NEAR at Eros: Imaging and Spectral Results

Veverka, J.; Robinson, M. S.; Thomas, P. C.; Murchie, S. L.; Bell, James F.; Izenberg, N. R.; Chapman, C. R.; Harch, A.; Bell, Maureen; Carcich, B.; Cheng, A. F.; Clark, B. E.; Domingue, D. L.; Dunham, David; Farquhar, Robert W.; Gaffey, M. J.; Hawkins, E.; Joseph, J.; Kirk, Randolph L.; Li, H.; Lucey, P. G.; Malin, M. C.; Martin, Patrick; McFadden, L. A.; Merline, W. J.; Miller, James; Owen, W. M.; Peterson, C.; Prockter, L. M.; Warren, J.; Wellnitz, D. D.; Williams, Bobby G.; Yeomans, Donald K.

doi:10.1126/science.289.5487.2088

Cited by 263 publications

(191 citation statements)

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“…Preliminary reports on the geology of Eros have been presented by Veverka et al (2000Veverka et al ( , 2001, Thomas et al (2002) and Murchie et al (2002). In their paper, Thomas et al (2002) compare Psyche crater with other craters on Eros.…”

Section: Previous Workmentioning

confidence: 99%

Space weathering on Eros: Constraints from albedo and spectral measurements of Psyche crater

Clark

Lucey

Helfenstein

et al. 2001

Meteorit & Planetary Scien

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Abstract-We present combined multi-spectral imager (MSI) (0.95 pm) and near-infrared spectrometer (NIS) (0.8-2.4pm) observations of Psyche crater on S-type asteroid 433 Eros obtained by the NearEarth 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 of620 m/ spectrum, Psyche crater wall materials exhibit albedo contrasts of 3 2 4 0 % at 0.946 pm. 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 0.946pm consistent with meteorites, but spectral continua that are much redder than meteorites from 1.5 to 2.4 pm. Most importantly, we calculate that average Eros surface materials are 3040% darker than meteorites.

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Section: Previous Workmentioning

confidence: 99%

Space weathering on Eros: Constraints from albedo and spectral measurements of Psyche crater

Clark

Lucey

Helfenstein

et al. 2001

Meteorit & Planetary Scien

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“…1), coarsely approximated by an ellipsoid of dimensions 33 x 11 x 11 km, and has a mean radius of 8.5 km. It has a spin period of 5.27 h and a rotational obliquity of88° (Thomas et a!., 2002a;Veverka et al, 1999Veverka et al, ,2000. Periapsis of the orbit is at 1.13 AU, and apoapsis at 1.73 AU ( Table 1).…”

Section: Introductionmentioning

confidence: 99%

The geology of 433 Eros

Robinson

Thomas

Veverka

et al. 2002

Meteorit & Planetary Scien

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Abstract-The global high-resolution imaging of asteroid 433 Eros by the Near-Earth Asteroid Rendezvous (NEAR) Shoemaker spacecraft has made it possible to develop the first comprehensive picture of the geology of a small S-type asteroid. Eros displays a variety of surface features, and evidence of a substantial regolith. Large scale facets, grooves, and ridges indicate the presence of at least one global planar structure. Directional and superposition relations of smaller structural features suggest that fracturing has occurred throughout the object. As with other small objects, impact craters dominate the overall shape as well as the small-scale topography of Eros. Depth/diameter ratios of craters on Eros average -0.13, but the freshest craters approach lunar values of -0.2. Ejecta block production from craters is highly variable; the majority oflarge blocks appear to have originated from one 7.6 km crater (Shoemaker). The interior morphology of craters does not reveal the influence of discrete mechanical boundaries at depth in the manner of craters formed on lunar mare regolith and on some parts of Phobos. This lack of mechanical boundaries, and the abundant evidence of regolith in nearly every high-resolution image, suggests a gradation in the porosity and fracturing with depth. The density of small craters is deficient at sizes below -200 m relative to predicted slopes of empirical saturation. This characteristic, which is also found on parts ofPhobos and lunar highland areas, probably results from the efficient obliteration of small craters on a body with significant topographic slopes and a thick regolith. Eros displays a variety ofregolith features, such as debris aprons, fine-grained "ponded" deposits, talus cones, and bright and dark streamers on steep slopes indicative ofefficient downslope movement ofregolith. These processes serve to mix materials in the upper loose fragmental portion ofthe asteroid (regolith). In the instance of "ponded" materials and crater wall deposits, there is evidence of processes that segregate finer materials into discrete deposits. The NEAR observations have shown us that surface processes on small asteroids can be very complex and result in a wide variety of morphologic features and landforms that today seem exotic. Future missions to comets and asteroids will surely reveal still as yet unseen processes as well as give context to those discovered by the NEAR Shoemaker spacecraft.

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“…The most heavily cratered, and therefore oldest, regions (Noricum and Achaia) are separated by the Narbonensis region, which is defined by a crater of ~55 km in diameter ( commonly interpreted as resulting from a large impact (11). On 433 Eros, the existence of similar grooves has been interpreted as evidence of competent rock below the regolith, although this asteroid is thought to be heavily fractured (12,13,14). Recent work suggests that cracks can be supported in very low strength material on a body as small as Eros (15).…”

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Images of Asteroid 21 Lutetia: A Remnant Planetesimal from the Early Solar System

Sierks

Lamy

Barbieri

et al. 2011

Science

189

132

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Images obtained by the Optical, Spectroscopic, and Infrared Remote Imaging System (OSIRIS) cameras onboard the Rosetta spacecraft reveal that asteroid 21 Lutetia has a complex geology and one of the highest asteroid densities measured so far, 3.4 ± 0.3 grams per cubic centimeter. The north pole region is covered by a thick layer of regolith, which is seen to flow in major landslides associated with albedo variation. Its geologically complex surface, ancient surface age, and high density suggest that Lutetia is most likely a primordial planetesimal. This contrasts with smaller asteroids visited by previous spacecraft, which are probably shattered bodies, fragments of larger parents, or reaccumulated rubble piles

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NEAR at Eros: Imaging and Spectral Results

Cited by 263 publications

References 50 publications

Space weathering on Eros: Constraints from albedo and spectral measurements of Psyche crater

Space weathering on Eros: Constraints from albedo and spectral measurements of Psyche crater

The geology of 433 Eros

Images of Asteroid 21 Lutetia: A Remnant Planetesimal from the Early Solar System

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