KOALA: 3-D shape of asteroids from multi-data inversion B. Carry, M. Kaasalainen, W. J. Merline, J. D. Drummond, J. ˇ Durech, J. Berthier, and A. Conrad 1 European Space Astronomy Center, ESA, Madrid (Spain, benoit.carry@esa.int), 2 Tampere University of Technology, Tampere (Finland), 3 Southwest Reseach Institute, Boulder, CO (USA), 4 Starfire Optical Range, Kirtland AFB, NM (USA), 5 Charles University, Pragues (Czech Republic), 6 IMCCE, Paris Observatory, Paris (France), and 7 Max-Planck-Institut für Astronomie, Heidelberg (Germany). Abstract We describe our on-going observing program to deter- mine the physical properties of asteroids from ground- based facilities. We combine disk-resolved images from adaptive optics, optical lightcurves, and stellar occultations to put tighter constraints on the spin, 3-D shape, and size of asteroids. We will discuss the rel- evance of the determination of physical properties to help understand the asteroid population (e.g., density, composition, and non-gravitational forces). We will then briefly describe our multi-data inversion algo- rithm KOALA (Carry et al. 2010a, Kaasalainen 2011, see also Kaasalainen et al., same meeting), which al- lows the determination of certain physical properties of an asteroid from the combination of different tech- niques of observation. A comparison of results ob- tained with KOALA on asteroid (21) Lutetia, prior to the ESA Rosetta flyby, with the high spatial resolu- tion images returned from that flyby, will then be pre- sented, showing the high accuracy of KOALA inver- sion. Finally, we will describe our current develop- ment of the algorithm, and focus on examples of other asteroids currently being studied with KOALA. 1. Introduction Knowledge of certain observable physical properties of small bodies (e.g., size, spin, 3-D shape) have far- reaching implications in furthering our understanding of these objects, such as density, composition, internal structure, and the effects of non-gravitational forces. For instance, the distribution of spin axes of the larger asteroids (diameter larger than ∼100 km) on the ce- lestial sphere is not expected to be isotropic. Numer- ical hydrocode simulations have predicted a slight ex- cess in prograde rotators, due to the gas-pebble inter- action in the protoplanetary disk (Johansen & Lacerda 2010). Similarly, the spin state of small asteroids (di- ameter of a few kilometers) is dominated by the non- gravitational YORP effect (Kaasalainen et al. 2007). Statistical knowledge of spin coordinates, how they are distributed within and among asteroid families of different ages, will provide strong constraints on the effectiveness of YORP. Reconstruction of the 3-D shape (including the size) is required to estimate the volume of an asteroid, which in turn is used to derive its density, which is possibly the property most fundamental to our under- standing of an asteroid (Britt et al. 2002). Observa- tions of the surface of an asteroid, such as colours, spectra, or phase effects, can provide clues to the sur- face composition of the asteroid. This may or may not be related to the bulk composition of the body. Masses for asteroids can be determined from a space- craft flyby, from the orbital motion of a natural moon, or even from the perturbations of asteroids on other bodies, such as Mars. In most cases, however, the un- certainty in the density is dominated by the uncertainty in the volume, rather than the uncertainty in the mass (Merline et al. 2002). Precise reconstruction of the 3- D shape is therefore of high importance for all aster- oids for which a mass has been, or will be, estimated. From the accurate astrometry that will result from, for example, Gaia and PanSTARRS, about 150–200 mass estimates are expected in the near future (e.g., Mouret et al. 2007). 2. KOALA We have developped a multi-data inversion algorithm: Knitted Occultation, Adaptive-optics, and Lightcurve Analysis (KOALA), that makes simultaneous use of data from three distinct observation types to determine the physical properties of asteroids (Carry et al. 2010a, Kaasalainen 2011). KOALA takes advantage of the specificity of each observing mode: the direct mea- sure of the apparent size and shape of asteroids on the plane of the sky provided by the timings of stel- lar occultations and disk-resolved images, and the in- EPSC Abstracts Vol. 6, EPSC-DPS2011-490-1, 2011 EPSC-DPS Joint Meeting 2011 c  Author(s) 2011