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321.
William K. Hartmann Paolo Farinella David Vokrouhlický Stuart J. Weidenschilling Alessandro Morbidelli Francesco Marzari Donald R. Davis Eileen Ryan 《Meteoritics & planetary science》1999,34(Z4):A161-A167
Abstract— We give a nonmathematical review of recent work regarding the Yarkovsky effect on asteroidal fragments. This effect may play a critical, but underappreciated, role in delivering meteorites to Earth. Two variants of the effect cause drifts in orbital elements, notably semimajor axes. The “classic” or “diurnal” Yarkovsky effect is associated with diurnal rotation at low obliquity. More recently, a “seasonal” effect has also been described, associated with high obliquity. Studies of these Yarkovsky effects are combined with studies of resonance effects to clarify meteorite delivery. If there were no Yarkovsky drift, asteroid fragments could reach a resonance only if produced very near that resonance. However, objects in resonances typically reach Earth-crossing orbits within a few million years, which is inconsistent with stone meteorites' cosmic-ray exposure (CRE) ages (5–50 Ma) and iron meteorites' CRE ages (100–1000 Ma). In the new view, on the other hand, large objects in the asteroid belt are “fixed” in semimajor axis, but bodies up to 100 m in diameter are in a constant state of mixing and flow, especially if the thermal conductivity of their surface layers is low. Thus, small asteroid fragments may reach the resonances after long periods of drift in the main belt. Yarkovsky drift effects, combined with resonance effects, appear to explain many meteorite properties, including: (1) the long CRE ages of iron meteorites (due to extensive drift lifetimes in the belt); (2) iron meteorites' sampling of numerous parent bodies; (3) the shorter CRE ages of most stone meteorites (due to faster drift, coupled with weaker strength and more rapid collisional erosion); and (4) the abundance of falls from discrete impact events near resonances, such as the 8 Ma CRE age of H chondrites. Other consequences include: the delivery of meteorite parent bodies to resonances is enhanced; proportions of stone and iron meteorites delivered to Earth may be different from the proportions at the same sizes left in the belt, which in turn may differ from the ratio produced in asteroidal collisions; Rabinowitz's 10–100 m objects may be preferentially delivered to near-Earth space; and the delivery of C-class fragments from the outer belt may be inhibited, compared to classes in other parts of the belt. Thus, Yarkovsky effects may have important consequences in meteoritics and asteroid science. 相似文献
322.
323.
Kevin Righter Ryan S. Jakubek Marc D. Fries John Schutt Kellye Pando Roger Harrington 《Meteoritics & planetary science》2023,58(1):25-40
Carbonaceous chondrites of the Vigarano group (CV) are primitive (nearly un-metamorphosed) meteorites that provide a wealth of information about the early solar system, including constraints on chondrule formation, origin of calcium-aluminum inclusions, stability of organic compounds, and redox conditions. The US Antarctic meteorite collection contains 119 CV samples from 15 dense collection areas (DCAs) from the TransAntarctic Mountains; these samples have been assigned a preliminary classification as CVs, but not to the subgroups oxidized A, oxidized B, and reduced. Furthermore, variation in petrologic grade can be determined non-destructively using Raman spectroscopy. To update the classification of both subgroups and petrologic types in the collection, we have acquired magnetic susceptibility, metal and sulfide compositions, and Raman spectra. Overall, there are 55 oxidized A samples, 18 oxidized B samples, and 46 reduced samples. Several of the CVs are quite primitive (Lewis Cliffs Ice Tongue and MacAlpine Hills) but are also very small. Multiple pairing groups have been identified in the Miller Range (MIL), Queen Alexandra Range, and Larkman Nunatak DCAs, including all of the subgroups. In MIL 090981, there is evidence for multiple lithologies. We make suggested updates for all the samples, knowing that this information will help to better guide researchers interested in studying the CV chondrites in the US Antarctic meteorite collection. 相似文献
324.
Margaret R. Mulholland Ryan E. Morse George E. Boneillo Peter W. Bernhardt Katherine C. Filippino Leo A. Procise Jose L. Blanco-Garcia Harold G. Marshall Todd A. Egerton William S. Hunley Kenneth A. Moore Dianna L. Berry Christopher J. Gobler 《Estuaries and Coasts》2009,32(4):734-747
During August and September 2007, the lower Chesapeake Bay and its tributaries experienced a massive bloom of Cochlodinium polykrikoides Margalef (>104 cells per milliliter) that persisted for over a month, was extremely patchy, and at times penetrated into the Atlantic Ocean. The onset of the bloom coincided with a period of intense rainfall and stormwater runoff after a protracted summer drought period. Genetic evidence showed this species to be distinct from many Asian strains but similar to other North American strains. Populations dominated by C. polykrikoides took up a variety of nitrogenous compounds to support their growth and were able to mobilize additional sources of organic nutrients through peptide hydrolysis. Bioassays determined that C. polykrikoides exerted a lethal affect on juvenile fish and shellfish, causing 100% mortality of juvenile fish (Cyprinodon variegates) in less than 24 h and 20% mortality in juvenile American oysters (~21 mm; Crassostrea virginica) within 72 h. 相似文献
325.
326.
Perturbed two-body problems play a special role in Celestial Mechanics as they capture the dominant dynamics for a broad range
of natural and artificial satellites. In this paper, we investigate the classic Stark problem, corresponding to motion in
a Newtonian gravitational field subjected to an additional uniform force of constant magnitude and direction. For both the
two-dimensional and three-dimensional cases, the integrals of motion are determined, and the resulting quadratures are analytically
integrated. A complete list of exact, closed-form solutions is deduced in terms of elliptic functions. It is found that all
expressions rely on only seven fundamental solution forms. Particular attention is given to ensure that the expressions are
well-behaved for very small perturbations. A comprehensive study of the phase space is also made using a boundary diagram
to describe the domains of the general types of possible motion. Numerical examples are presented to validate the solutions. 相似文献
327.
Ryan L. Kobrick David M. Klaus Kenneth W. Street Jr. 《Planetary and Space Science》2011,59(14):1749-1757
Unexpected issues were encountered during the Apollo era of lunar exploration due to detrimental abrasion of materials upon exposure to the fine-grained, irregular shaped dust on the surface of the Moon. For critical design features involving contact with the lunar surface and for astronaut safety concerns, operational concepts and dust tolerance must be considered in the early phases of mission planning. To systematically define material selection criteria, dust interaction can be characterized by two-body or three-body abrasion testing, and sub-categorically by physical interactions of compression, rolling, sliding, and bending representing specific applications within the system. Two-body abrasion occurs when a single particle or asperity slides across a given surface removing or displacing material. Three-body abrasion occurs when multiple particles interact with a solid surface, or in between two surfaces, allowing the abrasives to freely rotate and interact with the material(s), leading to removal or displacement of mass. Different modes of interaction are described in this paper along with corresponding types of tests that can be utilized to evaluate each configuration. In addition to differential modes of abrasion, variable concentrations of dust in different zones can also be considered for a given system design and operational protocol. These zones include (1) outside the habitat where extensive dust exposure occurs, (2) in a transitional zone such as an airlock or suitport, and (3) inside the habitat or spacesuit with a low particle count. These zones can be used to help define dust interaction frequencies, and corresponding risks to the systems and/or crew can be addressed by appropriate mitigation strategies. An abrasion index is introduced that includes the level of risk, R, the hardness of the mineralogy, H, the severity of the abrasion mode, S, and the frequency of particle interactions, F. 相似文献
328.
We performed the first global survey of lunar regolith depths using Lunar Reconnaissance Orbiter Camera (LROC) data and the crater morphology method for determining regolith depth. We find that on both the lunar farside and in the nearside, non-mare regions, the regolith depth is twice as deep as it is within the lunar maria. Our data compare favorably with previous studies where such data exist. We also find that regolith depth correlates well with density of large craters (>20 km diameter). This result is consistent with the gradual formation of regolith by rock fracture during impact events. 相似文献
329.
We present a model of the absolute radiance of the disk-resolved Moon at visible to near infrared wavelengths. It has been developed in order to use the Moon as a calibration reference, particularly by space-based sensors observing the Earth. We begin with the development of Hillier et al. (Hillier, J., Buratti, B., Hill, K. [1999]. Icarus 141, 205-225) for the reflectance as a function of phase angle and base the lunar reflectance on the Clementine 0.750 μm basemap. We adopt Hapke’s (Hapke, B. [2002]. Icarus 157, 523-534) expression for the multiple scattering term, including the more accurate approximation to the Chandrasekhar H function. The geometry is based on the Jet Propulsion Laboratory Lunar Ephemeris DE 421, and the topographic slope is from the Kaguya-LALT laser altimetry (Araki, H., and 10 colleagues [2009]. Science 323, 897-900). We define three types of terrain by combining the reflectance from the Clementine basemap and the topographic model to specify maria, highlands, and crater regions, and allow mixed types between each class. Parameters of the model are solved for as a function of surface type and wavelength by comparison against data “chips” from the Robotic Lunar Observatory (ROLO; Kieffer, H.H., Stone, T.C. [2005]. Astron. J. 129, 2887-2901). The reflectance in any waveband may be computed by spectral interpolation of the model predictions relative to the scaled Apollo 16 soil spectrum. The accuracy of the model, evaluated against ROLO imagery, was found to be 2-4%. 相似文献
330.
Stefano Campagnola Nathan J. Strange Ryan P. Russell 《Celestial Mechanics and Dynamical Astronomy》2010,108(2):165-186
The announced missions to the Saturn and Jupiter systems renewed the space community interest in simple design methods for
gravity assist tours at planetary moons. A key element in such trajectories are the V-Infinity Leveraging Transfers (VILT)
which link simple impulsive maneuvers with two consecutive gravity assists at the same moon. VILTs typically include a tangent
impulsive maneuver close to an apse location, yielding to a desired change in the excess velocity relative to the moon. In
this paper we study the VILT solution space and derive a linear approximation which greatly simplifies the computation of
the transfers, and is amenable to broad global searches. Using this approximation, Tisserand graphs, and heuristic optimization
procedure we introduce a fast design method for multiple-VILT tours. We use this method to design a trajectory from a highly
eccentric orbit around Saturn to a 200-km science orbit at Enceladus. The trajectory is then recomputed removing the linear
approximation, showing a Δv change of <4%. The trajectory is 2.7 years long and comprises 52 gravity assists at Titan, Rhea, Dione, Tethys, and Enceladus,
and several deterministic maneuvers. Total Δv is only 445 m/s, including the Enceladus orbit insertion, almost 10 times better then the 3.9 km/s of the Enceladus orbit
insertion from the Titan–Enceladus Hohmann transfer. The new method and demonstrated results enable a new class of missions
that tour and ultimately orbit small mass moons. Such missions were previously considered infeasible due to flight time and
Δv constraints. 相似文献