Title
Binary asteroid population. 3. Secondary rotations and elongations
Date Issued
15 March 2016
Access level
open access
Resource Type
research article
Author(s)
Pravec P.
Scheirich P.
Kušnirák P.
Hornoch K.
Galád A.
Naidu S.P.
Pray D.P.
Világi J.
Gajdoš
Kornoš L.
Krugly Y.N.
Cooney W.R.
Gross J.
Terrell D.
Gaftonyuk N.
Pollock J.
Husárik M.
Chiorny V.
Stephens R.D.
Durkee R.
Reddy V.
Dyvig R.
Vraštil J.
Žižka J.
Mottola S.
Hellmich S.
Oey J.
Benishek V.
Kryszczyńska A.
Higgins D.
Ries J.
Marchis F.
Baek M.
Macomber B.
Inasaridze R.
Kvaratskhelia O.
Ayvazian V.
Rumyantsev V.
Masi G.
Lecacheux J.
Montaigut R.
Leroy A.
Brown P.
Krzeminski Z.
Molotov I.
Reichart D.
Haislip J.
LaCluyze A.
Abstract
We collected data on rotations and elongations of 46 secondaries of binary and triple systems among near-Earth, Mars-crossing and small main belt asteroids. 24 were found or are strongly suspected to be synchronous (in 1:1 spin-orbit resonance), and the other 22, generally on more distant and/or eccentric orbits, were found or are suggested to have asynchronous rotations. For 18 of the synchronous secondaries, we constrained their librational angles, finding that their long axes pointed to within 20° of the primary on most epochs. The observed anti-correlation of secondary synchroneity with orbital eccentricity and the limited librational angles agree with the theories by Ćuk and Nesvorný (Ćuk, M., Nesvorný, D. [2010]. Icarus 207, 732-743) and Naidu and Margot (Naidu, S.P., Margot, J.-L. [2015]. Astron. J. 149, 80). A reason for the asynchronous secondaries being on wider orbits than synchronous ones may be longer tidal circularization time scales at larger semi-major axes. The asynchronous secondaries show relatively fast spins; their rotation periods are typically <10 h. An intriguing observation is a paucity of chaotic secondary rotations; with an exception of (35107) 1991 VH, the secondary rotations are single-periodic with no signs of chaotic rotation and their periods are constant on timescales from weeks to years. The secondary equatorial elongations show an upper limit of a2/b2~1.5. The lack of synchronous secondaries with greater elongations appears consistent, considering uncertainties of the axis ratio estimates, with the theory by Ćuk and Nesvorný that predicts large regions of chaotic rotation in the phase space for a2/b2≳2. Alternatively, secondaries may not form or stay very elongated in gravitational (tidal) field of the primary. It could be due to the secondary fission mechanism suggested by Jacobson and Scheeres (Jacobson, S.A., Scheeres, D.J. [2011]. Icarus 214, 161-178), as its efficiency is correlated with the secondary elongation. Sharma (Sharma, I. [2014]. Icarus 229, 278-294) found that rubble-pile satellites with a2/b2≲1.5 are more stable to finite structural perturbations than more elongated ones. It appears that more elongated secondaries, if they originally formed in spin fission of parent asteroid, are less likely to survive intact and they more frequently fail or fission.
Start page
267
End page
295
Volume
267
Language
English
OCDE Knowledge area
Astronomía
Subjects
Scopus EID
2-s2.0-84952930541
Source
Icarus
ISSN of the container
00191035
Sponsor(s)
We thank to Alan Harris, Seth Jacobson, Michael Efroimsky, Matija Ćuk, Ishan Sharma and Masatoshi Hirabayashi for fruitful discussions on a number of things in this paper. The work at Ondřejov and observations with the Danish 1.54-m telescope on the ESO La Silla station were supported by the Grant Agency of the Czech Republic , Grants P209/12/0229 and 15-07193S . The work at Modra was supported by the Slovak Grant Agency for Science VEGA , Grant 1/0670/13 . Operations at Sugarloaf Mountain were supported by a Gene Shoemaker NEO grant from the Planetary Society. The work at Tatranská Lomnica was supported by the Slovak Grant Agency for Science VEGA , Grant 2/0032/14 and project ITMS No. 26220120009, based on the supporting operational Research and development program financed from the European Regional Development Fund . The work at SETI Institute was supported by NASA Grants NNX11AD62G and NNX14AJ80G . The work at Abastumani was supported by the Shota Rustaveli National Science Foundation , Grant FR/379/6-300/14 . We thank to S. Nudds for her contribution with observations from Elginfield Observatory, University of Western Ontario.
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