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1.
Abstract— The magnetometer experiment (MAG) onboard the Near‐Earth Asteroid Rendezvous (NEAR)‐Shoemaker spacecraft detected no global scale magnetization and established a maximum magnetization of 2.1 times 10?6 Am2 kg?1 for asteroid 433 Eros. This is in sharp contrast with the estimated magnetization of other S‐class asteroids (Gaspra, ?2.4 times 10?2 Am2 kg?1; Braille, ?2.8 times 10?2 Am2 kg?1) and is below published values for all types of ordinary chondrites. This includes the L/LL types considered to most closely match 433 Eros based on preliminary interpretations of NEAR remote geochemical experiments. The ordinary chondrite meteorite magnetization intensity data was reviewed in order to assess the reasonableness of an asteroid‐meteorite match based on magnetic property measurements. Natural remanent magnetization (NRM) intensities for the ordinary chondrite meteorites show at least a 2 order of magnitude range within each of the H, L, and LL groups, all well above the 2.1 times 10?6 Am2 kg?1 level for 433 Eros. The REM values (ratio of the NRM to the SIRM (saturation remanent magnetization)) range over 3 orders of magnitude for all chondrite groups indicating no clear relationship between NRM and the amount of magnetic material. Levels of magnetic noise in chondrite meteorites can be as much as 70% or more of the NRM. Consequently, published values of the NRM should be considered suspect unless careful evaluation of the noise sources is done. NASA Goddard SFC studies of per unit mass intensities in large (>10 000 g) and small (down to <1 g) samples from the same meteorite demonstrate magnetic intensity decreases as size increases. This would appear to be explained by demagnetization due to magnetic vector randomness at unknown scale sizes in the larger samples. This would then argue for some level of demagnetization of large objects such as an asteroid. The possibility that 433 Eros is an LL chondrite cannot be discounted.  相似文献   

2.
Magnetic measurements of meteorites suggest that small bodies (e.g. asteroids) in the Solar System have small but distinct magnetic fields produced by the bulk remanent magnetisation (NRM) of the body. Here we report calculations of magnetic fields of small bodies, assuming that they can be approximated as homogeneously magnetised spheres with dipole moments derived from NRM data on known meteorites. The magnetic fields are compared with the field of the asteroid 951 Gaspra measured by spacecraft Galileo in 1991 (Kivelson et al., 1993). The result of this comparison suggests that the field of Gaspra could be caused by an L-, H- or E-chondritic or a pallasite body. The spectral reflectance data on Gaspra suggest, however, that it is a basaltic achondrite. The problem can be resolved if Gaspra is a differentiated body, its surface material being closer to that of basaltic achondrites, and the bulk closer to ordinary chondrites or pallasites. We also present magnetic anomaly profiles along the surface of Mars such as would be measured with a magnetometer installed on a Rover-type vehicle by assuming that the main sources of the surface anomalies are the NRMs of the boulders on the Martian surface. The NRM values are taken from the data measured on SNC meteorites. The results suggest large oscillations in magnetic field intensity at the Martian surface.  相似文献   

3.
Magnetic measurements of meteorites suggest that small bodies (e.g. asteroids) in the Solar System have small but distinct magnetic fields produced by the bulk remanent magnetisation (NRM) of the body. Here we report calculations of magnetic fields of small bodies, assuming that they can be approximated as homogeneously magnetised spheres with dipole moments derived from NRM data on known meteorites. The magnetic fields are compared with the field of the asteroid 951 Gaspra measured by spacecraft Galileo in 1991 (Kivelson et al., 1993). The result of this comparison suggests that the field of Gaspra could be caused by an L-, H- or E-chondritic or a pallasite body. The spectral reflectance data on Gaspra suggest, however, that it is a basaltic achondrite. The problem can be resolved if Gaspra is a differentiated body, its surface material being closer to that of basaltic achondrites, and the bulk closer to ordinary chondrites or pallasites. We also present magnetic anomaly profiles along the surface of Mars such as would be measured with a magnetometer installed on a Rover-type vehicle by assuming that the main sources of the surface anomalies are the NRMs of the boulders on the Martian surface. The NRM values are taken from the data measured on SNC meteorites. The results suggest large oscillations in magnetic field intensity at the Martian surface.  相似文献   

4.
Abstract— Based on reflectance spectroscopy and chemical/mineralogical remote sensing methods, it is generally assumed that asteroids are parent bodies for most meteorites reaching the Earth. However, more detailed observations indicate that differences exist in composition between asteroids and meteorites resulting in difficulties when searching for meteorite‐asteroid match. We show that among other physical parameters the magnetic susceptibility of an asteroid can be determined remotely from the magnetic induction by solar wind using an orbiting spacecraft or directly using the AC coil on the lander, or it can be measured in samples returned to the laboratory. The shape corrected value of the true magnetic susceptibility of an asteroid can be compared to those of meteorites in the existing database, allowing closer match between asteroids and meteorites. The database of physical properties contains over 700 samples and was recently enlarged with measurements of meteorites in European museums using mobile laboratory facility.  相似文献   

5.
The average directions of natural remanent magnetization (NRM) of three texturally distinct layers (72215, 72255, and 72275) of a 2 m-sized breccia boulder were found to be the same, while the directions of their stable components of NRM were found to be widely divergent. One clast from 72275 yielded a stable NRM direction which was different from that of the matrix. Approximate paleointensity measurements showed that 72255 and 72275 could have obtained their stable remanence from an ancient magnetic field of the same magnitude. However, 72215 probably was magnetized by a magnetic field of a different intensity. We concluded that the coincident NRM directions owe their origin to a secondary imprint of less stable magnetization imparted during the assembly of the boulder at moderate temperatures (～ 450°C) on the South Massif. The stable directions, on the other hand, date from the last, higher-temperature (～ 770°C) magnetizing event experienced by the mineral and lithic components while they were part of the immature pre-Serenitatis regolith.  相似文献   

6.
Space weathering is now generally accepted to modify the optical and magnetic properties of airless planetary regoliths such as those on the Moon and Mercury. Under micrometeorite and ion bombardment, ferrous iron in such surfaces is reduced to metallic iron spheres, found in amorphous coatings on almost all exposed regolith grains. The size and number distribution of these particles and their location in the regolith all determine the nature and extent of the optical and magnetic changes. These parameters in turn reflect the formation mechanisms, temperatures, and durations involved in the evolution of the regolith. Studying them in situ is of intrinsic value to understanding the weathering process, and useful for determining the maturity of the regolith and providing supporting data for interpreting remotely sensed mineralogy. Fine-grained metallic iron has a number of properties that make it amenable to magnetic techniques, of which magnetic susceptibility is the simplest and most robust. The magnetic properties of the lunar regolith and laboratory regolith analogues are therefore reviewed and the theoretical basis for the frequency dependence of magnetic susceptibility presented. Proposed here is then an instrument concept using multi-frequency measurements of magnetic susceptibility to confirm the presence of fine-grained magnetic material and attempt to infer its quantity and size distribution. Such an instrument would be invaluable on a future mission to an asteroid, the Moon, Mercury or other airless rocky Solar System body.  相似文献   

7.
Abstract— Due to the effects of erosion, tectonism and burial, impact structures are often obscured or destroyed. Geophysical methods are increasingly being used in detecting the signatures of impact structures. While gravity lows associated with impact structures are well understood, associated magnetic anomaly lows are not. In this study, drill cores from three Canadian impact structures were analyzed for rock magnetic properties and mineralogy, in order to explain the magnetic anomaly lows associated with these structures. Samples from the drill cores were cut and measured for anisotropy of magnetic susceptibility (AMS) and natural remanent magnetization (NRM) parameters. Drill cores from the twin impact craters of the Clearwater structure exhibited different NRM characteristics, and samples from their respective drill cores were subject to demagnetization by alternating field and thermal techniques. The difference noted in their NRM characteristics was attributed to the acquisition of a viscous remanent magnetization (VRM) at depth in Clearwater East. At all three structures, both magnetic susceptibilities and remanent magnetizations are well below regional values in impact generated breccias, melt rocks, shocked crystalline rocks, and in postimpact sedimentary infill. The processes of brecciation, alteration, shock, and infill by nonmagnetic sediments contribute to the development of the magnetic lows. However, a significant contribution to the observed magnetic anomalies was found, by first-order forward modelling, to arise from basement rocks beneath the impact structures. This zone of reduced magnetization may be caused by the partial demagnetization of magnetite by the impact-induced transient stress wave traveling away from the point of impact.  相似文献   

8.
Abstract— Evolutionary processes in meteorites and magnetic fields in the early solar system, both spatial and localised in planetary bodies, can leave their imprint in meteorites through the natural remanent magnetization (NRM) and other magnetic properties they impart to them. In the present investigation the Estherville mesosiderite has been studied to enquire whether its magnetic properties can help to resolve any of the uncertainties associated with mesosiderite history and evolution, and to examine evidence for any magnetic fields to which it or its constituent fragments have been subjected. The Estherville sample as received is strongly magnetized, with an initial NRM intensity of 1.4 × 10?3 Am2 kg?1. The NRM of individual fragments broken from the main mass, when referred to common reference axes, is scattered in direction on a scale which ranges from ～ 1 cm down to ～ 1 mm. Alternating field and thermal demagnetization show a range of magnetic stability among the samples and also some secondary NRM, indicating a variety of magnetic histories. Thermomagnetic analyses of matrix and iron-nickel separates show that the dominant magnetic carriers are kamacite and tetrataenite. The non-coherent directions of NRM within the matrix imply the acquisition of an initial NRM by kamacite in the fragments prior to their final accumulation into the mesosiderite material, and the presence of an ambient magnetic field when the fragment material cooled after its formation. If the tetrataenite carrying the primary NRM was formed from the previously magnetized kamacite/taenite during slow cooling after later metamorphic heating, the maximum temperature during the latter event could not have been higher than ～700 °C or the kamacite would have been remagnetized uniformly or demagnetized, according to whether or nor there was an ambient magnetic field present. Susceptibility anisotropy observations indicate the acquisition of anisotropic properties occurred before final accumulation of the meteorite. Shock and flow processes were probably important in producing foliation and lineation respectively in the fragments resulting from brecciation, and there could also be a contribution from larger metal fragments and/or veins. The scattered NRM of the iron-nickel fragments also indicates magnetization prior to emplacement, therefore favouring introduction in the solid rather than the molten form.  相似文献   

9.
Abstract— We report on the effectiveness of using magnetic measurements in the search for meteorites on the Antarctic ice sheet, which is thus far the Earth's most productive terrain. Magnetic susceptibility measurements carried out with a pocket meter (SM30) during the 2003/04 PNRA meteorite collection expedition to northern Victoria Land (Antarctica) proved to be a rapid, sensitive, non‐destructive means for the in situ identification, pairing, and classification of meteorites. In blue ice fields characterized by the presence of moraines and glacial drifts (e.g., Miller Butte, Roberts Butte, and Frontier Mountain), magnetic susceptibility measurements allowed discrimination of meteorites from abundant terrestrial stones that look like meteorites thanks to the relatively high magnetic susceptibility of the former with respect to terrestrial rocks. Comparative measurements helped identify 16 paired fragments found at Johannessen Nunataks, thereby reducing unnecessary duplication of laboratory analyses and statistical bias. Following classifications schemes developed by us in this and previous works, magnetic susceptibility measurements also helped classify stony meteorites directly in the field, thereby providing a means for selecting samples with higher research priority. A magnetic gradiometer capable of detecting perturbations in the Earth's magnetic field induced by the presence of meteorites was an efficient tool for locating meteorites buried in snow along the downwind margin of the Frontier Mountain blue ice field. Based on these results, we believe that magnetic sensors should constitute an additional payload for robotic search for meteorites on the Antarctic ice sheet and, by extension, on the surface of Mars where meteorite accumulations are predicted by theoretical works. Lastly, magnetic susceptibility data was successfully used to crosscheck the later petrographic classification of the 123 recovered meteorites, allowing the detection of misclassified or peculiar specimens.  相似文献   

10.
We have examined the magnetic characteristics of representative ureilites, with a view to identify the magnetic effects of shock and to isolate a primary component of the natural remanent magnetization (NRM). As a group, the ureilites show remarkably uniform patterns of magnetic behavior, attesting to a common genesis and history. However, a clearly observed gradation in magnetic properties of the ureilites studied with shock level, parallels their classification based on petrologic and chemical fractionation shock-related trends.The ureilite meteorites possess a strong and directionally stable NRM. Laboratory thermal modelling of this presumably primordial NRM preserved in Goalpara and Kenna produced reliable paleointensity estimates of order 1 Oe, thus providing evidence for strong early, nebular magnetic fields. This paleofield strength is compatible with values obtained previously from carbonaceous chondrites and supports isotopic evidence for a contemporary origin of these two groups of meteorites in the same nebular region. The mechanism for recording nebular fields, manifestly different in carbonaceous chondrite vs. ureilite meteorites, is thus relatively unimportant: violent collisional shock in ureilites seems to have only partially altered an original magnetization, by preferential removal of its least stable portion.  相似文献   

11.
Abstract— Results of a detailed paleomagnetic and rock magnetic study of samples of the impact breccia sequence cored in the Yaxcopoil‐1 (Yax‐1) borehole between about 800 m and 896 m are presented. The Yax‐1 breccia sequence occurs from 794.63 m to 894.94 m and consists of redeposited melt‐rich, clast‐size sorted, fine‐grained suevites; melt‐rich, no clast‐size sorting, medium‐grained suevites; coarse suevitic melt agglomerates; coarse melt‐rich heterogeneous suevites; brecciated suevites; and coarse carbonate and silicate melt suevites. The low‐field susceptibility ranges from ?0.3 to 4018 times 10?6 SI, and the NRM intensity ranges from 0.02 mA/m up to 37510 mA/m. In general, the NRM intensity and magnetic susceptibility present wide ranges and are positively correlated, pointing to varying magnetic mineral contents and textures of the melt‐rich breccia sequence. The vectorial composition and magnetic stability of NRM were investigated by both stepwise alternating field and thermal demagnetization. In most cases, characteristic single component magnetizations are observed. Both upward and downward inclinations are present through the sequence, and we interpret the reverse magnetization as the primary component in the breccias. Both the clasts and matrix forming the breccia appear to have been subjected to a wide range of temperature/pressure conditions and show distinct rock magnetic properties. An extended interval of remanence acquisition and secondary partial or total remagnetization may explain the paleomagnetic results.  相似文献   

12.
two near-earth-asteroids associated with resonances with Jupiter are studied over a time span of 105 yrs. We found that asteroid (887) is temporary trapped in the 3:1 resonance; thus indicating that this resonance could be a source of short-lived NEAs. We also found that asteroid (3552) with a large eccentricity and a high inclination is wandering about the 1:1 resonant region.  相似文献   

13.
Abstract– The Lonar crater in Maharashtra state, India, has been completely excavated on the Deccan Traps basalt (approximately 65 Ma) at approximately 570 ± 47 ka by an oblique impact of a possible chondritic asteroid that struck the preimpact target from the east at an angle of approximately 30–45o to the horizon where the total duration of the shock event was approximately 1 s. It is shown by our early work that the distribution of ejecta and deformation of target rocks around the crater rim are symmetrical to the east–west plane of impact ( Misra et al. 2010 ). The present study shows that some of the rock magnetic properties of these shocked target basalts, e.g., low‐field anisotropy of magnetic susceptibility (AMS), natural remanent magnetization (NRM)/bulk susceptibility (χ), and high‐coercivity and high‐temperature (HC_HT) magnetization component, are also almost symmetrically oriented with reference to the plane of impact. Studies on the relative displacements of K3 (minimum) AMS axes of shocked basalts from around the crater rim and from the adjacent target rocks to the approximately 2–3 km west of the crater center suggest that the impact stress could have branched out into the major southwestward and northwestward components in the downrange direction immediately after the impact. The biaxial distribution of AMS axes in stereographic plots for the unshocked basalts transforms mostly into triaxial distribution for the shocked basalts, although transitional type distribution also exists. The degree of anisotropy (P′) of AMS ellipsoids of the shocked basalts decreases by approximately 2% when compared with those of the unshocked target (approximately 1.03). The NRM/χ (Am?1) values of the shocked basalts on the rim of the Lonar crater do not show much change in the uprange or downrange direction on and close to the east–west plane of impact, and the values are only approximately 1.5 times higher on average over the unshocked basalts around the crater. However, the values become approximately 1.4–16.4 times higher for the shocked basalts on the crater rim, which occur obliquely to the plane of impact. The target basalts at approximately 2–3 km west of the crater center in the downrange also show a significant increase (up to approximately 26 times higher) in NRM/χ. The majority of the shocked basalt samples (approximately 73%) from around the crater rim, in general, show a lowering of REM, except those from approximately 2–3 km west of the crater center in the downrange, where nearly half of the sample population shows a higher REM of approximately 3.63% in average. The shocked target basalts around the Lonar crater also acquired an HC_HT magnetization component due to impact. These HC_HT components are mostly oriented in the uprange direction and are symmetrically disposed about the east–west plane of impact, making an obtuse angle with the direction of impact. The low‐coercivity and low‐temperature (LC_LT) components of both the unshocked and shocked basalts are statistically identical to the present day field (PDF) direction. This could be chemical and/or viscous remanent magnetization acquired by the target basalts during the last 570 ± 47 ka, subsequent to the formation of the Lonar crater. The shocked Lonar target basalts appear to have remagnetized under high impact shock pressure and at low temperature of approximately 200–300 °C, where Ti‐rich titanomagnetite was the main magnetic remanence carrier.  相似文献   

14.
Lunar rock magnetism   总被引：2，自引：0，他引：2  
The relationship between the magnetization and temperature in a high constant magnetic field for a temperature range between 5 K and 1100 K was examined for Apollo 11, 12 and 14 lunar materials. The average value of Curie point temperature is (768.2 ± 3.5)°C for the lunar igneous rocks and (762.5 ± 3.4)°C for the lunar fines and breccias. A tentative conclusion about the ferromagnetic substance in the lunar materials would be that Fe is absolutely dominant with a slight association of Ni and Co, and probably Si also, in the lunar native irons.The antiferromagnetic phase of ilmenite and the paramagnetic phase of pyroxenes are considerably abundant in all lunar materials. However, a discrepancy of observed magnetization from a simulated value based on known magnetic elements for the temperature range between 10 and 40 K suggests that pyroxene phase represented by (M x Fe1-x ) SiO3 (whereM = Ca2+, Mg2+, etc and 0 x 1/4) also may behave antiferromagnetically.Magnetic hysteresis curves are obtained at 5 K and 300 K, and the viscous magnetic properties also are examined for a number of lunar materials. The superparamagnetically viscous magnetization has been experimentally proven as due to fine grains of metallic iron less than 200 Å in mean diameter. The viscous magnetization is dominant in the lunar fines and breccias which is classified into Type II, while it is much smaller than the stable magnetic component in lunar igneous rocks (Type I). The superparamagnetically fine particles of metallic iron are mostly blocked at 5 K in temperature; thus coercive force (H c ) and saturation remanent magnetization (I R ) become much large at 5 K as compared with the corresponding values at 300 K.Strongly impact-metamorphosed parts of lunar breccias have an extremely stable NRM which could be attributed to TRM. NRM of the lunar igneous rocks and majority of breccias (or clastic rocks) are intermediately stable, but their stability is considerably higher than that of IRM of the same intensity. This result may imply that some mechanism which causes an appreciable magnitude of NRM and the higher stability, such as the shock effect, may take place on the lunar surface in addition to TRM mechanism for special cases.A particular igneous rock (Sample 14053) is found to have an unusually strong magnetism owing to a high content of metallic iron (about 1 weight percent), and its NRM amounts to 2 × 10–3 emu/g. The abundance of such highly magnetic rocks is not known as yet but it seems that the observed magnetic anomalies on the lunar surface could be related to such highly magnetized rock masses.  相似文献   

15.
We present results of a magnetic survey of achondritic meteorites, representing the aubrites (A), diogenites (D), Irowardites (H), and eucrites (E) groups and relate their magnetic behavior to respective class characteristics and models of origin.Magnetic susceptibility (x) values cluster well within each group and decrease systematically between groups (from 2 to 0.1×10–3GOe–1 cm–3), with the average metal contents, (from 1 to <0.1 wt%) in the above order. The natural remanent magnetization (NRM) values range broadly within each group, but group averages decrease roughly as above. However, the considerable within-sample and intra-group variability in NRM level and its demagnetization characteristics attest to inhomogeneous and localized brecciation effects. Although petrological-chemical studies resolve a primary component of magmatic differentiation on the planetoid of origin, no clear magnetic record of such event has been preserved. The magnetization of achondrites is mainly the product of their complex, multi-stage impact brecciation and metamorphism history, in accord with other lines of evidence.The magnetic behavior of achondrites is remarkably similar to that characteristic of lunar breccias and impact-melt rocks and reinforces their analogous mode of genesis, as brought out by chemical and petrographic analyses.  相似文献   

16.
Haughton is a ~24 Myr old midsize (apparent diameter 23 km) complex impact structure located on Devon Island in Nunavut, Canada. The center of the structure shows a negative gravity anomaly of ?12 mGal coupled to a localized positive magnetic field anomaly of ~900 nT. A field expedition in 2013 led to the acquisition of new ground magnetic field mapping and electrical resistivity data sets, as well as the first subsurface drill cores down to 13 m depth at the top of the magnetic field anomaly. Petrography, rock magnetic, and petrophysical measurements were performed on the cores and revealed two different types of clast‐rich polymict impactites: (1) a white hydrothermally altered impact melt rock, not previously observed at Haughton, and (2) a gray impact melt rock with no macroscopic sign of alteration. In the altered core, gypsum is present in macroscopic veins and in the form of intergranular selenite associated with colored and zoned carbonate clasts. This altered core has a natural remanent magnetization (NRM) four to five times higher than materials from the other core but the same magnetic susceptibility. Their magnetization is still higher than the surrounding crater‐fill impact melt rocks. X‐ray fluorescence data indicate a similar proportion of iron‐rich phases in both cores and an enrichment in silicates within the altered core. In addition, alternating‐field demagnetization results show that one main process remagnetized the rocks. These results support the hypothesis that intense and possibly localized post‐impact hydrothermal alteration enhanced the magnetization of the clast‐rich impact melt rocks by crystallization of magnetite within the center of the Haughton impact structure. Subsequent erosion was followed by in situ concentration in the subsurface leading to large magnetic gradient on surface.  相似文献   

17.
We describe a new approach to estimate asteroid masses from planetary range measurements. The approach significantly simplifies the process of parameter estimation and allows an effective control of systematic errors introduced by the omission of asteroids from the dynamical model. All asteroid masses are adjusted individually thus avoiding the usual distinction between masses considered individually and masses based on densities within the C, S and M taxonomic classes. Regularization is achieved by accounting, on each mass, for a prior uncertainty determined from available estimations of asteroid diameters and densities.The new approach is used to fit the asteroid model of the JPL planetary ephemeris to Mars range data. The adjusted planetary solutions exhibit similar extrapolation capacity as previous releases of the JPL ephemeris. Up to 27 asteroid masses are determined to better than 35%. The masses agree well with estimates obtained independently by other authors. The determined masses are also robust with respect to cross-validation on a dataset with a shorter time-span and with respect to a different selection of asteroids in the model.  相似文献   

18.
Abstract— The magnetic properties of the Millbillillie eucrite have been intensively studied using mutually oriented samples. The magnetic carrier has been identified as single domain/pseudo-single domain kamacite. It is believed that due to clast-rich/clast-poor layering, the rock has been subjected to minimum shock since formation. This is supported by the presence of a stable, unidirectional remanence. Three separate palaeointensity tests (IRM/NRM, ARM-NRM, and Thellier heating) have been used to determine the strength of the palaeofield. The criteria for the suitability of samples to be used in such tests are discussed, as are the three methods; IRM/NRM is deemed the least accurate. The results obtained (IRM/NRM: 6 μT and 25 μT; ARM-NRM: 31 μT, 28 μT, and 15 μT; Thellier: 30 μT, 37 μT, 15 μT) indicate that the rock cooled in a strong magnetic field. Modes of formation, given that Millbillillie has a layered structure, and the nature of the HED parent body, are discussed. A volcanic genesis is preferred over formation in an impact melt. An internal dynamo field is favoured for dynamical reasons, and calculations based on the assumption that 4 Vesta is a possible HED parent body indicate that an iron core may be present in such a body.  相似文献   

19.
High resolution spectroscopic observations of asteroid 2 Pallas from 1.7-3.5 μm are reported. These data are combined with previous measurements from 0.4-1.7 μm to interpret Pallas' surface mineralogy. Evidence is found for low-Fe2+ hydrated silicates, opaque components, and low-Fe2+ anhydrous silicates. This assemblage is very similar to carbonaceous chondrite matrix material such as is found in type CI and CM meteorites, but it has been subjected to substantial aqueous alteration and there is a major extraneous anhydrous silicate component. This composition is compared to that of asteroid 1 Ceres. Although there are substantial differences in their broad band spectral reflectances, it appears that both asteroids are genetically related to known carbonaceous chondrites.  相似文献   

20.
Space weathering and the interpretation of asteroid reflectance spectra   总被引：1，自引：0，他引：1  
Michael J. Gaffey 《Icarus》2010,209(2):564-574
Lunar-style space weathering is well understood, but cannot be extended to asteroids in general. The two best studied Asteroids (433 Eros and 243 Ida) exhibit quite different space weathering styles, and neither exhibits lunar-style space weathering. It must be concluded that at this time the diversity and mechanisms of asteroid space weathering are poorly understood. This introduces a significant unconstrained variable into the problem of analyzing asteroid spectral data. The sensitivity of asteroid surface material characterizations to space weathering effects - whatever their nature - is strongly dependent upon the choice of remote sensing methodology. The effects of space weathering on some methodologies such as curve matching are potentially devastating and at the present time essentially unmitigated. On other methodologies such as parametric analysis (e.g., analyses based on band centers and band area ratios) the effects are minimal. By choosing the appropriate methodology(ies) applied to high quality spectral data, robust characterizations of asteroid surface mineralogy can be obtained almost irrespective of space weathering. This permits sophisticated assessments of the geologic history of the asteroid parent bodies and of their relationships to the meteorites. Investigations of the diversity of space weathering processes on asteroid surfaces should be a fruitful area for future efforts.  相似文献   

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