MPEC 2020-A113 :
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M.P.E.C. 2020-A113 Issued 2020 January 10, 21:11 UT The Minor Planet Electronic Circulars contain information on unusual minor planets and routine data on comets. They are published on behalf of Division F of the International Astronomical Union by the Minor Planet Center, Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A. Prepared using the Tamkin Foundation Computer Network MPC@CFA.HARVARD.EDU URL https://www.minorplanetcenter.net/ ISSN 1523-6714 S/2018 (3548) 1 K. S. Noll, NASA Goddard Space Flight Center; M. E. Brown, Caltech; H. A. Weaver, Johns Hopkins Applied Physics Lab; W. M. Grundy, Lowell Observatory; H. F. Levison, C. Olkin, S. B. Porter, M. W. Buie, J. R. Spencer, S. Marchi, Southwest Research Institute; and T. Statler, NASA Headquarters, report the detection of a satellite of the Trojan asteroid (3548) Eurybates. The satellite was detected with the Hubble Space Telescope's Wide Field Camera 3 (WFC3) at three separate epochs: 09:45 (UTC) 12 Sep 2018, 09:26(UTC) 14 Sep 2018, and 07:31 (UTC) 03 Jan 2020. The images show a satellite at separations of 0".589 +/- 0".020, 0".500 +/- 0".020, and 0".580 +/- 0".020, respectively, corresponding to projected distances of 1961 +/- 67, 1675 +/- 67, and 2292 +/- 79 km. Position uncertainty is estimated as one half of a WFC3 pixel. The position angle of the satellite, relative to Eurybates, was 259.9 +/- 0.3, 263.3 +/- 0.3 and 224.4 +/- 0.3 degrees East of North. The satellite's brightness was V = 26.95 +/- 0.5 on 03 Jan; if the satellite has the same albedo as Eurybates, it would have an effective diameter of 0.8 +/- 0.2 km. Eurybates was also observed with WFC3 at 06:37 (UTC) 11 Dec 2019 and 22:35 (UTC) 21 Dec 2019, but the satellite was not detected, implying a separation less than ~ 0".4, where an object of the observed brightness would be lost in the PSF of the primary. The relative positions of the satellite, including the non-detections, are consistent with physically reasonable orbits, but existing constraints are insufficient to uniquely define an orbit. Minor Planet Center (C) Copyright 2020 MPC M.P.E.C. 2020-A113


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