Searching for the source regions of martian meteorites using MGS TES: Integrating martian meteorites into the global distribution of igneous materials on Mars     

Victoria E. HAMILTON  Philip R. CHRISTENSEN  Harry Y. McSWEEN  Joshua L. BANDFIELD 《Meteoritics & planetary science》2003,38(6):871-885

Abstract— The objective of this study was to identify and map possible source regions for all 5 known martian meteorite lithologies (basalt, lherzolite, clinopyroxenite, orthopyroxenite, and dunite) using data from the Mars Global Surveyor Thermal Emission Spectrometer (MGS TES). We deconvolved the TES data set using laboratory spectra of 6 martian meteorites (Los Angeles, Zagami, ALH A77005, Nakhla, ALH 84001, and Chassigny) as end members, along with atmospheric and surface spectra previously derived from TES data. Global maps (16 pixels/degree) of the distribution of each meteorite end member show that meteorite‐like compositions are not present at or above TES detectability limits over most of the planet's dust‐free regions. However, we have confidently identified local‐scale (100s‐1000s km²) concentrations of olivine‐ and orthopyroxene‐bearing materials similar to ALH A77005, Chassigny, and ALH 84001 in Nili Fossae, in and near Ganges Chasma, in the Argyre and Hellas basin rims, and in Eos Chasma. Nakhla‐like materials are identified near the detection limit throughout the eastern Valles Marineris region and portions of Syrtis Major. Basaltic shergottites were not detected in any spatially coherent areas at the scale of this study. Martian meteorite‐like lithologies represent only a minor portion of the dust‐free surface and, thus, are not representative of the bulk composition of the ancient crust. Meteorite‐like spectral signatures identified above TES detectability limits in more spatially restricted areas (<tens of km) are targets of ongoing analysis.  相似文献   

FAST APPROXIMATE INVERSION OF MAGNETOTELLURIC(FAIMT) DATA FOR A HORIZONTALLY LAYERED EARTH WITH NEAR-SURFACE INHOMOGENEITIES     

孙传文 《中国海洋湖沼学报》1997,15(1):7-18

IwrRODUcrIONNearsurface2-Dand3-DinhomogeneousdistortionsinMTdatamakeitdimculttointerpretMTdataevenwhentheregionalorbasinstruCturescanbetreatalas1-dfornsionalnyohmann,l975,Weide1t,l975,Wannamakeretal.,l984,LaTormcaetal.,l986,Zhang,l987,TorresWhrdinetal.,l992).Inthelasttwentyyears,2-Dand3-DmodelinghavebeenaanmPlishedbyusingnumricalmethods.Afteranalyringthesefor-wardmodelingresultS,wenowdeariyunderstandthemaorphySica1meCanisrnsasultingfromthesedistortionsofnear6urfaceinhomogeneities(Pa…  相似文献   

Chronological and palaeomagnetic constraints on widespread welded ignimbrites of the Taupo volcanic zone,New Zealand     

Tasha M. Black  Philip A. R. Shane  John A. Westgate  Paul C. Froggatt 《Bulletin of Volcanology》1996,58(2-3):226-238

 Large volume (100–1000 km³), widespread rhyolitic ignimbrites are the main products of the Taupo volcanic zone (TVZ) of New Zealand, one of the most active silicic volcanic regions on Earth. Several factors have made correlation and the eruptive history of the ignimbrites difficult to resolve, including limited exposure and chronological data, broadly similar lithologies and the lack of stratigraphic successions visible in the field. We have used the isothermal plateau fission track (ITPFT) method on glass shards from the non-welded basal zones to obtain new eruption ages for the widespread units: Ongatiti (1.25±0.12 Ma), Whakamaru group (0.34±0.03 Ma), Matahina (0.34±0.02 Ma), Chimp (0.33±0.02 Ma), Kaingaroa (0.31±0.01 Ma) and Mamaku (0.23±0.01 Ma) ignimbrites. These glasses show little evidence of geochemical alteration and allow the units to be fingerprinted for correlation. The glass ages we have obtained for the late Quaternary units provide an independent check on chronological data obtained from phenocryst phases. The ITPFT method is a useful dating approach for sanidine-poor eruptives which limit the application of ⁴⁰Ar/³⁹Ar. Errors as limited as 10–30 ka can be obtained from the weighted mean of several age determinations. The thermoremanent magnetic (TRM) direction recorded in the units provides a means of correlation over a wide area of the TVZ, because each ignimbrite can be distinguished by its unique record of palaeosecular variation. These data indicate that the four separately mapped members of the Whakamaru group represent the same phase of activity, occurring within a period of 100 years. The TRM data indicate that the widespread Ahuroa ignimbrite erupted during an excursion in Earth's magnetic field, perhaps associated with the Cobb Mountain subchron (ca. 1.2 Ma). The youngest widespread welded unit, Mamaku ignimbrite (ca. 0.23 Ma), also erupted during an excursion and may represent a southern hemisphere record of the Pringle Falls geomagnetic episode found in the western United States. The palaeomagnetic and ITPFT data for the widespread late Quaternary ignimbrites suggest a major period of caldera formation at 0.34–0.30 Ma. This interval represents the eruption of multiple units from the Whakamaru caldera, followed by the formation of the Okataina and Reporoa calderas in rapid succession. Received: 20 November 1995 / Accepted: 8 May 1996  相似文献   

Constraints on Jupiters from observations of Galactic bulge microlensing events during 2000     

Yiannis Tsapras †  Keith Horne  Richard Carson  Javier Méndez Alvarez  Dan Batcheldor  Alister W. Graham  Philip A. James  Johan Knapen  Hannah Quaintrell  Ignacio Gonzalez Serrano  Peter Sorensen  Nick Wooder 《Monthly notices of the Royal Astronomical Society》2002,337(1):41-48

We present observations of eight Galactic bulge microlensing events taken with the 1.0-m Jacobus Kapteyn Telescope (JKT) on La Palma during 2000 June and July. The JKT observing schedule was optimized using a prioritizing algorithm to automatically update the target list. For most of these events we have sampled the light curves at times where no information was available from the OGLE alert team. We assume a point-source point-lens (PSPL) model and perform a maximum likelihood fit to both our data and the OGLE data to constrain the event parameters of the fit. We then refit the data assuming a binary lens and proceed to calculate the probability of detecting planets with mass ratio   q = 10⁻³  . We have seen no clear signatures of planetary deviations on any of the eight events and we quantify constraints on the presence of planetary companions to the lensing stars. For two well-observed events, 2000BUL31 and 2000BUL33, our detection probabilities peak at ∼30 and ∼20 per cent respectively for   q = 10⁻³  and   a ∼ R _E  for a  Δχ²  threshold value of 60.  相似文献   

The variability of accretion on to Schwarzschild black holes from turbulent magnetized discs   总被引：1，自引：0，他引：1  

Philip J. Armitage  Christopher S. Reynolds 《Monthly notices of the Royal Astronomical Society》2003,341(3):1041-1050

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Fluvial system response to Late Devensian (Weichselian) aridity,Baston, Lincolnshire,England     

Rebecca M. Briant  G. Russell Coope  Richard C. Preece  David H. Keen  Steve Boreham  Huw I. Griffiths  Mary B. Seddon  Philip L. Gibbard 《第四纪科学杂志》2004,19(5):479-495

Little is known about the impact of Late Devensian (Weichselian) aridity on lowland British landscapes, largely because they lack the widespread coversand deposits of the adjacent continent. The concentration of large interformational ice‐wedge casts in the upper part of many Devensian fluvial sequences suggests that fluvial activity may have decreased considerably during this time. The development of optically stimulated luminescence (OSL) dating enables this period of ice‐wedge cast formation to be constrained for the first time in eastern England, where a marked horizon of ice‐wedge casts is found between two distinctive dateable facies associations. Contrasts between this horizon and adjacent sediments show clear changes in environment and fluvial system behaviour in response to changing water supply, in line with palaeontological evidence. In addition to providing chronological control on the period of ice‐wedge formation, the study shows good agreement of the radiocarbon and OSL dating techniques during the Middle and Late Devensian, with direct comparison of these techniques beyond 15 000 yr for the first time in Britain. It is suggested that aridity during the Late Devensian forced a significant decrease in fluvial activity compared with preceding and following periods, initiating a system with low peak flows and widespread permafrost development. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

The seasonal behavior of water ice clouds in the Tharsis and Valles Marineris regions of Mars: Mars Orbiter Camera Observations     

Jennifer L. Benson  Boncho P. Bonev  Philip B. James  Bruce A. Cantor 《Icarus》2003,165(1):34-52

The Mars Global Surveyor Mars Orbiter Camera was used to obtain global maps of the martian surface with equatorial resolution of 7.5 km/pixel in two wavelength ranges: blue (400-450 nm) and red (575-625 nm). The maps used were acquired between March 15, 1999 (L_s=110°) and July 31, 2001 (L_s=205°), corresponding to approximately one and a quarter martian years. Using the global maps, cloud area (in km²) has been measured daily for water ice clouds topographically corresponding to Olympus Mons, Ascraeus Mons, Pavonis Mons, Arsia Mons, Alba Patera, the western Valles Marineris canyon system, and for other small surface features in the region. Seasonal trends in cloud activity have been established for the three Tharsis volcanoes, Olympus Mons, and Alba Patera. Olympus, Ascraeus, and Pavonis Mons show cloud activity from about L_s=0°-220° with a peak in cloud area near L_s=100°. One of our most interesting observational results is that Alba Patera shows a double peaked feature in the cloud area with peaks at L_s=60° and 140° and a minimum near L_s=100°. Arsia Mons shows nearly continuous cloud activity. The altitudes of several of these clouds have been determined from the locations of the visual cloud tops, and optical depths were measured for a number of them using the DISORT code of Stamnes et al. (1988, Appl. Opt. 27, 2502-2509). Several aspects of the observations (e.g., cloud heights, effects of increased dust on cloud activity) are similar to simulations in Richardson et al. (2002, J. Geophys. Res. 107, 5064). A search for short period variations in the cloud areas revealed only indirect evidence for the diurnal cloud variability in the afternoon hours; unambiguous evidence for other periodicities was not found.  相似文献   

Satellite searches at Pluto and Mars     

Philip D. Nicholson  Brett J. Gladman 《Icarus》2006,181(1):218-222

We report the results of searches for outer satellites of Pluto and Mars, carried out with the Hale 5-m telescope in 1999 and 2001, respectively. No new satellites were found down to limiting magnitudes of mR=25.0 at Pluto and mV∼22 at Mars, corresponding to diameters of 35 and 1 km, respectively, for an assumed geometric albedo of 0.07. A faint trans-neptunian object, 1999 LB₃₇, was discovered in the Pluto fields; given the depth of our survey, discovery of one such object in the background Kuiper belt is in reasonable agreement with expectations.  相似文献   

Saturn's dynamic D ring     

Matthew M. Hedman  Joseph A. Burns  Mark R. Showalter  Philip D. Nicholson  Matthew S. Tiscareno  Bonnie J. Buratti  Roger Clark 《Icarus》2007,188(1):89-107

The Cassini spacecraft has provided the first clear images of the D ring since the Voyager missions. These observations show that the structure of the D ring has undergone significant changes over the last 25 years. The brightest of the three ringlets seen in the Voyager images (named D72), has transformed from a narrow, <40-km wide ringlet to a much broader and more diffuse 250-km wide feature. In addition, its center of light has shifted inwards by over 200 km relative to other features in the D ring. Cassini also finds that the locations of other narrow features in the D ring and the structure of the diffuse material in the D ring differ from those measured by Voyager. Furthermore, Cassini has detected additional ringlets and structures in the D ring that were not observed by Voyager. These include a sheet of material just interior to the inner edge of the C ring that is only observable at phase angles below about 60°. New photometric and spectroscopic data from the ISS (Imaging Science Subsystem) and VIMS (Visual and Infrared Mapping Spectrometer) instruments onboard Cassini show the D ring contains a variety of different particle populations with typical particle sizes ranging from 1 to 100 microns. High-resolution images reveal fine-scale structures in the D ring that appear to be variable in time and/or longitude. Particularly interesting is a remarkably regular, periodic structure with a wavelength of ∼30 km extending between orbital radii of 73,200 and 74,000 km. A similar structure was previously observed in 1995 during the occultation of the star GSC5249-01240, at which time it had a wavelength of ∼60 km. We interpret this structure as a periodic vertical corrugation in the D ring produced by differential nodal regression of an initially inclined ring. We speculate that this structure may have formed in response to an impact with a comet or meteoroid in early 1984.  相似文献   

Projections of the advance in the start of the growing season during the 21st century based on CMIP5 simulations     

XIA Jiangjiang  YAN Zhongwei  JIA Gensuo  ZENG Heqing  Philip Douglas JONES  ZHOU Wen  ZHANG Anzhi 《大气科学进展》2015,32(6):831-838

It is well-known that global warming due to anthropogenic atmospheric greenhouse effects advanced the start of the vegetation growing season(SOS) across the globe during the 20 th century. Projections of further changes in the SOS for the 21 st century under certain emissions scenarios(Representative Concentration Pathways, RCPs) are useful for improving understanding of the consequences of global warming. In this study, we first evaluate a linear relationship between the SOS(defined using the normalized difference vegetation index) and the April temperature for most land areas of the Northern Hemisphere for 1982–2008. Based on this relationship and the ensemble projection of April temperature under RCPs from the latest state-of-the-art global coupled climate models, we show the possible changes in the SOS for most of the land areas of the Northern Hemisphere during the 21 st century. By around 2040–59, the SOS will have advanced by-4.7 days under RCP2.6,-8.4 days under RCP4.5, and-10.1 days under RCP8.5, relative to 1985–2004. By 2080–99, it will have advanced by-4.3 days under RCP2.6,-11.3 days under RCP4.5, and-21.6 days under RCP8.5. The geographic pattern of SOS advance is considerably dependent on that of the temperature sensitivity of the SOS. The larger the temperature sensitivity,the larger the date-shift-rate of the SOS.  相似文献