESO/MPG and Swope and about four times larger for the INT whose field is more distorted. For the astrometric reduction, the UCAC-2 catalog is recommended instead of USNO-B1. The incidental survey allowed us to study statistics of the MBA and NEA populations observable today with 1–2 m facilities. We calculate preliminary orbits for all unknown objects, classifying them as official discoveries, later identifications and unknown outstanding objects. The orbital elements a, e, i calculated by FIND_ORB software for the official discoveries and later identified objects are very similar with the published elements which take into account longer observational arcs; thus preliminary orbits were used in statistics for the whole unknown dataset. We present a basic model which can be used to distinguish between MBAs and potential NEAs in any sky survey. Based on three evaluation methods, most of our unknown objects are consistent with MBAs, while up to 16 unknown objects could represent NEO candidates and four represent our best NEO candidates. We assessed the observability of the unknown MBA and NEA populations using 1 and 2 m surveys. Employing a 1 m facility, one can observe today fewer unknown objects than known MBAs and very few new NEOs. Using a 2 m facility, a slightly larger number of unknown than known asteroids could be detected in the main belt. Between 0.1 and 0.8 new NEO candidates per square degree could be discovered using a 2 m telescope.