排序方式: 共有14条查询结果,搜索用时 15 毫秒
1.
Trombka JI Squyres SW Bruckner J Boynton WV Reedy RC McCoy TJ Gorenstein P Evans LG Arnold JR Starr RD Nittler LR Murphy ME Mikheeva I McNutt RL McClanahan TP McCartney E Goldsten JO Gold RE Floyd SR Clark PE Burbine TH Bhangoo JS Bailey SH Petaev M 《Science (New York, N.Y.)》2000,289(5487):2101-2105
We report major element composition ratios for regions of the asteroid 433 Eros imaged during two solar flares and quiet sun conditions during the period of May to July 2000. Low aluminum abundances for all regions argue against global differentiation of Eros. Magnesium/silicon, aluminum/silicon, calcium/silicon, and iron/silicon ratios are best interpreted as a relatively primitive, chondritic composition. Marked depletions in sulfur and possible aluminum and calcium depletions, relative to ordinary chondrites, may represent signatures of limited partial melting or impact volatilization. 相似文献
2.
Peplowski PN Evans LG Hauck SA McCoy TJ Boynton WV Gillis-Davis JJ Ebel DS Goldsten JO Hamara DK Lawrence DJ McNutt RL Nittler LR Solomon SC Rhodes EA Sprague AL Starr RD Stockstill-Cahill KR 《Science (New York, N.Y.)》2011,333(6051):1850-1852
The MESSENGER Gamma-Ray Spectrometer measured the average surface abundances of the radioactive elements potassium (K, 1150 ± 220 parts per million), thorium (Th, 220 ± 60 parts per billion), and uranium (U, 90 ± 20 parts per billion) in Mercury's northern hemisphere. The abundance of the moderately volatile element K, relative to Th and U, is inconsistent with physical models for the formation of Mercury requiring extreme heating of the planet or its precursor materials, and supports formation from volatile-containing material comparable to chondritic meteorites. Abundances of K, Th, and U indicate that internal heat production has declined substantially since Mercury's formation, consistent with widespread volcanism shortly after the end of late heavy bombardment 3.8 billion years ago and limited, isolated volcanic activity since. 相似文献
3.
Herd CD Blinova A Simkus DN Huang Y Tarozo R Alexander CM Gyngard F Nittler LR Cody GD Fogel ML Kebukawa Y Kilcoyne AL Hilts RW Slater GF Glavin DP Dworkin JP Callahan MP Elsila JE De Gregorio BT Stroud RM 《Science (New York, N.Y.)》2011,332(6035):1304-1307
The complex suite of organic materials in carbonaceous chondrite meteorites probably originally formed in the interstellar medium and/or the solar protoplanetary disk, but was subsequently modified in the meteorites' asteroidal parent bodies. The mechanisms of formation and modification are still very poorly understood. We carried out a systematic study of variations in the mineralogy, petrology, and soluble and insoluble organic matter in distinct fragments of the Tagish Lake meteorite. The variations correlate with indicators of parent body aqueous alteration. At least some molecules of prebiotic importance formed during the alteration. 相似文献
4.
Nittler LR 《Science (New York, N.Y.)》2004,303(5658):636-637
5.
Keller LP Bajt S Baratta GA Borg J Bradley JP Brownlee DE Busemann H Brucato JR Burchell M Colangeli L d'Hendecourt L Djouadi Z Ferrini G Flynn G Franchi IA Fries M Grady MM Graham GA Grossemy F Kearsley A Matrajt G Nakamura-Messenger K Mennella V Nittler L Palumbo ME Stadermann FJ Tsou P Rotundi A Sandford SA Snead C Steele A Wooden D Zolensky M 《Science (New York, N.Y.)》2006,314(5806):1728-1731
Infrared spectra of material captured from comet 81P/Wild 2 by the Stardust spacecraft reveal indigenous aliphatic hydrocarbons similar to those in interplanetary dust particles thought to be derived from comets, but with longer chain lengths than those observed in the diffuse interstellar medium. Similarly, the Stardust samples contain abundant amorphous silicates in addition to crystalline silicates such as olivine and pyroxene. The presence of crystalline silicates in Wild 2 is consistent with mixing of solar system and interstellar matter. No hydrous silicates or carbonate minerals were detected, which suggests a lack of aqueous processing of Wild 2 dust. 相似文献
6.
Sandford SA Aléon J Alexander CM Araki T Bajt S Baratta GA Borg J Bradley JP Brownlee DE Brucato JR Burchell MJ Busemann H Butterworth A Clemett SJ Cody G Colangeli L Cooper G D'Hendecourt L Djouadi Z Dworkin JP Ferrini G Fleckenstein H Flynn GJ Franchi IA Fries M Gilles MK Glavin DP Gounelle M Grossemy F Jacobsen C Keller LP Kilcoyne AL Leitner J Matrajt G Meibom A Mennella V Mostefaoui S Nittler LR Palumbo ME Papanastassiou DA Robert F Rotundi A Snead CJ Spencer MK Stadermann FJ Steele A 《Science (New York, N.Y.)》2006,314(5806):1720-1724
Organics found in comet 81P/Wild 2 samples show a heterogeneous and unequilibrated distribution in abundance and composition. Some organics are similar, but not identical, to those in interplanetary dust particles and carbonaceous meteorites. A class of aromatic-poor organic material is also present. The organics are rich in oxygen and nitrogen compared with meteoritic organics. Aromatic compounds are present, but the samples tend to be relatively poorer in aromatics than are meteorites and interplanetary dust particles. The presence of deuterium and nitrogen-15 excesses suggest that some organics have an interstellar/protostellar heritage. Although the variable extent of modification of these materials by impact capture is not yet fully constrained, a diverse suite of organic compounds is present and identifiable within the returned samples. 相似文献
7.
CM Alexander R Bowden ML Fogel KT Howard CD Herd LR Nittler 《Science (New York, N.Y.)》2012,337(6095):721-723
Determining the source(s) of hydrogen, carbon, and nitrogen accreted by Earth is important for understanding the origins of water and life and for constraining dynamical processes that operated during planet formation. Chondritic meteorites are asteroidal fragments that retain records of the first few million years of solar system history. The deuterium/hydrogen (D/H) values of water in carbonaceous chondrites are distinct from those in comets and Saturn's moon Enceladus, implying that they formed in a different region of the solar system, contrary to predictions of recent dynamical models. The D/H values of water in carbonaceous chondrites also argue against an influx of water ice from the outer solar system, which has been invoked to explain the nonsolar oxygen isotopic composition of the inner solar system. The bulk hydrogen and nitrogen isotopic compositions of CI chondrites suggest that they were the principal source of Earth's volatiles. 相似文献
8.
Slavin JA Acuña MH Anderson BJ Baker DN Benna M Gloeckler G Gold RE Ho GC Killen RM Korth H Krimigis SM McNutt RL Nittler LR Raines JM Schriver D Solomon SC Starr RD Trávnícek P Zurbuchen TH 《Science (New York, N.Y.)》2008,321(5885):85-89
Observations by MESSENGER show that Mercury's magnetosphere is immersed in a comet-like cloud of planetary ions. The most abundant, Na+, is broadly distributed but exhibits flux maxima in the magnetosheath, where the local plasma flow speed is high, and near the spacecraft's closest approach, where atmospheric density should peak. The magnetic field showed reconnection signatures in the form of flux transfer events, azimuthal rotations consistent with Kelvin-Helmholtz waves along the magnetopause, and extensive ultralow-frequency wave activity. Two outbound current sheet boundaries were observed, across which the magnetic field decreased in a manner suggestive of a double magnetopause. The separation of these current layers, comparable to the gyro-radius of a Na+ pickup ion entering the magnetosphere after being accelerated in the magnetosheath, may indicate a planetary ion boundary layer. 相似文献
9.
Head JW Chapman CR Strom RG Fassett CI Denevi BW Blewett DT Ernst CM Watters TR Solomon SC Murchie SL Prockter LM Chabot NL Gillis-Davis JJ Whitten JL Goudge TA Baker DM Hurwitz DM Ostrach LR Xiao Z Merline WJ Kerber L Dickson JL Oberst J Byrne PK Klimczak C Nittler LR 《Science (New York, N.Y.)》2011,333(6051):1853-1856
MESSENGER observations from Mercury orbit reveal that a large contiguous expanse of smooth plains covers much of Mercury's high northern latitudes and occupies more than 6% of the planet's surface area. These plains are smooth, embay other landforms, are distinct in color, show several flow features, and partially or completely bury impact craters, the sizes of which indicate plains thicknesses of more than 1 kilometer and multiple phases of emplacement. These characteristics, as well as associated features, interpreted to have formed by thermal erosion, indicate emplacement in a flood-basalt style, consistent with x-ray spectrometric data indicating surface compositions intermediate between those of basalts and komatiites. The plains formed after the Caloris impact basin, confirming that volcanism was a globally extensive process in Mercury's post-heavy bombardment era. 相似文献
10.
McKeegan KD Aléon J Bradley J Brownlee D Busemann H Butterworth A Chaussidon M Fallon S Floss C Gilmour J Gounelle M Graham G Guan Y Heck PR Hoppe P Hutcheon ID Huth J Ishii H Ito M Jacobsen SB Kearsley A Leshin LA Liu MC Lyon I Marhas K Marty B Matrajt G Meibom A Messenger S Mostefaoui S Mukhopadhyay S Nakamura-Messenger K Nittler L Palma R Pepin RO Papanastassiou DA Robert F Schlutter D Snead CJ Stadermann FJ Stroud R Tsou P Westphal A Young ED Ziegler K Zimmermann L Zinner E 《Science (New York, N.Y.)》2006,314(5806):1724-1728
Hydrogen, carbon, nitrogen, and oxygen isotopic compositions are heterogeneous among comet 81P/Wild 2 particle fragments; however, extreme isotopic anomalies are rare, indicating that the comet is not a pristine aggregate of presolar materials. Nonterrestrial nitrogen and neon isotope ratios suggest that indigenous organic matter and highly volatile materials were successfully collected. Except for a single (17)O-enriched circumstellar stardust grain, silicate and oxide minerals have oxygen isotopic compositions consistent with solar system origin. One refractory grain is (16)O-enriched, like refractory inclusions in meteorites, suggesting that Wild 2 contains material formed at high temperature in the inner solar system and transported to the Kuiper belt before comet accretion. 相似文献