The unique inner-belt asteroid 311P/PANSTARRS ( formerly P/2013 P5 ) is notable for its sporadic , comet-like ejection of dust in nine distinct epochs spread over \sim 250 days in 2013 . This curious behavior has been interpreted as the product of localized , equator-ward landsliding from the surface of an asteroid rotating at the brink of instability . We obtained new Hubble Space Telescope observations to directly measure the nucleus and to search for evidence of its rapid rotation . We find a nucleus with mid-light absolute magnitude H _ { V } = 19.14 \pm 0.02 , corresponding to an equal-area circle with radius 190 \pm 30 m ( assuming geometric albedo p _ { V } = 0.29 ) . However , instead of providing photometric evidence for rapid nucleus rotation , our data set a lower limit to the lightcurve period , P \geq 5.4 hour . The dominant feature of the lightcurve is a V-shaped minimum , \sim 0.3 magnitudes deep , that is suggestive of an eclipsing binary . Under this interpretation , the time-series data are consistent with a secondary/primary mass ratio , m _ { s } / m _ { p } \sim 1:6 , a ratio of separation/primary radius , r / r _ { p } \sim 4 and an orbit period \sim 0.8 days . These properties lie within the range of other asteroid binaries that are thought to be formed by rotational breakup . While the lightcurve period is long , centripetal dust ejection is still possible if one or both components rotates rapidly ( \lesssim 2 hour ) and has a small lightcurve variation because of azimuthal symmetry . Indeed , radar observations of asteroids in critical rotation reveal “ muffin-shaped ” morphologies which are closely azimuthally symmetric and which show minimal lightcurves . Our data are consistent with 311P being a close binary in which one or both components rotates near the centripetal limit . The mass loss in 2013 suggests that breakup occurred recently and could even be on-going . A search for fragments that might have been recently ejected beyond the Hill sphere reveals none larger than effective radius r _ { e } \sim 10 m .