 Early estimates of nucleus 2I/Borisov diameter have ranged from .2I/Borisov has, unlike Solar System comets, noticeably shrunk during Solar System flyby, losing at least 0.4% of its mass before perihelion.Also, the amplitude of non-gravitational acceleration place an upper limit of 0.4 km on nucleus size, consistent with a previous Hubble Space Telescope upper limit of 0.5 km.