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211.
Lucy A. Mcfadden Dennis D. Wellnitz Matthew Schnaubelt Michael J. Gaffey J. F. Bell Noam Izenberg Scott Murchie Clark R. Chapman 《Meteoritics & planetary science》2001,36(12):1711-1726
Abstract— High signal‐to‐noise near‐infrared spectrometer (NIS) spectra acquired during the low phase flyby of the near‐Earth asteroid rendezvous (NEAR) mission to 433 Eros are analyzed to determine mineral chemistry and proportions of mafic silicates across the asteroid's surface at 2.68 × 5.50 km spatial resolution. Spectral band parameters are derived, and compared with those of laboratory samples of known mineral composition, grain size distribution and terrestrial, meteoritic and lunar pyroxene spectral properties. The NIS derived band parameters are consistent with ordinary chondrite meteorites. We invoke the presence of a clinopyroxene component in the spectra, which is consistent with ordinary chondrite mineralogy and/or some degree of partial melting of ordinary chondritic material. Spectra measured across the surface of Eros can reveal small but real spectral variations. Most relative spectra are uniform to within 1–2%. Some areas suggest compositional variations of a few percent. Spectral slope variations of a few percent are seen indicating a non‐uniform distribution of materials affecting the slope parameter but with no resolved absorption bands. We find no correlation of slope with viewing geometry or compositional variation. The band parameter values do not consistently indicate a specific ordinary chondrite class but Eros is definitely undifferentiated with possible compositional variations of no more than 1–2%. 相似文献
212.
G. A. Chapman 《Solar physics》1972,24(2):288-300
Spectroheliograms, having a resolution approaching 2, have been obtained which show He-D3 in absorption against the disk. The He-D3 features are compared with the distribution of magnetic fields and with H structures. The brightest regions in H usually show the strongest D3 absorption. Most H dark filaments show some D3 absorption, but the degree of correlation varies from filament to filament. The correlation between BII and He-D3 absorption is rather poor and the He features are much more diffuse than the photospheric magnetic field. 相似文献
213.
Sean C. Solomon Ralph L. McNutt Jr. Robert E. Gold Mario H. Acua Daniel N. Baker William V. Boynton Clark R. Chapman Andrew F. Cheng George Gloeckler James W. Head III Stamatios M. Krimigis William E. McClintock Scott L. Murchie Stanton J. Peale Roger J. Phillips Mark S. Robinson James A. Slavin David E. Smith Robert G. Strom Jacob I. Trombka Maria T. Zuber 《Planetary and Space Science》2001,49(14-15)
Mercury holds answers to several critical questions regarding the formation and evolution of the terrestrial planets. These questions include the origin of Mercury's anomalously high ratio of metal to silicate and its implications for planetary accretion processes, the nature of Mercury's geological evolution and interior cooling history, the mechanism of global magnetic field generation, the state of Mercury's core, and the processes controlling volatile species in Mercury's polar deposits, exosphere, and magnetosphere. The MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) mission has been designed to fly by and orbit Mercury to address all of these key questions. After launch by a Delta 2925H-9.5, two flybys of Venus, and two flybys of Mercury, orbit insertion is accomplished at the third Mercury encounter. The instrument payload includes a dual imaging system for wide and narrow fields-of-view, monochrome and color imaging, and stereo; X-ray and combined gamma-ray and neutron spectrometers for surface chemical mapping; a magnetometer; a laser altimeter; a combined ultraviolet–visible and visible-near-infrared spectrometer to survey both exospheric species and surface mineralogy; and an energetic particle and plasma spectrometer to sample charged species in the magnetosphere. During the flybys of Mercury, regions unexplored by Mariner 10 will be seen for the first time, and new data will be gathered on Mercury's exosphere, magnetosphere, and surface composition. During the orbital phase of the mission, one Earth year in duration, MESSENGER will complete global mapping and the detailed characterization of the exosphere, magnetosphere, surface, and interior. 相似文献
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215.
Robert D. Chapman 《Solar physics》1981,71(1):151-159
Spectroheliograms in high temperature ions such as Fe XV show the existence of both filaments that are brighter than the ambient corona and filaments that are darker than the ambient corona. We describe the relationship of the filaments to photospheric magnetograms, and discuss a possible physical mechanism to explain the differences. 相似文献
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218.
We model total solar irradiance (TSI) using photometric irradiance indices from the San Fernando Observatory (SFO), and compare our model with measurements compiled from different space-based radiometers. Space-based measurements of TSI have been obtained recently from ACRIM-3 on board the ACRIMSAT. These data have been combined with other data sets to create an ACRIM-based composite. From VIRGO on board the Solar and Heliospheric Observatory (SOHO) spacecraft two different TSI composites have been developed. The VIRGO irradiance data have been combined by the Davos group to create a composite often referred to as PMOD (Physikalisch-Meteorologisches Observatorium Davos). Also using data from VIRGO, the Royal Meteorological Institute of Belgium (RMIB) has created a separate composite TSI referred to here as the RMIB composite. We also report on comparisons with TSI data from the Total Irradiance Monitor (TIM) experiment on board the Solar Radiation and Climate Experiment (SORCE) spacecraft. The SFO model correlates well with all four experiments during the seven-year SORCE interval. For this interval, the squared correlation coefficient R 2 was 0.949 for SORCE, 0.887 for ACRIM, 0.922 for PMOD, and 0.924 for RMIB. Long-term differences between the PMOD, ACRIM, and RMIB composites become apparent when we examine a 21.5-year interval. We demonstrate that ground-based photometry, by accurately removing TSI variations caused by solar activity, is useful for understanding the differences that exist between TSI measurements from different spacecraft experiments. 相似文献
219.
The economy of Western Australia has long been characterized by a heavy dependence on extractive industries. The past decade, however, has seen the mining industry expand very rapidly, with significant implications for the small towns that support the sector. In this article, we consider the socio-economic performance of these towns through an assessment of unemployment, welfare dependence and incomes. In contrast to many other studies of resource boomtowns that typically focus on a single locality or time period, in this study we focus explicitly on spatial and temporal variability. We examine the ways in which place-specific characteristics—the commodity produced, local economic diversity and basic demographic features of a town—interact and have contributed to change in socio-economic well-being of mining communities across Western Australia over a 10-year period. 相似文献
220.
内蒙古苏尼特右旗晚石炭世本巴图组火山岩地球化学特征及构造意义 总被引:10,自引:0,他引:10
苏尼特右旗地区本巴图组火山岩主要由玄武安山岩及安山岩组成,含少量英安岩。安山岩的锆石U--Pb 年龄为300. 9 ± 1. 6 Ma。火山岩的化学成分总体具有拉斑系列的低钾、相对富铁的特征,微量元素组成与圣基茨岛弧火山岩十分相似,以轻重稀土的弱分馏、富集不相容元素、相对亏损高场强元素为特征。本巴图组火山岩具Eu 的负异常和贫Sr 特征,指示岩浆演化过程中经历过以斜长石为主的分离结晶作用,这一作用也导致了岩石贫铝、富钠。本巴图组火山岩初始岩浆起源于俯冲地幔楔的部分熔融,其形成与古亚洲洋板块的俯冲作用有关。 相似文献