  We describe the discovery of a satellite of the Trojan asteroid (3548)
Eurybates in images obtained with the Hubble Space Telescope. The satellite was
detected on three separate epochs, two in September 2018 and one in January
2020. The satellite has a brightness in all three epochs consistent with an
effective diameter of d2 =1.2+/-0.4 km. The projected separation from Eurybates
was s~1700-2300 km and varied in position, consistent with a large range of
possible orbits. Eurybates is a target of the Lucy Discovery mission and the
early detection of a satellite provides an opportunity for a significant
expansion of the scientific return from this encounter.
