TY - JOUR
T1 - (216) Kleopatra, a low density critically rotating M-type asteroid
AU - Marchis, F.
AU - Jorda, L.
AU - Vernazza, P.
AU - Broz, M.
AU - Hanuš, J.
AU - Ferrais, M.
AU - Vachier, F.
AU - Rambaux, N.
AU - Marsset, M.
AU - Viikinkoski, M.
AU - Jehin, E.
AU - Benseguane, S.
AU - Podlewska-Gaca, E.
AU - Carry, B.
AU - Drouard, A.
AU - Fauvaud, S.
AU - Birlan, M.
AU - Berthier, J.
AU - Bartczak, P.
AU - Dumas, C.
AU - Dudziński, G.
AU - Durech, J.
AU - Castillo-Rogez, J.
AU - Cipriani, F.
AU - Colas, F.
AU - Fetick, R.
AU - Fusco, T.
AU - Grice, J.
AU - Kryszczynska, A.
AU - Lamy, P.
AU - Marciniak, A.
AU - Michalowski, T.
AU - Michel, P.
AU - Pajuelo, M.
AU - Santana-Ros, T.
AU - Tanga, P.
AU - Vigan, A.
AU - Witasse, O.
AU - Yang, B.
N1 - Publisher Copyright:
©2021 ESO.
PY - 2021/9/1
Y1 - 2021/9/1
N2 - Context. The recent estimates of the 3D shape of the M/Xe-type triple asteroid system (216) Kleopatra indicated a density of ∼5 g cm-3, which is by far the highest for a small Solar System body. Such a high density implies a high metal content as well as a low porosity which is not easy to reconcile with its peculiar "dumbbell"shape. Aims. Given the unprecedented angular resolution of the VLT/SPHERE/ZIMPOL camera, here, we aim to constrain the mass (via the characterization of the orbits of the moons) and the shape of (216) Kleopatra with high accuracy, hence its density. Methods. We combined our new VLT/SPHERE observations of (216) Kleopatra recorded during two apparitions in 2017 and 2018 with archival data from the W. M. Keck Observatory, as well as lightcurve, occultation, and delay-Doppler images, to derive a model of its 3D shape using two different algorithms (ADAM, MPCD). Furthermore, an N-body dynamical model allowed us to retrieve the orbital elements of the two moons as explained in the accompanying paper. Results. The shape of (216) Kleopatra is very close to an equilibrium dumbbell figure with two lobes and a thick neck. Its volume equivalent diameter (118.75 ± 1.40) km and mass (2.97 ± 0.32) × 1018 kg (i.e., 56% lower than previously reported) imply a bulk density of (3.38 ± 0.50) g cm-3. Such a low density for a supposedly metal-rich body indicates a substantial porosity within the primary. This porous structure along with its near equilibrium shape is compatible with a formation scenario including a giant impact followed by reaccumulation. (216) Kleopatra's current rotation period and dumbbell shape imply that it is in a critically rotating state. The low effective gravity along the equator of the body, together with the equatorial orbits of the moons and possibly rubble-pile structure, opens the possibility that the moons formed via mass shedding. Conclusions. (216) Kleopatra is a puzzling multiple system due to the unique characteristics of the primary. This system certainly deserves particular attention in the future, with the Extremely Large Telescopes and possibly a dedicated space mission, to decipher its entire formation history.
AB - Context. The recent estimates of the 3D shape of the M/Xe-type triple asteroid system (216) Kleopatra indicated a density of ∼5 g cm-3, which is by far the highest for a small Solar System body. Such a high density implies a high metal content as well as a low porosity which is not easy to reconcile with its peculiar "dumbbell"shape. Aims. Given the unprecedented angular resolution of the VLT/SPHERE/ZIMPOL camera, here, we aim to constrain the mass (via the characterization of the orbits of the moons) and the shape of (216) Kleopatra with high accuracy, hence its density. Methods. We combined our new VLT/SPHERE observations of (216) Kleopatra recorded during two apparitions in 2017 and 2018 with archival data from the W. M. Keck Observatory, as well as lightcurve, occultation, and delay-Doppler images, to derive a model of its 3D shape using two different algorithms (ADAM, MPCD). Furthermore, an N-body dynamical model allowed us to retrieve the orbital elements of the two moons as explained in the accompanying paper. Results. The shape of (216) Kleopatra is very close to an equilibrium dumbbell figure with two lobes and a thick neck. Its volume equivalent diameter (118.75 ± 1.40) km and mass (2.97 ± 0.32) × 1018 kg (i.e., 56% lower than previously reported) imply a bulk density of (3.38 ± 0.50) g cm-3. Such a low density for a supposedly metal-rich body indicates a substantial porosity within the primary. This porous structure along with its near equilibrium shape is compatible with a formation scenario including a giant impact followed by reaccumulation. (216) Kleopatra's current rotation period and dumbbell shape imply that it is in a critically rotating state. The low effective gravity along the equator of the body, together with the equatorial orbits of the moons and possibly rubble-pile structure, opens the possibility that the moons formed via mass shedding. Conclusions. (216) Kleopatra is a puzzling multiple system due to the unique characteristics of the primary. This system certainly deserves particular attention in the future, with the Extremely Large Telescopes and possibly a dedicated space mission, to decipher its entire formation history.
KW - Minor planets, asteroids: individual: 216 Kleopatra
KW - Techniques: high angular resolution
UR - http://www.scopus.com/inward/record.url?scp=85114767929&partnerID=8YFLogxK
U2 - 10.1051/0004-6361/202140874
DO - 10.1051/0004-6361/202140874
M3 - Article
AN - SCOPUS:85114767929
SN - 0004-6361
VL - 653
JO - Astronomy and Astrophysics
JF - Astronomy and Astrophysics
M1 - A57
ER -