Spitzer Observations Of The Ultrafast-Rotator (54509) 2000 PH5

Abstract

We report preliminary results of Spitzer observations of the ultra-fast rotating (P~12 min) small (D~150 m) near-Earth asteroid (54509) 2000 PH5. We sampled its lightcurve at three thermal wavelengths with a temporal resolution of some ten seconds per data point. We employed a preliminary model of our target’s shape and spin state (courtesy of P.A. Taylor and J.-L Margot) and a detailed thermophysical model to determine its size, albedo, and thermal inertia. From knowledge of the thermal inertia, conclusions can be drawn on the presence or absence of loose material (regolith) on the asteroid surface. We expect our target to be regolith-free since its gravity cannot match the centrifugal force. Thermal inertia is also a key parameter in the determination of the Yarkovsky and YORP effects, two non-gravitational effects that affect the orbits and spin states of small asteroids. Vokrouhlický et al. (2005) have proposed that the Yarkovsky effect could be observable in the case of 2000 PH5.