Ponded deposits on asteroid 433 Eros Cheng, A. F.; Izenberg, N.; Chapman, C. R. ...
Meteoritics & planetary science,
August 2002, Letnik:
37, Številka:
8
Journal Article
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— In late January 2001 the NEAR—Shoemaker spacecraft performed low‐altitude passes over the surface of 433 Eros. Coordinated observations of the asteroid surface were obtained at submeter resolution ...by the NEAR laser rangefinder and the multispectral imager. This paper presents three independent, coordinated observations of a 90 m pond adjacent to a granular debris flow, including the highest resolution altimetric measurements of ponded deposits on Eros. The ponded deposits appear to have been emplaced by fluid‐like motion of dry asteroidal regolith. A simple model of seismic agitation from impacts is developed to account for pond formation on Eros. The model predicts that ponds should form readily on Eros but not on the Moon, where ponds are not observed. The model also suggests that the absence of observable ponds in the largest craters of Eros, as well as on Phobos and Deimos, may be related to regolith depth.
On 27 June 1997, the Near Earth Asteroid Rendezvous (NEAR) spacecraft flew within 1212 kilometers of asteroid 253 Mathilde. Mathilde is an irregular, heavily cratered body measuring 66 kilometers by ...48 kilometers by 46 kilometers. The asteroid's surface is dark (estimated albedo between 0.035 and 0.050) and similar in color to some CM carbonaceous chondrites. No albedo or color variations were detected. The volume derived from the images and the mass from Doppler tracking of the spacecraft yield a mean density of 1.3 ± 0.2 grams per cubic centimeter, about half that of CM chondrites, indicating a porous interior structure.
From February 13 to May 13, 2000, the near-infrared spectrometer (NIS) instrument on the Near Earth Asteroid Rendezvous (NEAR) spacecraft obtained more than 200,000 spatially resolved 800- to 2500-nm ...reflectance spectra of the S-type asteroid 433 Eros. An important subset of the spectra was obtained during a unique opportunity on February 13 and 14, when the NEAR spacecraft flew directly through the 0° phase angle point between Eros and the Sun just prior to the orbital insertion maneuver. This low phase flyby (LPF) dataset consists of ∼2000 spectra of the northern hemisphere of Eros, obtained from 1° to 47° phase angle and at spatial resolutions of between 6×12 km to 1.25×2.50 km per spectrum. The spectra were calibrated to radiance factor (I/F, where I=observed radiance and πF=solar input radiance) and then photometrically corrected to normal albedo. The average northern hemisphere spectrum of Eros is similar to the asteroid's unresolved telescopic spectrum and exhibits absorption features near 1000 nm (Band I) and 2000 nm (Band II) consistent with an orthopyroxene to orthopyroxene+olivine (opx+ol) mixing ratio of approximately 0.38±0.08. The ensemble of NIS LPF spectra falls primarily within the S(IV) to upper S(III) fields of the Gaffey et al. (1993) S-asteroid classification scheme and exhibits Band I and Band II properties similar to those of ordinary chondrite meteorites. While some small spatially coherent spectral variations have been detected, neither the opx/opx+ol) mixing ratio nor other spectral parameters vary spatially by more than ∼1σ across the entire northern hemisphere of the asteroid, suggesting a remarkable homogeneity of the composition and mineralogy of the uppermost regolith. Spectral mixture modeling suggests that the presence of glass and/or a reddening agent like nanophase iron, likely formed from exposure of the regolith to the space environment, is a component of the surface of Eros. Reddening and darkening components could also explain the dissimilarity in overall spectral slope and albedo between Eros and other S(IV) asteroids and ordinary chondrite meteorites. The largest (but still weak) spectral variations across the surface are seen in the depths of Band I and Band II, which are greatest in and around the largest craters and at the 0° longitude “nose” of the asteroid, and in the Band II/Band I area ratio between the large impact craters Psyche and Himeros. These subtle NIS spectral variations are usually associated with albedo and surface slope variations seen in NEAR imaging and topographic data and appear to be related to downslope movement of regolith materials.
— The near‐Earth asteroid rendezvous (NEAR) mission carried x‐ray/gamma‐ray spectrometers and multi‐spectral imager/near‐infrared spectrometer instrument packages which gave complementary information ...on the chemistry and mineralogy, respectively, of the target asteroid 433 Eros. Synthesis of these two data sets provides information not available from either alone, including the abundance of non‐mafic silicates, metal and sulfide minerals. We have utilized four techniques to synthesize these data sets. Venn diagrams, which examine overlapping features in two data sets, suggest that the best match for 433 Eros is an ordinary chondrite, altered at the surface of the asteroid, or perhaps a primitive achondrite derived from material mineralogically similar to these chondrites. Normalized element distributions preclude FeO‐rich pyroxenes and suggest that the x‐ray and gamma‐ray data can be reconciled with a common silicate mineralogy by inclusion of varying amounts of metal. Normative mineralogy cannot be applied to these data sets owing to uncertainties in oxygen abundance and lack of any constraints on the abundance of sodium. Matrix inversion for simultaneous solution of mineral abundances yields reasonable results for the x‐ray‐derived bulk composition, but seems to confirm the inconsistency between mineral compositions and orthopyroxene/clinopyroxene ratios. A unique solution does not seem possible in synthesizing these multiple data sets. Future missions including a lander to fully characterize regolith distribution and sample return would resolve the types of problems faced in synthesizing the NEAR data.
On 25 October 2000, the Near Earth Asteroid Rendevous (NEAR)-Shoemaker spacecraft executed a low-altitude flyover of asteroid 433 Eros, making it possible to image the surface at a resolution of ...about 1 meter per pixel. The images reveal an evolved surface distinguished by an abundance of ejecta blocks, a dearth of small craters, and smooth material infilling some topographic lows. The subdued appearance of craters of different diameters and the variety of blocks and different degrees of their burial suggest that ejecta from several impact events blanketed the region imaged at closest approach and led to the building up of a substantial and complex regolith consisting of fine materials and abundant meter-sized blocks.
— We present combined multi‐spectral imager (MSI) (0.95 μm) and near‐infrared spectrometer (NIS) (0.8–2.4 μm) observations of Psyche crater on S‐type asteroid 433 Eros obtained by the Near‐Earth ...Asteroid Rendezvous (NEAR)—Shoemaker spacecraft. At 5.3 km in diameter, Psyche is one of the largest craters on Eros which exhibit distinctive brightness patterns consistent with downslope motion of dark regolith material overlying a substrate of brighter material. At spatial scales of 620 m/ spectrum, Psyche crater wall materials exhibit albedo contrasts of 32–40% at 0.946 μm. Associated spectral variations occur at a much lower level of 4–8% (±2–4%). We report results of scattering model and lunar analogy investigations into several possible causes for these albedo and spectral trends: grain size differences, olivine, pyroxene, and troilite variations, and optical surface maturation. We find that the albedo contrasts in Psyche crater are not consistent with a cause due solely to variations in grain size, olivine, pyroxene or lunar‐like optical maturation. A grain size change sufficient to explain the observed albedo contrasts would result in strong color variations that are not observed. Olivine and pyroxene variations would produce strong band‐correlated variations that are not observed. A simple lunar‐like optical maturation effect would produce strong reddening that is not observed. The contrasts and associated spectral variation trends are most consistent with a combination of enhanced troilite (a dark spectrally neutral component simulating optical effects of shock) and lunar‐like optical maturation. These results suggest that space weathering processes may affect the spectral properties of Eros materials, causing surface exposures to differ optically from subsurface bedrock. However, there are significant spectral differences between Eros' proposed analog meteorites (ordinary chondrites and/or primitive achondrites), and Eros' freshest exposures of subsurface bright materials. After accounting for all differences in the measurement units of our reflectance comparisons, we have found that the bright materials on Eros have reflectance values at 0.946 μm consistent with meteorites, but spectral continua that are much redder than meteorites from 1.5 to 2.4 μm. Most importantly, we calculate that average Eros surface materials are 30–40% darker than meteorites.
Space weathering is an important process on airless bodies, and it must be considered when interpreting data from planetary missions. Previous work has shown that solar energetic particles may cause ...dielectric breakdown in regolith within permanently shadowed regions near the poles of the Moon. Here, we predict that dielectric breakdown weathering could have melted and/or vaporized 2−9% of gardened (i.e., thoroughly mixed) regolith at the equator and 5−11% near the poles. If so, then ∼3−10% of all gardened regolith on the Moon may have experienced dielectric breakdown, and this process must be considered when analyzing remote sensing data or soil samples returned by the Luna and Apollo missions.
Egon Schiele (1890-1918) was a leading figure of second-generation Viennese modernism. Appreciated in his time as an extraordinary draughtsman, he was also notorious for the blatant eroticism of his ...young female nudes and the ruthless honesty of his tortured self-portraits. A historically informed psychoanalytic approach reveals both the intrapsychic and psychohistorical significance of his work.
Schiele's explorations in portraiture were partly the product of internal conflicts on many levels. But they were also refracted through a turn-of-the-century crisis in European masculine identity. The crisis was born of social and political developments that worked to undermine middle-class males' sense of power and self-esteem, among them the woman's movement and a new cultural awareness of the psychological power of mothers and of female sexuality. These factors were especially powerful in the psychology of artists, who often felt both marginal and effeminate in a culture that valued the manly virtues of the warrior and the entrepreneur. Their effects are reflected in the fragmented self-images, overpowering mothers, and seductively self-certain girls and women of Schiele's paintings.
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Dostopno za:
BFBNIB, DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
Although largely sympathetic to Freud's clinical achievement, the existentialists criticized Freudian metapsychology as inappropriate to a truly humanistic psychology. Gerald Izenberg evaluates the ...critique of Freud in the work of two existential philosophers, Martin Heidegger and Jean-Paul Sartre, and two existential psychiatrists, Ludwig Binswanger and Medard Boss.
His book interprets the relationship of psychoanalysis and existentialism and traces the history of a crisis in the European rationalist tradition. The author unveils the positivist foundations of Freud's theory of meaning and discusses the reactions it provoked in the work of Binswanger, Boss, and Sartre. Probing beneath the methodological dispute, he shows that the argument involved a challenge to the conception of the self that had dominated European thought since the Enlightenment. Existentialism, reflecting the turmoil of the inter-war and post-war years, furnished a theory of motivation better able to account for Freud's clinical data than his own rationalist metapsychology. This theory made problematic the existentialist idea of authenticity and freedom, however, and so the attempt to provide a substitute ethic and concept of mental health ended in failure, although in the process the basic questions were posed that must be answered in any modern social theory.
Originally published in 1976.
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