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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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