Scaling forces to asteroid surfaces: The role of cohesion

Scheeres, Daniel J.; Hartzell, C. M.; Sánchez, Paul; Swift, Michael

doi:10.1016/j.icarus.2010.07.009

Cited by 282 publications

(274 citation statements)

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“…xc, xc, sr, lr (21) where f is again some (in general different) range-separating function, and we replaced the screened dipole potential in the long-range part with the bare dipole potential, since it is assumed that the range of the exchange-correlation kernel is shorter than that of the range-separating function f. This separation splits the n-th term in the Dyson equation into 2 n terms, each of which is formed by some particular combination of T sr and T lr . Now we contract all the short-range segments ...α 0 T sr α 0 ... contained in these terms and introduce an effective short-range screened polarizability α sr (r, r′) such that the Dyson equation becomes Here, only the long-range coupling is considered explicitly via T lr , whereas the short-range coupling enters implicitly in the effective short-range screened polarizability α sr .…”

Section: Exact Correlation Energy From the Nonlocal Dynamic Polarizabmentioning

confidence: 99%

First-Principles Models for van der Waals Interactions in Molecules and Materials: Concepts, Theory, and Applications

2017

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Noncovalent van der Waals (vdW) or dispersion forces are ubiquitous in nature and influence the structure, stability, dynamics, and function of molecules and materials throughout chemistry, biology, physics, and materials science. These forces are quantum mechanical in origin and arise from electrostatic interactions between fluctuations in the electronic charge density. Here, we explore the conceptual and mathematical ingredients required for an exact treatment of vdW interactions, and present a systematic and unified framework for classifying the current first-principles vdW methods based on the adiabatic-connection fluctuation−dissipation (ACFD) theorem (namely the Rutgers−Chalmers vdW-DF, Vydrov−Van Voorhis (VV), exchange-hole dipole moment (XDM), Tkatchenko−Scheffler (TS), many-body dispersion (MBD), and random-phase approximation (RPA) approaches). Particular attention is paid to the intriguing nature of many-body vdW interactions, whose fundamental relevance has recently been highlighted in several landmark experiments. The performance of these models in predicting binding energetics as well as structural, electronic, and thermodynamic properties is connected with the theoretical concepts and provides a numerical summary of the state-of-the-art in the field. We conclude with a roadmap of the conceptual, methodological, practical, and numerical challenges that remain in obtaining a universally applicable and truly predictive vdW method for realistic molecular systems and materials.

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Section: Exact Correlation Energy From the Nonlocal Dynamic Polarizabmentioning

confidence: 99%

First-Principles Models for van der Waals Interactions in Molecules and Materials: Concepts, Theory, and Applications

2017

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“…This spinning-up selection process leaves behind the relatively fine-grained regolith with low thermal inertia that we see today 5 , and would work in addition to the thermal fatigue mechanism of asteroid regolith formation 22 .…”

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confidence: 99%

“…where g A is the ambient gravity and d is the grain diameter 5 . To prevent loss of surface material requires bond numbers of at least one, but surface stability requires the bond numbers to be greater than ten, which places limits on the possible grain sizes present.…”

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confidence: 99%

Cohesive forces prevent the rotational breakup of rubble-pile asteroid (29075) 1950 DA

Rozitis

MacLennan

Emery

2014

Nature

176

137

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Space missions 1 and ground-based observations 2 have shown that some asteroids are loose collections of rubble rather than solid bodies. The physical behavior of such 'rubble pile' asteroids has been traditionally described using only gravitational and frictional forces within a granular material 3 . Cohesive forces in the form of small van der Waals forces between constituent grains have been recently predicted to be important for small rubble piles (10-kilometer-sized or smaller), and can potentially explain fast rotation rates in the small asteroid population 4-6 . Hitherto, the strongest evidence came from an analysis of the rotational breakup of main belt comet P/2013 R3 (ref. 7), although that was indirect and poorly constrained by present observations. Here we report that the kilometer-sized asteroid (29075) 1950 DA 8 is a rubble pile that is rotating faster than that allowed by gravity and friction. We find that cohesive forces are required to prevent surface mass shedding and structural failure, and that the strength of the forces are comparable to, though somewhat less than, that of lunar regolith.It is possible to infer the existence of cohesive forces within an asteroid by determining if it is a rubble pile with insufficient self-gravity to prevent rotational breakup by centrifugal forces. One of the largest known candidates is near-Earth asteroid 1950 DA (mean diameter of 1.3 km; ref.8), as it has a rotation period of 2.1216 hr that is just beyond the critical spin limit of ~2.2 hr estimated for a cohesionless asteroid 9 . A rubble pile structure and the degree of self-gravity can be determined by a bulk density measurement, which can be acquired through model-tomeasurement comparisons of Yarkovsky orbital drift 10 . This drift arises on a rotating asteroid with non-zero thermal inertia, and is caused by the delayed thermal emission of absorbed sunlight, which applies a small propulsion force to the asteroid's afternoon side. Thermalinfrared observations can constrain the thermal inertia value 11 , and precise astrometric position measurements conducted over several years can constrain the degree of Yarkovsky orbital drift 2 . Recently, the orbital semimajor axis of 1950 DA has been observed to be decreasing at a rate of 44.1 ± 8.5 m yr -1 because of the Yarkovsky effect 12 , which indicates that the asteroid's sense of rotation must be retrograde. Using the Advanced Thermophysical Model 13,14 , in combination with the retrograde radar shape model 8 , archival WISE thermal-infrared data 15 (Extended Data Table 1, and Extended Data Figs 1 and 2), and orbital state 12 , we determine the thermal inertia and bulk density of 1950 DA (Methods). The thermal inertia value is found to be remarkably low at 24 +20 / -14 J m -2 K -1 s -1/2 , which gives a corresponding bulk density of 1.7 ± 0.7 g cm -3 ( Fig. 1 and Extended Data Fig. 3). This bulk density is much lower than the minimum value of 3.5 g cm -3 required to prevent loss of surface material by centrifugal forces (Fig. 2).Spectral observations of 1950...

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“…We plan to consider this possibility in more detail in a forthcoming paper. -The fractured material remains at the surface, possibly owing to either molecular sticking (Scheeres et al 2010) or an insufficiently interconnected system of fractures. This process leads to a gradual growth of the fractured volume near the surface, the physical and mechanical properties of which may be different from those of the core (interestingly, recent laboratory experiments have demonstrated that the thermal fatigue is able to disintegrate the surface of NEAs, producing a low-conductivity regolith layer, Delbo et al 2011).…”

Section: Resultsmentioning

confidence: 99%

“…Since we assume that the surface layer consists of particulate material, we neglect the effects of mechanical stresses in this part of the body. Two extreme approaches can then be adopted: (i) the surface layer is never removed from the body, assuming that the electrostatic and molecular sticking of its particles is able to resist either centrifugal or tidal effects (e.g., Scheeres et al 2010), and it only increases in size; or (ii) the surface layer, or its part, could be removed under some conditions by centrifugal or tidal accelerations. We deal with the first case and the second one is postponed to a forthcoming paper.…”

Section: Introductionmentioning

confidence: 99%

Thermal stresses in small meteoroids

Čapek

Vokrouhlický

2012

A&A

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Aims. We extend our previous analysis of thermal stresses in small, spherical and homogeneous meteoroids by taking into account the effects of a surface insulating layer. Methods. Using analytical computations, we determine the temperature distribution in a spherical inhomogeneous body smaller than ∼10 cm with a high-conductivity core and a low-conductivity surface layer. Our main approximation consists in (i) linearization of the surface energy-conservation constraint and (ii) omission of the seasonal effects in the Fourier spectrum of the incident solar radiation flux. Using the temperature solution, we analytically compute the mechanical (thermal) stress field in the core, neglecting its effects in the particulate surface layer. Conditions for material failure in the whole volume of the body are analyzed. In particular, we pay attention to whether the surface layer depth evolves toward an equilibrium situation. Results. As the meteoroid approaches the Sun, the thermal stress first exceeds the material strength at the surface of meteoroid. If the fractured material is able to stay on meteoroid, a particulate shell begins to form. After one revolution about the Sun, this process is roughly completed. We determine the dependence of its thickness on perihelion distance, spin axis orientation with respect to the Sun, and the size of meteoroid. We estimate the distribution of the final depths of the surface layer for eight major meteoroid showers with perihelion distances smaller than 1 AU.

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Scaling forces to asteroid surfaces: The role of cohesion

Cited by 282 publications

References 69 publications

First-Principles Models for van der Waals Interactions in Molecules and Materials: Concepts, Theory, and Applications

First-Principles Models for van der Waals Interactions in Molecules and Materials: Concepts, Theory, and Applications

Cohesive forces prevent the rotational breakup of rubble-pile asteroid (29075) 1950 DA

Thermal stresses in small meteoroids

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