Direct Detections of the Asteroidal YORP Effect

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The YORP effect is a torque that can modify the rotation rates and spin-axis orientations of small asteroids in the solar system. YORP torques are caused by the combined effects of incident solar radiation pressure and the recoil effect from anisotropic emission of thermal photons.

Several observed phenomena in asteroidal science indicate that such a torque acts upon the surfaces of asteroids and meteoroids, for which the YORP effect is the only realistic mechanism. Despite its importance, there existed only indirect evidence for the presence of YORP on solar system objects, until recently. The first direct detection of the YORP effect was achieved by Prof. Lowry and colleagues, by conducting optical and radar observational campaigns over 4 years on the small near-Earth asteroid, (54509) 2000 PH5 (Lowry et al., 2007, Science 316, 272-274; Taylor et al., 2007, Science 316, 274-277). Since then, the effect has been observed on just a few other asteroids due to the difficulties encountered in making such detections.

Prof. Lowry leads an on-going observational programme which makes use of telescope facilities at the European Southern Observatory (ESO), particularly the 8.2m VLT and the 3.5 NTT facilities. Other facilities include the 5m Hale Telescope at Palomar Observatory (California, USA), the 2m Robotic Liverpool Telescope (La Palma, Spain), the 2.5m Isaac Newton Telescope (La Palma, Spain), among many others. We use these telescopes to obtain optical photometric lightcurves, which can be used to construct convex 3-D shape models and spin-state solutions for these bodies. This programme is designed to survey a large sample of small Near-Earth Asteroids (NEAs) at to detect the YORP effect acting on these bodies, and to determine their likely surface compositions. Thermal-IR observations are also taken for detailed thermal analyses of their surfaces, important for constraining theoretical determinations of the strength of the YORP effect acting on our target NEAs. This programme is a collaboration with colleagues from the Open University, Queen’s University Belfast, Max Planck Institute for Solar System Research (Germany), NASA’s Jet Propulsion Laboratory (California, USA), and the Planetary Science Institute (Arizona, USA).

The YORP Effect has a major influence on the dynamical and physical properties of small asteroids and could lead to the formation of binary systems. In this example YORP has caused asteroid Ryugu to morph into a more regular ‘spinning-top’ shape. [Image Credit: Asteroid Ryugu from the JAXA Hayabusa 2 mission, 2018]

The student will assume a major role in the overall analysis and scientific interpretation of the full optical and thermal-IR data sets (CCD imaging and spectroscopy) as well as participating in several observing trips to the ESO telescope facilities in Chile, and other international facilities
(for MSc projects this would depend on available funding).

For more information please contact Prof. Stephen Lowry.