Analytic theory for the tangential YORP produced by the asteroid regolith

Golubov, Oleksiy; Lipatova, V.

doi:10.1051/0004-6361/202243320

Cited by 3 publications

(3 citation statements)

References 19 publications

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“…The microscopic beaming effect of regolith grain-size-scale roughness (<1 mm) was shown -using the Hapke reflectance and emissivity model (Breiter & Vokrouhlickỳ 2011) -to have a marginal influence on the YORP effect. The transverse heat conduction across thermal skin depth (∼1 cm) causes an asymmetric thermal emission of the east and west sides of a boulder, giving rise to a systematic positive YORP torque (Golubov & Krugly 2012;Golubov & Lipatova 2022). The importance of the various self-modification effects of a concave feature on the surface was considered gradually and numerical approaches were taken to study it (Statler 2009;Rozitis & Green 2012, 2013a.…”

Section: Roughnessmentioning

confidence: 99%

“…However, accurately calculating the YORP effect on a real asteroid remains a challenge, as it has been demonstrated to be highly sensitive to surface topology (Statler 2009;Breiter et al 2009), such as uniform small-scale roughness (Rozitis & Green 2012), boulders (Golubov & Krugly 2012;Golubov et al 2014Golubov et al , 2021Ševeček et al 2015;Golubov 2017;Golubov & Scheeres 2019;Golubov & Lipatova 2022), and craters (Zhou et al 2022). Although the YORP torque caused by boulders and the tangential radiative force has been well studied, the YORP effect caused by concave structures has not yet been fully explored.…”

Section: Introductionmentioning

confidence: 99%

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A semi-analytical thermal model for craters with application to the crater-induced YORP effect

Zhou,

Michel

2024

A&A

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The YORP effect is the thermal torque generated by radiation from the surface of an asteroid. The effect is sensitive to surface topology, including small-scale roughness, boulders, and craters. The aim of this paper is to develop a computationally efficient semi-analytical model for the crater-induced YORP (CYORP) effect that can be used to investigate the functional dependence of this effect. This study linearizes the thermal radiation term as a function of the temperature in the boundary condition of the heat conductivity, and obtains the temperature field in a crater over a rotational period in the form of a Fourier series, accounting for the effects of self-sheltering, self-radiation, and self-scattering. By comparison with a numerical model, we find that this semi-analytical model for the CYORP effect works well for $K>0.1 W/m/K$. This semi-analytical model is computationally three-orders-of-magnitude more efficient than the numerical approach. We obtain the temperature field of a crater, accounting for the thermal inertia, crater shape, and crater location. We then find that the CYORP effect is negligible when the depth-to-diameter ratio is smaller than 0.05. In this case, it is reasonable to assume a convex shape for YORP calculations. Varying the thermal conductivity yields a consistent value of approximately 0.01 for the spin component of the CYORP coefficient, while the obliquity component is inversely related to thermal inertia, declining from 0.004 in basalt to 0.001 in metal. The CYORP spin component peaks at an obliquity of $0^ or $180^ while the obliquity component peaks at an obliquity of around $45^ or $135^ For a z-axis symmetric shape, the CYORP spin component vanishes, while the obliquity component persists. Our model confirms that the total YORP torque is damped by a few tens of percent by uniformly distributed small-scale surface roughness. Furthermore, for the first time, we calculate the change in the YORP torque at each impact on the surface of an asteroid explicitly and compute the resulting stochastic spin evolution more precisely. This study shows that the CYORP effect due to small-scale surface roughness and impact craters is significant during the history of asteroids. The semi-analytical method that we developed, which benefits from fast computation, offers new perspectives for future investigations of the YORP modeling of real asteroids and for the complete rotational and orbital evolution of asteroids accounting for collisions. Future research employing our CYORP model may explore the implications of space-varying roughness distribution, roughness in binary systems, and the development of a comprehensive rotational evolution model for asteroid groups.

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Section: Roughnessmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

A semi-analytical thermal model for craters with application to the crater-induced YORP effect

Zhou,

Michel

2024

A&A

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“…The predicted υ model depends on (ii), however, which may represent a significant perturbation in specific cases (e.g., Statler 2009;Breiter et al 2009). The specific physical phenomena that were considered to quantitatively test the YORP-dependence on these hidden parameters had to do with the lateral heat conduction in small-scale surface irregularities (e.g., Golubov & Krugly 2012;Ševeček et al 2015;Golubov & Lipatova 2022), or with the anisotropy of the thermal emission ("thermal beaming") and mutual irradiation of the surface facets (e.g., Rozitis & Green 2012, 2013a. We did not evaluate the contribution of (ii) here, and leave this part to future studies of specific targets.…”

Section: Justification Of the Rotation Rate Change Using A Theoretica...mentioning

confidence: 99%

Secular change in the spin states of asteroids due to radiation and gravitation torques

Ďurech,

Vokrouhlický,

Pravec

et al. 2024

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The rotation state of small asteroids is affected in the long term by perturbing torques of gravitational and radiative origin (the YORP effect). The former can be detected by a change in the spin-axis orientation in the inertial space; the latter manifests itself by a quadratic increase in the rotation phase. Direct observational evidence of the YORP effect is the primary goal of our work. This includes both the YORP detection for new objects and an improvement in the accuracy of previously known detections. We carried out photometric observations of five near-Earth asteroids: (1862) Apollo, (2100) Ra-Shalom, (85989) 1999 JD6, (138852) 2000 WN10, and (161989) Cacus. Then we applied the light-curve inversion method to all available data to determine the spin state and a convex shape model for each of the five studied asteroids. The YORP effect was modeled as a linear change of the rotation frequency $ In the case of (2100) Ra-Shalom, the analysis required that the spin-axis precession due to the solar gravitational torque also be included. We obtained two new detections of the YORP effect: (i) $ for (2100) Ra-Shalom, and (ii) $ for (138852) 2000 WN10. The analysis of Ra-Shalom also reveals a precession of the spin axis with a precession constant $ $. This is the first such detection from Earth-bound photometric data. For the other two asteroids, we improved the accuracy of the previously reported YORP detection: (i) $ for (1862) Apollo, and (ii) $ for (161989) Cacus. With this value, Apollo has the most precisely determined YORP effect so far. Despite the recent report of a detected YORP effect for (85989) 1999 JD6, we show that the model without YORP cannot be rejected statistically. Therefore, the detection of the YORP effect for this asteroid requires future observations. In several of our targets the currently available observations do not provide enough constraints on the shape model (even at large scales) to compute the theoretical YORP effect with sufficient precision. Nevertheless, the interpretation of the detected signal as the YORP effect is fairly plausible. The spin-axis precession constant of Ra-Shalom determined from observations matches the theoretically expected value. The total number of asteroids with a YORP detection has increased to 12. In all cases, the rotation frequency increases in time. The analysis of a rich photometric data set of irregularly shaped asteroids may require inclusion of spin-axis precession in future studies.

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The crater-induced YORP effect

Zhou

Zhang

Yan

et al. 2022

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Context. The Yarkovsky−O'Keefe−Radzievskii−Paddack (YORP) effect plays an important role in the rotational properties and evolution of asteroids. While the YORP effect induced by the macroscopic shape of the asteroid and by the presence of surface boulders has been well studied, no investigation has been performed yet regarding how craters with given properties influence this effect. Aims. We introduce and estimate the crater-induced YORP effect (CYORP), which arises from the concave structure of the crater, to investigate the magnitude of the resulting torques as a function of varying properties of the crater and the asteroid by a semi-analytical method. Methods. By using a simple spherical shape model of the crater and assuming zero thermal inertia, we calculated the total YORP torque due to the crater, which was averaged over the spin and orbital motions of the asteroid, accounting for self-sheltering and self-sheltering effects.Results. The general form of the CYORP torque can be expressed in terms of the crater radius R 0 and the asteroid radius R ast :, where W is an efficiency factor. We find that the typical values of W are about 0.04 and 0.025 for the spin and obliquity component, respectively, which indicates that the CYORP can be comparable to the normal YORP torque when the size of the crater is about one-tenth of the size of the asteroid, or equivalently when the crater/roughness covers one-tenth of the asteroid surface. Although the torque decreases with the crater size R 0 as ∼ R 2 0 , the combined contribution of all small craters can become non-negligible due to their large number when the commonly used power-law crater size distribution is considered. The CYORP torque of small concave structures, usually considered as surface roughness, is essential to the accurate calculation of the complete YORP torque. Under the CYORP effect that is produced by collisions, asteroids go through a random walk in spin rate and obliquity, with a YORP reset timescale typically of 0.4 Myr. This has strong implications for the rotational evolution and orbital evolution of asteroids.Conclusions. Craters and roughness on asteroid surfaces, which correspond to concave structures, can influence the YORP torques and therefore the rotational properties and evolution of asteroids. We suggest that the CYORP effect should be considered in the future investigation of the YORP effect on asteroids.

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Analytic theory for the tangential YORP produced by the asteroid regolith

Cited by 3 publications

References 19 publications

A semi-analytical thermal model for craters with application to the crater-induced YORP effect

A semi-analytical thermal model for craters with application to the crater-induced YORP effect

Secular change in the spin states of asteroids due to radiation and gravitation torques

The crater-induced YORP effect

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