Richardson, Derek C., Barnouin, Olivier S., Benner, Lance A. M., Bottke, William, Campo Bagatin, Adriano, Cheng, Andrew F., Eggl, Siegfried, Hamilton, Douglas P., Daniel HESTROFFER, Hirabayashi, Masatoshi, Maurel, Clara, Mcmahon, Jay W., Michel, Patrick, Murdoch, Naomi, Naidu, Shantanu P., Pravec, Petr, Rivkin, Andrew S., Rosenblatt, Pascal, Sarid, Gal, Scheeres, Daniel J., Scheirich, Peter, Tsiganis, Kleomenis, Zhang, Yun, Aida, Dynamical And Physical Properties Of Didymos Working Group, Department of Astronomy, University of Maryland, JHU/APL, Jet Propulsion Laboratory, California Institute of Technology (JPL), Southwest Research Inst, Universidad de Alicante, Institut de Mécanique Céleste et de Calcul des Ephémérides (IMCCE), Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Lille-Centre National de la Recherche Scientifique (CNRS), Planetology and Environments from Ground Astrometry and Space Exploration (PEGASE), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Lille-Centre National de la Recherche Scientifique (CNRS)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Department of Physics, Purdue University, Institut Supérieur de l'Aéronautique et de l'Espace (ISAE-SUPAERO), University of Colorado, Observatoire de la Côte d'Azur, COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA), Astronomical Institute, Observatoire Royal de Belgique (ORB), University of Central Florida, and Department of Physics, Aristotle University of Thessaloniki
International audience; Binary near-Earth asteroid (NEA) 65803 Didymos is the proposed Asteroid Impact & Deflection Assessment (AIDA) mission target, combining an orbiter [1] and a kinetic impactor for a planned encounter in fall 2022 [2]. The Dynamical and Physical Properties of Didymos Working Group supports this mission by addressing questions related to understanding the dynamical state of the system and inferring physical properties. Didymos is an Apollo-class NEA that likely reached its current orbit by exiting the inner main belt near or within the nu-6 resonance (> 82% chance) [3]. Remote observations [4] show Didymos is spectroscopically most consistent with ordinary chondrites. The diameters of the binary components are measured to be about 780 and 160 m [5]. A model of the short-term binary dynamics suggests possible librations of the secondary with up to ~10-deg amplitude, depending on its axial ratio. However, an equilibrium orbital and rotational solution is consistent with a libration amplitude of only ~1 deg. The primary, with an estimated 2.1 g/cc bulk density (uncertainty 30%) has a possibly super-critical rotation period of 2.26 h that may imply a cohesive strength of several tens of Pa. At this rate, perturbed regolith material may go through take-off/landing cycles and cause loss of fines due to solar radiation pressure. Based on a continuum analysis [6], the internal structure would likely fail before the equatorial region. A discrete analysis [7,8] shows that a minimum of 2.5 g/cc bulk density is needed for the structure to hold without cohesion. The system may be subject to weak thermal radiation forces (BYORP) with a period drift of no greater than 1 s/yr [9]. Experiments using the ISAE-SUPAERO drop tower [10] are underway to model the possible deployment of a lander on the secondary. References: [1] Michel et al. 2016, ASR 57, 2529; [2] Cheng et al. 2016, P&SS 127, 27; [3] Granvik et al. 2015, DPS 47, 214.07; [4] Dunn et al. 2013, LPSC 44, 1719; [5] Osip et al. 2016, this meeting; [6] Hirabayashi & Scheeres 2015, IAU 29, 2256185; [7] Barnouin et al. 2015, DPS 47, 402.09; [8] Zhang et al. 2016, this meeting; [9] McMahon et al. 2016, LPSC 47, 1903; [10] Sunday et al. 2016, Rev. Sci. Instr., accepted.