Compact YORP formulation and stability analysis

Kaasalainen, M.; Nortunen, Hari

doi:10.1051/0004-6361/201322221

Cited by 9 publications

(9 citation statements)

References 18 publications

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“…Furthermore, the Geographos prediction is relatively insensitive to small-scale shape features, as when the roughness is allowed to vary in an extreme way across the surface it only introduced an uncertainty of ∼30%. Similar findings were made byĎurech et al (2008b) and Kaasalainen & Nortunen (2013). InĎurech et al (2008b), they added small-scale topography from the spacecraft-derived and high-resolution shape model of (25143) Itokawa (Gaskell 2008) to the light-curve shape model of Geographos and found no differences larger than ∼5% between their YORP rotational acceleration predictions.…”

Section: Modelling Critiquessupporting

confidence: 82%

Physical characterisation of near-Earth asteroid (1620) Geographos

Rozitis

Green

2014

A&A

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Context. The Yarkovsky (orbital drift) and YORP (spin state change) effects play important roles in the dynamical and physical evolution of asteroids. Thermophysical modelling of these observed effects, and of thermal-infrared observations, allows a detailed physical characterisation of an individual asteroid to be performed. Aims. We perform a detailed physical characterisation of near-Earth asteroid (1620) Geographos, a potential meteor stream source and former spacecraft target, using the same techniques as previously used for (1862) Apollo. Methods. We use the advanced thermophysical model (ATPM) on published light-curve, radar, and thermal-infrared observations to constrain the thermophysical properties of Geographos. The derived properties are used to make detailed predictions of the Yarkovsky orbital drift and YORP rotational acceleration, which are then compared against published measurements to determine Geographos's bulk density. Results. We find that Geographos has a thermal inertia of 340 +140 −100 J m −2 K −1 s −1/2 , a roughness fraction of ≥50%, and a bulk density of 2100 +550 −450 kg m −3 when using the light-curve-derived shape model with the radar-derived maximum equatorial diameter of 5.04 ± 0.07 km. It is also found that the radar observations had overestimated the z-axis in Geographos's shape model because of their near-equatorial view. This results in a poor fit to the thermal-infrared observations if its effective diameter is kept fixed in the model fitting.Conclusions. The thermal inertia derived for Geographos is slightly higher than the typical values for a near-Earth asteroid of its size, and its derived bulk density suggests a rubble-pile interior structure. Large uncertainties in shape model z-axes are likely to explain why radar and thermal-infrared observations sometimes give inconsistent diameter determinations for other asteroids.

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Section: Modelling Critiquessupporting

confidence: 82%

Physical characterisation of near-Earth asteroid (1620) Geographos

Rozitis

Green

2014

A&A

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“…Thus, even axisymmetric spheroids, which have zero spin torque, will have their axes reoriented by YORP, and will have their obliquities changed if they have finite thermal inertia Γ. These results have been derived analytically by Breiter et al (2007), Breiter and Michalska (2008), and Kaasalainen and Nortunen (2013), but seem to have been underappreciated, perhaps owing to the highly mathematical presentations in those papers.…”

Section: Yorp Evolution Of Symmetric and Nearly Symmetric Asteroidsmentioning

confidence: 99%

Obliquities of “top-shaped” asteroids may not imply reshaping by YORP spin-up

Statler

2015

Icarus

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The timescales over which the YORP effect alters the rotation period and the obliquity of a small asteroid can be very different, because the corresponding torques couple to different aspects of the object's shape. For nearly axisymmetric, "top-shaped" near-Earth asteroids such as 101955 Bennu, spin timescales are an order of magnitude or more longer than obliquity timescales, which are ∼ 10 5 to 10 6 yr. The observed low obliquities (near 0• or 180 • ) of top-shaped asteroids do not constitute evidence that they acquired their present shapes and spins through YORP spin-up, because low obliquities are expected regardless of the spin-up or reshaping mechanism.

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“…The non-dimensional coefficients A n and B n in Eqs. ( 4) and ( 5) are determined by the shape of the body, either analytically or semianalytically (e.g., Vokrouhlický, 2007, 2008a;Scheeres and Mirrahimi, 2008;Breiter and Michałska, 2008;Kaasalainen and Nortunen, 2013). Interestingly, analytical methods help to understand that torque component that changes the spin rate and the components that change the axis orientation couple, at leading order, to different attributes of the surface.…”

Section: Classical Modelsmentioning

confidence: 99%

“…If mutual shadowing of the surface facets is to be taken into account, one may use a semi-analytic approach mentioned by ; see already Scheeres and Mirrahimi (2008). Depending on details of the shape, the series in ( 4) and ( 5) may either converge quickly, with the first few terms dominating the overall behavior, or may slowly converge, with high-degree terms continuing to contribute (e.g., Vokrouhlický, 2007, 2008a;Kaasalainen and Nortunen, 2013).…”

Section: Classical Modelsmentioning

confidence: 99%

The Yarkovsky and YORP Effects

Vokrouhlicky,

Bottke,

Chesley

et al. 2015

Preprint

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The Yarkovsky effect describes a small but significant force that affects the orbital motion of meteoroids and asteroids smaller than 30 − 40 kilometers in diameter. It is caused by sunlight; when these bodies heat up in the Sun, they eventually re-radiate the energy away in the thermal waveband, which in turn creates a tiny thrust. This recoil acceleration is much weaker than solar and planetary gravitational forces, but it can produce measurable orbital changes over decades and substantial orbital effects over millions to billions of years. The same physical phenomenon also creates a thermal torque that, complemented by a torque produced by scattered sunlight, can modify the rotation rates and obliquities of small bodies as well. This rotational variant has been coined the Yarkovsky-O'Keefe-Radzievskii-Paddack (YORP) effect. During the past decade or so, the Yarkovsky and YORP effects have been used to explore and potentially resolve a number of unsolved mysteries in planetary science dealing with small bodies. Here we review the main results to date, and preview the goals for future work.

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Compact YORP formulation and stability analysis

Cited by 9 publications

References 18 publications

Physical characterisation of near-Earth asteroid (1620) Geographos

Physical characterisation of near-Earth asteroid (1620) Geographos

Obliquities of “top-shaped” asteroids may not imply reshaping by YORP spin-up

The Yarkovsky and YORP Effects

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