Ejecta Emplacement on the Martian Satellites

Thomas, P. C.

doi:10.1006/icar.1997.5858

Cited by 47 publications

(60 citation statements)

References 49 publications

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“…the excavated volume (about one half the volume of the crater cavities) of all craters and assuming a conservative retention rate of25% to 50% (Asphaug and Melosh, 1993). This retention rate, not intuitively obvious because of the low gravity, has been supported observationally by comparison of estimates of Phobos' total ejecta volume and models of ejecta distribution across its surface (Thomas, 1998). For Eros we summed the excavated volume of all craters larger than 1 km in diameter (89 kmt) and divided this value by Eros' area (1125 km 2 ) to derive an average regolith depth 0[20--40 m (retention of25-50%) .…”

Section: Regolithmentioning

confidence: 77%

“…The Phobos data (from Thomas, 1998;Thomas et al, 2000) include a global data set (>700 m diameter), and some local data at good viewing down to pixel scales of -4 ill. The Phobos and Eros crater densities between 30 and 200 m are similar except for the steep topography (slopes _20°) within Stickney crater, which has a substantially lower crater density.…”

Section: Impact Craters Crater Densitiesmentioning

confidence: 99%

“…For Eros we summed the excavated volume of all craters larger than 1 km in diameter (89 kmt) and divided this value by Eros' area (1125 km 2 ) to derive an average regolith depth 0[20--40 m (retention of25-50%) . On asteroids ejecta do not impact symmetrically, as they do on the Moon, due to the relatively low gravity, excursions from sphericity, and typically rapid rotationrates (Geissler eta!., 1996;Thomas, 1998). Depending on geographic location, and an asteroid's gravity and spin rate, ejecta thickness around a crater rim can easily differ by factors of2 or more (Thomas, 1998).…”

Section: Regolithmentioning

confidence: 99%

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The geology of 433 Eros

Robinson

Thomas

Veverka

et al. 2002

Meteorit & Planetary Scien

155

140

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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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Section: Regolithmentioning

confidence: 77%

Section: Impact Craters Crater Densitiesmentioning

confidence: 99%

Section: Regolithmentioning

confidence: 99%

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The geology of 433 Eros

Robinson

Thomas

Veverka

et al. 2002

Meteorit & Planetary Scien

155

140

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“…In evaluating the present state of Stickney, two "environmental" conditions need to be considered: Stickney probably formed in the gravity regime (processes dominated by gravity rather than by material strength); [Melosh, 1989;Asphaug and Melosh, 1993;Nolan et al, 1996], and it may have formed when Phobos was farther from Mars than at present [Dobrovolskis and Burns, 1980]. Formation in the gravity regime is predicted by many hydrocode simulations, and the gross distribution of ejecta on Phobos and Deimos appears consistent with this prediction [Thomas, 1998]. The primary implications of gravity regime formation in the context of this study are that ejecta distribution about the crater is essentially geometrically similar over a large size range, and the fraction of ejecta that can escape (from a crater of a specified fraction of the target's diameter) is roughly the same for targets of very different sizes [Asphaug and Melosh, 1993;Housen et al, 1983 ].…”

Section: Interior Morphology Of Crater Stickneymentioning

confidence: 99%

“…The primary implications of gravity regime formation in the context of this study are that ejecta distribution about the crater is essentially geometrically similar over a large size range, and the fraction of ejecta that can escape (from a crater of a specified fraction of the target's diameter) is roughly the same for targets of very different sizes [Asphaug and Melosh, 1993;Housen et al, 1983 ]. Because of Phobos's position close to Mars, the satellite is subject to considerable rotational and tidal effects which are predicted to cause significant east-west asymmetry in crater ejecta dispersal [Davis et al, 198I;Thomas, 1998]. Furthermore, this asymmetry depends very strongly on distance from Mars.…”

Section: Interior Morphology Of Crater Stickneymentioning

confidence: 99%

Phobos: Regolith and ejecta blocks investigated with Mars Orbiter Camera images

Thomas¹,

Veverka²,

Sullivan³

et al. 2000

J. Geophys. Res.

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Excavating Stickney crater at Phobos

Syal

Rovny

Owen

et al. 2016

Geophysical Research Letters

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Stickney crater, at 9 km across, dominates the morphology of ~22 km Phobos, the larger of the two moons of Mars. The Stickney impact event had global repercussions for Phobos, including extensive resurfacing and fracturing of the moon. Understanding the initial conditions and dynamical consequences of the collision is necessary to test competing hypotheses for the origin of peculiar grooved terrain that striates much of the surface. Previous modeling of the impact event was unable to replicate Stickney without globally fragmenting the satellite. Here we describe high‐resolution numerical simulations that successfully generate Stickney crater while maintaining the large‐scale structure of Phobos. Target porosity, which is estimated to be significant, aids in keeping the moon intact. Damage follows patterns centered on Stickney that are inconsistent with the observed alignment of grooved terrain on Phobos. Low‐velocity boulders are ejected at shallow angles in sufficient numbers to support a rolling‐boulder origin for grooved terrain.

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Ejecta Emplacement on the Martian Satellites

Cited by 47 publications

References 49 publications

The geology of 433 Eros

The geology of 433 Eros

Phobos: Regolith and ejecta blocks investigated with Mars Orbiter Camera images

Excavating Stickney crater at Phobos

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