Abstract
Abstract The Yarkovsky–O’Keefe–Radzievskii–Paddack (YORP) effect is a small thermal-radiation torque experienced by small asteroids, and is considered to be crucial in their physical and dynamical evolution. It is important to understand this effect by providing measurements of YORP for a range of asteroid types to facilitate the development of a theoretical framework. We are conducting a long-term observational study on a selection of near-Earth asteroids to support this. We focus here on (68346) 2001 KZ66, for which we obtained both optical and radar observations spanning a decade. This allowed us to perform a comprehensive analysis of the asteroid’s rotational evolution. Furthermore, radar observations from the Arecibo Observatory enabled us to generate a detailed shape model. We determined that (68346) is a retrograde rotator with its pole near the southern ecliptic pole, within a 15○ radius of longitude 170○ and latitude −85○. By combining our radar-derived shape model with the optical light curves, we developed a refined solution to fit all available data, which required a YORP strength of $(8.43\pm 0.69)\times 10^{-8} \rm ~rad ~d^{-2}$. (68346) has a distinct bifurcated shape comprising a large ellipsoidal component joined by a sharp neckline to a smaller non-ellipsoidal component. This object likely formed either from the gentle merging of a binary system or from the deformation of a rubble pile due to YORP spin-up. The shape exists in a stable configuration close to its minimum in topographic variation, where regolith is unlikely to migrate from areas of higher potential.
Highlights
The Yarkovsky–O’Keefe–Radzievskii–Paddack (YORP) effect is a gentle torque that small asteroids can experience due to the reflection and thermal emission of sunlight from their surfaces (Rubincam 2000)
By combining our radar-derived shape model with the optical light curves, we developed a refined solution to fit all available data, which required a YORP strength of (8.43 ± 0.69) × 10−8 rad d−2. (68346) has a distinct bifurcated shape comprising a large ellipsoidal component joined by a sharp neckline to a smaller non-ellipsoidal component
KZ66 has a distinct bifurcated shape comprising a large ellipsoidal component joined by a sharp concavity to a smaller non-ellipsoidal curved component
Summary
YORP should produce both spin-up and spin-down cases. While recent theoretical developments are being proposed to explain the apparent lack of spin-down cases (Golubov & Krugly 2012; Golubov, Scheeres & Krugly 2014; Golubov 2017), to fully understand this important process requires more observational detections of the YORP effect in action. We are conducting a long-term monitoring campaign of a sample of near-Earth asteroids (NEAs) with the aim of detecting the signature of YORP through ongoing minute changes in their rotation periods. This programme began in 2010 April as part of an approved Large Programme at the European Southern Observatory (ESO LP). Many of our samples have been observed with planetary radar (Rozek et al 2019a, b) This allows for a more detailed shape model to be obtained, which greatly improves the likelihood of detecting YORP from the optical light-curve data and further improves the quality of the thermophysical modelling.
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