YORP Effect on Asteroid 162173 Ryugu: Implications for the Dynamical History

Kanamaru, Masanori; Sasaki, Sho; Morota, Tomokatsu; Cho, Yuichiro; Tatsumi, Eri; Hirabayashi, Masatoshi; Hirata, Naru; Senshu, Hiroki; Shimaki, Y.; Sakatani, Naoya; Tanaka, Satoshi; Okada, T.; Usui, Tomohiro; Sugita, Seiji; Watanabe, S.

doi:10.1029/2021je006863

Cited by 8 publications

(5 citation statements)

References 68 publications

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“…Similar YORP differences for shape models of different (but very high) resolution have also been observed in simulations of asteroid Itokawa (Scheeres et al 2007). Ryugu's accelerations obtained by Kanamaru et al (2021) correspond to the non-dimensional torque τ ω of the normal YORP in the range from −0.00014 to −0.0021. The tangential YORP τ ω ≈ 0.01 derived from our model can surpass this value, causing a positive net acceleration despite the negative YORP produced by the asteroid shape asymmetry.…”

Section: Resultsmentioning

confidence: 93%

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Analytic theory for the tangential YORP produced by the asteroid regolith

Golubov

Lipatova

2022

A&A

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Context. The tangential YORP effect is a radiation pressure torque produced by asymmetric thermal emission by structures on the asteroid surface. Previous works considered these structures to be boulders of different shapes lying on the surface of the asteroid. Aims. We study the tangential YORP produced by the rough interface of the asteroid's regolith. Methods. We created an approximate analytic theory of heat conduction on a slightly non-flat sinusoidal surface. We analyzed the published data on the small-scale shape of the asteroid (162173) Ryugu and estimated its tangential YORP due to the surface roughness. Results. We derive an analytic formula that expresses the tangential YORP of a sinusoidal surface in terms of its geometric and thermal properties. The tangential YORP is highest at the thermal parameter on the order of unity and for shape irregularities on the order of the thermal wavelength. Application of this equation to Ryugu predicts a tangential YORP that is 5-70 times greater than its normal YORP effect. Conclusions. The contribution of the small-scale regolith roughness to the YORP effect of the asteroid can be comparable to the normal YORP and the tangential YORP produced by boulders. The same theory can describe the roughness of the asteroid boulders, thus adding a new term to the previously considered the tangential YORP created by boulders.

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Section: Resultsmentioning

confidence: 93%

“…( 34), we obtain the non-dimensional TYORP produced by the surface roughness on Ryugu equal to τ ≈ 0.01. Kanamaru et al (2021) uses the shape model of Ryugu revealed by Hayabusa2 to compute the normal YORP. The resulting acceleration is negative and lies in the range −0.42 × 10 −6 deg day −2 to −6.3 × 10 −6 deg day −2 .…”

Section: Resultsmentioning

confidence: 99%

Analytic theory for the tangential YORP produced by the asteroid regolith

Golubov

Lipatova

2022

A&A

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“…We performed thermophysical simulations using the AsteroidThermoPhysicalModels.jl library, one of the functionalities of the asteroid dynamical simulator Astroshaper (https://github.com/ Astroshaper). This package was originally developed to predict the YORP effect on asteroid 162173 Ryugu, a target asteroid of Japan's Hayabusa2 spacecraft (Kanamaru et al 2021). The thermophysical model, originally formulated for a single asteroid, has been generalized to include all relevant thermal effects in a binary system.…”

Section: Comparison With Numerical Simulationmentioning

confidence: 99%

The Yarkovsky Effect on the Long-term Evolution of Binary Asteroids

Zhou 周,

Vokrouhlický,

Kanamaru

et al. 2024

ApJL

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We explore the Yarkovsky effect on small binary asteroids. While significant attention has been given to the binary YORP effect, the Yarkovsky effect is often overlooked. We develop an analytical model for the binary Yarkovsky effect, considering both the Yarkovsky–Schach and planetary Yarkovsky components, and verify it against thermophysical numerical simulations. We find that the Yarkovsky force could change the mutual orbit when the asteroid’s spin period is unequal to the orbital period. Our analysis predicts new evolutionary paths for binaries. For a prograde asynchronous secondary, the Yarkovsky force will migrate the satellite toward the location of the synchronous orbit on ∼100 kyr timescales, which could be faster than other synchronization processes such as YORP and tides. For retrograde secondaries, the Yarkovsky force always migrates the secondary outward, which could produce asteroid pairs with opposite spin poles. Satellites spinning faster than the Roche limit orbit period (e.g., from ∼4 hr to ∼10 hr) will migrate inward until they disrupt, reshape, or form a contact binary. We also predict a short-lived equilibrium state for asynchronous secondaries where the Yarkovsky force is balanced by tides. We provide calculations of the Yarkovsky-induced drift rate for known asynchronous binaries. If the NASA DART impact broke Dimorphos from synchronous rotation, we predict that Dimorphos’s orbit will shrink by a ̇ ∼ 7 cm yr−1, which can be measured by the Hera mission. We also speculate that the Yarkovsky force may have synchronized the Dinkinesh–Selam system after a possible merger of Selam’s two lobes.

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“…Here parameters and the magnitude of the TYORP (e.g., the size distribution and the thermal parameter of boulders) follow the research performed on asteroid Itokawa (Ševeček et al 2015). The TYORP torque differs from one asteroid to the next because the morphology of asteroids differs (Kanamaru et al 2021). For the CYORP torque, other parameters apart from the obliquity were set to be constant as δ = ∆ = α = π/4 and R 0 /R ast = 1/3.…”

Section: Order Of Magnitudementioning

confidence: 99%

“…Recently, in situ observations by spacecraft provided highresolution images of asteroids and measurements of their physical properties (e.g., Hirata et al 2009;, which enabled investigating the YORP effect with a high-resolution shape model of the considered asteroid (Kanamaru et al 2021;Roberts et al 2021). With high-resolution images, the thermally induced torque of craters whose sizes are above the image resolutions can be well represented by the NYORP torque, but we still miss the consideration of small craters or concave structures that are below the image resolution.…”

Section: Calculation Of the Total Yorp Torquementioning

confidence: 99%

The crater-induced YORP effect

Zhou

Zhang

Yan

et al. 2022

A&A

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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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YORP Effect on Asteroid 162173 Ryugu: Implications for the Dynamical History

Cited by 8 publications

References 68 publications

Analytic theory for the tangential YORP produced by the asteroid regolith

Analytic theory for the tangential YORP produced by the asteroid regolith

The Yarkovsky Effect on the Long-term Evolution of Binary Asteroids

The crater-induced YORP effect

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