The stratification of regolith on celestial objects

Schräpler, Rainer; Blum, Jürgen; Borstel, Ingo von; Güttler, C.

doi:10.1016/j.icarus.2015.04.033

Cited by 32 publications

(36 citation statements)

References 34 publications

(81 reference statements)

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“…Thus, the sinter neck can form in ice-rich areas at these temperatures, but the increase of the tensile and the compressive strength are only temporary. (Schräpler et al 2015), homogeneous dust layers (Güttler et al 2009) and homogeneous water-ice layers (Lorek et al 2016). Since all the samples start with a different initial volume filling factor, the compression curves were normalized to an initial and a maximum volume filling factor of 0.05 and 0.6, respectively.…”

Section: Strength From Laboratory Experimentsmentioning

confidence: 99%

The Thermal, Mechanical, Structural, and Dielectric Properties of Cometary Nuclei After Rosetta

et al. 2019

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The physical properties of cometary nuclei observed today relate to their complex history and help to constrain their formation and evolution. In this article, we review some of the main physical properties of cometary nuclei and focus in particular on the thermal, mechanical, structural and dielectric properties, emphasizing the progress made during the Rosetta mission. Comets have a low density of 480 ± 220 kg m -3 and a low permittivity of 1.9 -2.0, consistent with a high porosity of 70 -80 %, are weak with a very low global tensile strength <100 Pa, and have a low bulk thermal inertia of 0 -60 J K -1 m -2 s -1/2 that allowed them to preserve highly volatiles species (e.g. CO, CO2, CH4, N2) into their interior since their formation. As revealed by 67P/Churyumov-Gerasimenko, the above physical properties vary across the nucleus, spatially at its surface but also with depth. The broad picture is that the bulk of the nucleus consists of a weakly bonded, rather homogeneous material that preserved primordial properties under a thin shell of processed material, and possibly covered by a granular material; this cover might in places reach a thickness of several meters. The properties of the top layer (the first meter) are not representative of that of the bulk nucleus. More globally, strong nucleus heterogeneities at a scale of a few meters are ruled out on 67P's small lobe.

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Section: Strength From Laboratory Experimentsmentioning

confidence: 99%

The Thermal, Mechanical, Structural, and Dielectric Properties of Cometary Nuclei After Rosetta

et al. 2019

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“…Because of the higher specific surface energy of water ice, the rolling friction force of water ice is also enhanced in comparison to the silica dust particles, which implies that a higher pressure is required to rearrange the water ice particles in the samples. For a more detailed discussion of the compression physics of granular material, see Schräpler et al (2015).…”

Section: Laboratory Experiments On Dust and Ice Compressionmentioning

confidence: 99%

Comet formation in collapsing pebble clouds

Lorek

Gundlach

Lacerda

et al. 2016

A&A

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Context. Comets are remnants of the icy planetesimals that formed beyond the ice line in the solar nebula. Growing from μm-sized dust and ice particles to km-sized objects is, however, difficult because of growth barriers and time scale constraints. The gravitational collapse of pebble clouds that formed through the streaming instability may provide a suitable mechanism for comet formation. Aims. We study the collisional compression of silica, ice, and silica/ice-mixed pebbles during gravitational collapse of pebble clouds. Using the initial volume-filling factor and the dust-to-ice ratio of the pebbles as free parameters, we constrain the dust-to-ice mass ratio of the formed comet and the resulting volume-filling factor of the pebbles, depending on the cloud mass. Methods. We use the representative particle approach, which is a Monte Carlo method, to follow cloud collapse and collisional evolution of an ensemble of ice, silica, and silica/ice-mixed pebbles. Therefore, we developed a collision model which takes the various collision properties of dust and ice into account. We study pebbles with a compact size of 1 cm and vary the initial volume-filling factors, φ 0 , ranging from 0.001 to 0.4. We consider mixed pebbles as having dust-to-ice ratios between 0.5 and 10. We investigate four typical cloud masses, M, between 2.6 × 10 14 (very low) and 2.6 × 10 23 g (high). Results. Except for the very low-mass cloud (M = 2.6 × 10 14 g), silica pebbles are always compressed during the collapse and attain volume-filling factors in the range from φ V ≈ 0.22 to 0.43, regardless of φ 0 . Ice pebbles experience no significant compression in very low-mass clouds. They are compressed to values in the range φ V ≈ 0.11 to 0.17 in low-and intermediate-mass clouds (M = 2.6 × 10 17 −2.6 × 10 20 g); in high-mass clouds (M = 2.6 × 10 23 g), ice pebbles end up with φ V ≈ 0.23. Mixed pebbles obtain filling factors in between the values for pure ice and pure silica. We find that the observed cometary density of ∼0.5 g cm −3 can only be explained by either intermediate-or high-mass clouds, regardless of φ 0 , and also by either very low-or low-mass clouds for initially compact pebbles. In any case, the dust-to-ice ratio must be in the range of between 3 ξ 9 to match the observed bulk properties of comet nuclei.

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“…Thus, the thickness of the layer accumulated per time step is calculated by the mean amount of total ejecta of the 10 4 surface elements during 4.5 Gyrs, divided by the time span between two successive impacts. We assume that the redeposited regolith particles form a layer with a volume filling factor of φ = 0.6 (Schräpler et al 2015). 9: As in step 2, the one-dimensional element with the record of the previous impacts is extended into a two-dimensional array, with a width corresponding to the crater radius of the subsequent impact.…”

Section: The Monte Carlo Codementioning

confidence: 99%

“…9). Schräpler et al (2015) studied the packing density of a regolith layer under different gravity levels and found the volume filling factor to saturate at a value of 0.6 for thicknesses exceeding a few meters. This regolith layer shields the asteroid from a high degree of compaction on its surface.…”

Section: An Evolution Model For Asteroids and The Formation Of Meteormentioning

confidence: 99%

“…Such small bodies only recapture about 50 percent of the crater ejecta. The packing density of the regolith layer was recently studied by Schräpler et al (2015) and is mostly independent of the size of the parent body and for not too small grains independent of the regolith grain size. Typical volume filling factors are φ = 0.6, close to the limit of random close packing.…”

Section: Introductionmentioning

confidence: 99%

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The Collisional Evolution of Undifferentiated Asteroids and the Formation of Chondritic Meteoroids

Beitz

Blum

Parisi

et al. 2016

ApJ

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Most meteorites are fragments from recent collisions experienced in the asteroid belt. In such a hyper-velocity collision, the smaller collision partner is destroyed, whereas a crater on the asteroid is formed or it is entirely disrupted, too. The present size distribution of the asteroid belt suggests that an asteroid with 100 km radius is encountered 10 14 times during the lifetime of the Solar System by objects larger than 10 cm in radius; the formed craters cover the surface of the asteroid about 100 times. We present a Monte Carlo code that takes into account the statistical bombardment of individual infinitesimally small surface elements, the subsequent compaction of the underlying material, the formation of a crater and a regolith layer. For the entire asteroid, 10,000 individual surface elements are calculated. We compare the ejected material from the calculated craters with the shock stage of meteorites with low petrologic type and find that these most likely stem from smaller parent bodies that do not possess a significant regolith layer. For larger objects, which accrete a regolith layer, a prediction of the thickness depending on the largest visible crater can be made. Additionally, we compare the crater distribution of an object initially 100 km in radius with the shape model of the asteroid (21) Lutetia, assuming it to be initially formed spherical with a radius that is equal to its longest present ellipsoid length. Here, we find the shapes of both objects to show resemblance to each other.

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The stratification of regolith on celestial objects

Cited by 32 publications

References 34 publications

The Thermal, Mechanical, Structural, and Dielectric Properties of Cometary Nuclei After Rosetta

The Thermal, Mechanical, Structural, and Dielectric Properties of Cometary Nuclei After Rosetta

Comet formation in collapsing pebble clouds

The Collisional Evolution of Undifferentiated Asteroids and the Formation of Chondritic Meteoroids

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