A large crater as a probe of the internal structure of the E-type asteroid Steins

Jutzi, Martin; Michel, Patrick; Benz, W.

doi:10.1051/0004-6361/200913549

Cited by 17 publications

(13 citation statements)

References 17 publications

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“…The possibility that this ratio is relatively large for a small body has prompted attempts to explain it, such as modelling of potential impacts in terms of possible macro or micro porosity of the body (e.g. Michel et al, 2009;Jutzi et al 2010 Indeed it is more akin to the cases of (433) km and based on analysis of a data set of 205,770 asteroids, compared to 12,487 in Zappalà et al, 1995). Antiope was identified as a synchronous pair by direct imaging (Merline et al, 2000) and was later subject to an extended programme of ground based observations to accurately determine its light curve (Descamps et al, 2007).…”

Section: (2867) Steinsmentioning

confidence: 99%

The large crater on the small Asteroid (2867) Steins

Burchell

Leliwa-Kopystyński

2010

Icarus

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The maximum size of impact craters on finite bodies marks the largest impact that can occur short of impact induced disruption of the body. Recently attention has started to focus on large craters on small bodies such as asteroids and rocky and icy satellites.Here the large crater on the recently imaged asteroid (2867) Steins (with crater diameter to mean asteroid radius ratio of 0.79) is shown to follow a limit set by other similar sized bodies with moderate macroporosity (i.e. fractured asteroids). Thus whilst large, the crater size is not novel, nor does it requires Steins to possess an extremely large porosity. In one of the components of the binary asteroid (90) Antiope there is the recently reported presence of an extremely large depression, possibly a crater, with depression diameter to mean asteroid radius ratio of ~(1.4 -1.62). This is consistent with the maximum size of a crater expected from previous observations of very porous rocky bodies (i.e. rubble-pile asteroids). Finally, a relationship between crater diameter (normalised to body radius) is proposed as a function of body porosity which suggests that the doubling of porosity between fractured asteroids and rubblepile asteroids, nearly doubles the size (D/R value) of the largest crater sustainable on a rocky body.

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Section: (2867) Steinsmentioning

confidence: 99%

The large crater on the small Asteroid (2867) Steins

Burchell

Leliwa-Kopystyński

2010

Icarus

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“…The surface is covered by several craters (Keller et al 2010;A&A 531, A168 (2011) Marchi et al 2010), with a large crater (2 km) near the south pole. A rubble pile internal structure has been proposed (Jutzi et al 2010) and the equatorial bulge may have been created by the YORP effect in the past. Statistical analysis of the surface in visible wavelengths has proved that the reflectivity is very homogeneous (Leyrat et al 2010), as also expected by Dotto et al (2009).…”

Section: Introductionmentioning

confidence: 99%

Thermal properties of the asteroid (2867) Steins as observed by VIRTIS/Rosetta

Leyrat

Coradini

Erard

et al. 2011

A&A

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Context. To investigate thermal properties of the small asteroid (2867) Steins, we analyzed its surface thermal emission measured by the VIRTIS instrument during the Rosetta spacecraft (ESA) flyby that occurred in September 2008. VIRTIS performed the first thermal mapping of an asteroid surface. Aims. We determine the thermal properties of different locations at the surface of Steins and the thermal inertia is constrained by measuring the variations of the surface temperature for different local times. Methods. The surface temperature on the morning side of Steins is measured by inverting IR spectra between 4 and 5 microns acquired by the VIRTIS-M instrument onboard the Rosetta spacecraft. It is then compared to the theoretical temperatures obtained with a thermophysical model assuming either a smooth or rough surface. The heat conduction is computed radially into the first millimeters below the surface assuming a non-zero thermal inertia. The shape of the asteroid is reproduced by a 3D shape model composed of thousands of independent facets. We then compare both observed and computed temperatures within the footprint at different local times. Results. The observed temperatures are reproduced by a thermal inertia Γ = 110 ± 13 J m −2 K −1 s −1/2 for a smooth surface but some discrepancies remain between data and the thermal model at high incidence angles on the morning side near the terminator. This suggests that roughness that creates self-heating especially at low incidence angles is needed to reproduce all data. Surface roughness is modeled statistically. We assumed an infrared emissivity of 0.9 which corresponds to an effective emissivity IR eff = 0.73 ± 0.02 when combined with a small scale self heating parameter ξ = 0.2 derived from OSIRIS Hapke parameters. This is consistent with the emissivity of 0.6−0.7 measured by the microwave instrument MIRO at 0.53 mm. Surface temperature variations are then well reproduced with a thermal inertia of Γ = 210 ± 30 J m −2 K −1 s −1/2 . This value is higher than the one found for main-belt asteroids, but is consistent with kilometer-sized objects such as the near-Earth objects. It suggests a thin regolith layer and a low porosity.

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“…This model was used to study the creation of asteroid families, as well as a study on asteroid Šteins by Jutzi et al (2010a), that revealed a preference for an monolithic interior of Šteins before the impact that formed the largest crater Benavidez et al 2012 Diamond transformed it into a rubble pile body that is seen today. …”

Section: Simulating Impacts On Rubble Pile Asteroidsmentioning

confidence: 99%

“…• The impact that formed the crater Diamond at the southern pole will have shattered the body even if it was monolithic before (Jutzi et al 2010a). …”

Section: šTeins As a Rubble Pile Asteroidmentioning

confidence: 99%

Hyper-Velocity Impacts on Rubble Pile Asteroids

Deller¹

2017

Springer Theses

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SummaryMost asteroids in the size range of approximately 100 m to 100 km are rubble piles, aggregates of rocky material held together mainly by gravitational forces, and only weak cohesion. They contain high macroporosities, indicating a large amount of void space in their interiors. How these voids are distributed is not yet known, as in-situ measurements are still outstanding.In this work, a model to create rubble pile asteroid simulants for use in SPH impact simulations is presented. Rubble pile asteroids are modelled as gravitational re-aggregating remnant fragments of a catastrophically disrupted parent body, which are represented by spherical pebbles. It is shown that this approach allows to explicitly follow the internal restructuring of rubble pile asteroids during impact events, while preserving the expected properties of the bulk asteroid as known from observations and experiments. The bulk behaviour of asteroid simulants, as characterized by the stability against disruption and fragment size distribution, follows the expected behaviour and is not sensitive to the exact distribution of voids in the interior structure, but rather to the void fraction as the amount of consolidated void space in between the constituent fragment pebbles. No exact a priory knowledge of the fragment size distribution inside the body is therefore needed to use this model in impact simulations.Modelling the behaviour of the large-scale rubble pile constituents during impact events is used as a tool to infer the internal structure of asteroids by linking surface features like hills or pits to the creation of sub-catastrophic craters.In this work, the small rubble pile asteroid (2867) Šteins is analysed. The flyby of the Rosetta spacecraft at Šteins has revealed several interesting features: the large crater Diamond close to the southern pole, a hill like feature almost opposite to the crater, and a catena of crater pits extending radially from the rim of the crater.A possible link between these two structures and the cratering event is investigated in a series of impact simulations varying the interior of a plausible shape of Šteins prior to the event that formed crater Diamond. A connection between the cratering event and the hill is shown to be highly unlikely. Therefore, the hill is most likely a remnant of the formation of Šteins. Its size therefore helps to infer the initial size distribution of fragments forming the asteroid.The formation of a fracture radially from the crater can be observed for rubble pile simulants with highly collimated voids. This fracture could plausibly form the catena of pits observed on Šteins. This can therefore serve as a link between observable surface features and Šteins internal structure. The interior of Šteins is most likely an aggregate of fragments that themselves are only lightly fractured, and large void spaces might be found inside the asteroid. As Šteins seems to be a good example of a YORPoid, an asteroid that has been evolved to a top-like shape by radiative forces due to the YORP ...

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A large crater as a probe of the internal structure of the E-type asteroid Steins

Cited by 17 publications

References 17 publications

The large crater on the small Asteroid (2867) Steins

The large crater on the small Asteroid (2867) Steins

Thermal properties of the asteroid (2867) Steins as observed by VIRTIS/Rosetta

Hyper-Velocity Impacts on Rubble Pile Asteroids

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