A comparison of the ultraviolet to near-infrared spectral properties of Mercury and the Moon as observed by MESSENGER     

Gregory M. Holsclaw  William E. McClintock  Noam R. Izenberg  Ann L. Sprague 《Icarus》2010,209(1):179-194

Measurements of the disk-integrated reflectance spectrum of Mercury and the Moon have been obtained by the MESSENGER spacecraft. A comparison of spectra from the two bodies, spanning the wavelength range 220-1450 nm, shows that the absolute reflectance of Mercury is lower than that of the nearside waxing Moon at the same phase angle with a spectral slope that is less steep at visible and near-infrared wavelengths. We interpret these results and the lack of an absorption feature at a wavelength near 1000 nm as evidence for a Mercury surface composition that is low in ferrous iron within silicates but is higher in the globally averaged abundance of spectrally neutral opaque minerals than the Moon. Similar conclusions have been reached by recent investigations based on observations from both MESSENGER and Mariner 10. There is weak evidence for a phase-reddening effect in Mercury that is slightly larger in magnitude than for the lunar nearside. An apparent absorption in the middle-ultraviolet wavelength range of the Mercury spectrum detected from the first MESSENGER flyby of Mercury is found to persist in subsequent observations from the second flyby. The current model of space weathering on the Moon, which also presumably applies to Mercury, does not provide an explanation for the presence of this ultraviolet absorption.  相似文献   

Hydrated mineral stratigraphy of Ius Chasma, Valles Marineris     

Leah H. Roach  John F. Mustard  Ralph E. Milliken  Scott L. Murchie 《Icarus》2010,206(1):253-60

New high-resolution spectral and morphologic imaging of deposits on walls and floor of Ius Chasma extend previous geomorphic mapping, and permit a new interpretation of aqueous processes that occurred during the development of Valles Marineris. We identify hydrated mineralogy based on visible-near infrared (VNIR) absorptions. We map the extents of these units with CRISM spectral data as well as morphologies in CTX and HiRISE imagery. Three cross-sections across Ius Chasma illustrate the interpreted mineral stratigraphy. Multiple episodes formed and transported hydrated minerals within Ius Chasma. Polyhydrated sulfate and kieserite are found within a closed basin at the lowest elevations in the chasma. They may have been precipitates in a closed basin or diagenetically altered after deposition. Fluvial or aeolian processes then deposited layered Fe/Mg smectite and hydrated silicate on the chasma floor, postdating the sulfates. The smectite apparently was weathered out of Noachian-age wallrock and transported to the depositional sites. The overlying hydrated silicate is interpreted to be an acid-leached phyllosilicate transformed from the underlying smectite unit, or a smectite/jarosite mixture. The finely layered smectite and massive hydrated silicate units have an erosional unconformity between them, that marks a change in surface water chemistry. Landslides transported large blocks of wallrock, some altered to contain Fe/Mg smectite, to the chasma floor. After the last episode of normal faulting and subsequent landslides, opal was transported short distances into the chasma from a few m-thick light-toned layer near the top of the wallrock, by sapping channels in Louros Valles. Alternatively, the material was transported into the chasma and then altered to opal. The superposition of different types of hydrated minerals and the different fluvial morphologies of the units containing them indicate sequential, distinct aqueous environments, characterized by alkaline, then circum-neutral, and finally very acidic surface or groundwater chemistry.  相似文献   

An Estimate of Eros's Porosity and Implications for Internal Structure     

Sarah L. WilkisonMark S. Robinson  Peter C. ThomasJoseph Veverka  Timothy J. McCoyScott L. Murchie  Louise M. ProckterDonald K. Yeomans 《Icarus》2002,155(1):94-103

Earth-based spectral measurements and NEAR Shoemaker magnetometer, X-ray, and near-infrared spectrometer data are all consistent with Eros having a bulk composition and mineralogy similar to ordinary chondrite meteorites (OC). By comparing the bulk density of 433 Eros (2.67±0.03 g/cm³) with that of OCs (3.40 g/cm³), we estimate the total porosity of the asteroid to be 21-33%. Macro (or structural) porosity, best estimated to be ∼20%, is constrained to be between 6 and 33%. We conclude that Eros is a heavily fractured body, but we find no evidence that it was ever catastrophically disrupted and reaccumulated into a rubble pile.  相似文献   

Permeability changes in layered sediments: impact of particle release   总被引：8，自引：0，他引：8  

Blume T  Weisbrod N  Selker JS 《Ground water》2002,40(5):466-474

One of the mechanisms of sudden particle release from grain surfaces in natural porous media is a decrease in salt concentration of the permeating fluid to below the critical salt concentration. Particle release can cause a change in hydraulic conductivity of the matrix, either by washing out the fines and thus increasing the pore sizes or by the plugging of pore constrictions. The phenomenon of permeability changes as a result of particle detachment was investigated in a series of column experiments. Coarse and fine sediments from the Hanford Formation in southeast Washington were tested. Columns were subject to a pulse of highly saline solution (NaNO3) followed by a fresh water shock causing particle release. Outflow rates and changes in hydraulic head as well as electric conductivity and pH were monitored over time. No permeability decrease occurred within the coarse matrix alone. However, when a thin layer of fine sediment was embedded within the coarse material (mimicking field conditions at the Hanford site), permeability irreversibly decreased to 10% to 20% of the initial value. Evidence suggests that most of this permeability decrease was a result of particles detached within the fine layer and its subsequent clogging. An additional observation was a sudden increase in pH in the outflow solution, generated in situ during the fresh water shock. Because layered systems are common in natural settings, our results suggest that alteration between sodium solution and fresh water can lead to particle release and subsequently reduce the overall permeability of the matrix.  相似文献   

Application of Tracking Technologies to the Study of Pedestrian Spatial Behavior*     

Noam Shoval  Michal Isaacson 《The Professional geographer》2006,58(2):172-183

Research into human spatial behavior has tended to rely solely on evidence provided by the research subjects themselves. Subjects' accounts of where they were and for how long were logged and integrated into time‐space diaries. In the past few years, a number of studies have exploited advanced tracking technologies instead of the traditional diary technique, however these were mostly transport studies focusing on vehicular movement. This article explores the implementation of tracking technologies as a tool for gathering data on pedestrian spatial behavior. The article considers two of the principal tracking technologies available today: satellite navigation systems and land‐based navigation systems. The makeup and properties of each technology are detailed, and their potential as data‐gathering tools on pedestrian spatial behavior is evaluated.  相似文献   

Environmental impact of an orchard winter wash and early season pesticide applications on both a beneficial and a pest mite species in Bramley apple orchards     

A. G. S. Cuthbertson  A. K. Murchie 《International Journal of Environmental Science and Technology》2006,3(4):333-339

Apple orchards often receive winter-washes to help aid invertebrate pest control. These can have detrimental environmental consequences. The application of winter-wash increased Aculus schlechtendali numbers while a decrease in numbers of the beneficial mite Anystis baccarum was observed. The application of early season pesticide treatments produced mixed results in relation to A. schlechtendali. Pirimiphos-methyl had no apparent detrimental effect on A. baccarum, whereas pirimicarb and phosalone reduced A. baccarum populations. The potential to incorporate an orchard winter-wash and early-season pesticide applications within integrated pest management strategies is discussed.  相似文献   

The palaeoflood record of a hyperarid catchment,Nahal Zin,Negev Desert,Israel     

Noam Greenbaum  Asher P. Schick  Victor R. Baker 《地球表面变化过程与地形》2000,25(9):951-971

The palaeohydrology of Nahal Zin, a 1400 km² catchment in the hyperarid Negev Desert, is inferred from slackwater deposits and palaeostage indicators in a canyon near its lower end. The palaeoflood record, augmented by the instrumental and historical records of the last decade, includes 28 floods ranging from 200 to 1500 m³s⁻¹ over the last 2000 years. This helps to reanalyse the frequency of floods in this drainage system. The clusters of floods around 1000 years BP and again during the last 60 years are characterized by high flow magnitudes. Periods with many floods correspond well to periods with high Dead Sea levels and are probably relatively wet periods, while periods with few floods correspond well to low Dead Sea levels indicating a drier climate. Fluctuations in the frequency of floods are typical of periods of transition from one climate regime to another. Copyright © 2000 John Wiley & Sons, Ltd.  相似文献   

Rotation, planets, and the 'second parameter' of the horizontal branch     

Noam Soker  Amos Harpaz 《Monthly notices of the Royal Astronomical Society》2000,317(4):861-866

We analyse the angular momentum evolution from the red giant branch (RGB) to the horizontal branch (HB) and along the HB. Using rotation velocities for stars in the globular cluster M13, we find that the required angular momentum for the fast rotators is up to 1–3 orders of magnitude (depending on some assumptions) larger than that of the Sun. Planets of masses up to 5 times Jupiter's mass and up to an initial orbital separation of ~2 au are sufficient to spin-up the RGB progenitors of most of these fast rotators. Other stars have been spun-up by brown dwarfs or low-mass main-sequence stars. Our results show that the fast rotating HB stars have been probably spun-up by planets, brown dwarfs or low-mass main-sequence stars while they evolved on the RGB. We argue that the angular momentum considerations presented in this paper further support the 'planet second parameter' model. In this model, the 'second parameter' process, which determines the distribution of stars on the HB, is interaction with low-mass companions, in most cases with gas-giant planets, and in a minority of cases with brown dwarfs or low-mass main-sequence stars. The masses and initial orbital separations of the planets (or brown dwarfs or low-mass main-sequence stars) form a rich spectrum of different physical parameters, which manifests itself in the rich varieties of HB morphologies observed in the different globular clusters.  相似文献   

Dust formation above cool magnetic spots in evolved stars     

Noam Soker  Geoffrey C. Clayton 《Monthly notices of the Royal Astronomical Society》1999,307(4):993-1000

We examine the structure of cool magnetic spots in the photospheres of evolved stars, specifically asymptotic giant branch (AGB) stars and R Coronae Borealis (RCB) stars. We find that the photosphere of a cool magnetic spot will be above the surrounding photosphere of AGB stars, which is the opposite of the situation in the Sun . This results from the behaviour of the opacity, which increases with decreasing temperature, which again is the opposite of the behaviour of the opacity near the effective temperature of the Sun . We analyse the formation of dust above the cool magnetic spots, and suggest that the dust formation is facilitated by strong shocks, driven by stellar pulsations, which run through and around the spots. The presence of both the magnetic field and cooler temperatures makes dust formation easier as the shock passes above the spot. We review some observations supporting the proposed mechanism, and suggest further observations to check the model.  相似文献   

Imprints of the Jittering Jets Explosion Mechanism in the Morphology of the Supernova Remnant SNR 0540-69.3     

Noam Soker 《天文和天体物理学研究(英文版)》2022,(3):186-193

I identify a point-symmetric structure in recently published VLT/MUSE velocity maps of different elements in a plane along the line of sight at the center of th...  相似文献