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A thermophysical analysis of the (1862) Apollo Yarkovsky and YORP effects

Rozitis, B.; Duddy, S. R.; Green, S. and Lowry, S. C. (2013). A thermophysical analysis of the (1862) Apollo Yarkovsky and YORP effects. Astronomy & Astrophysics, 555, article no. A20.

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Context. The Yarkovsky effect, which causes orbital drift, and the YORP effect, which causes changes in rotation rate and pole orientation, play important roles in the dynamical and physical evolution of asteroids. Near-Earth asteroid (1862) Apollo has strong detections of both orbital semimajor axis drift and rotational acceleration.

Aims. To produce a unified model that can accurately match both observed effects using a single set of thermophysical properties derived from ground-based observations, and to determine Apollo’s long term evolution.

Methods. We use light-curve shape inversion techniques and the Advanced Thermophysical Model (ATPM) on published light-curve, thermal-infrared, and radar observations to constrain Apollo’s thermophysical properties. The derived properties are used to make detailed predictions of Apollo’s Yarkovsky and YORP effects, which are then compared with published measurements of orbital drift and rotational acceleration. The ATPM explicitly incorporates 1D heat conduction, shadowing, multiple scattering of sunlight, global self-heating, and rough surface thermal-infrared beaming in the model predictions.

Results. We find that ATPM can accurately reproduce the light-curve, thermal-infrared, and radar observations of Apollo, and simultaneously match the observed orbital drift and rotational acceleration using: a shape model with axis ratios of 1.94:1.65:1.00, an effective diameter of 1.55 ± 0.07 km, a geometric albedo of 0.20 ± 0.02, a thermal inertia of 140 +140-100 J m-2 K-1 s-1/2, a highly rough surface, and a bulk density of 2850 +480-680 kg m-3. Using these properties we predict that Apollo’s obliquity is increasing towards the 180 degree YORP asymptotic state at a rate of 1.5 +0.3-0.5 degrees per 105 yr.

Conclusions. The derived thermal inertia suggests that Apollo has loose regolith material resting on its surface, which is consistent with Apollo undergoing a recent resurfacing event based on its observed Q-type spectrum. The inferred bulk density is consistent with those determined for other S-type asteroids, and suggests that Apollo has a fractured interior. The YORP effect is acting on a much faster timescale than the Yarkovsky effect and will dominate Apollo’s long term evolution. The ATPM can readily be applied to other asteroids with similar observational data sets.

Item Type: Journal Item
Copyright Holders: 2013 European Southern Observatory
ISSN: 1432-0746
Project Funding Details:
Funded Project NameProject IDFunding Body
Rolling Grant "Understanding Origins at the Open University" Project TST/1001964/1STFC (Science & Technology Facilities Council)
Keywords: thermal radiation mechanisms; data analysis; celestial mechanics; infrared planetary systems; minor planets; asteroids
Academic Unit/School: Faculty of Science, Technology, Engineering and Mathematics (STEM) > Physical Sciences
Faculty of Science, Technology, Engineering and Mathematics (STEM)
Item ID: 39546
Depositing User: Simon Green
Date Deposited: 24 Feb 2014 14:34
Last Modified: 10 Dec 2018 10:18
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