Investigation of Split Comet 240P/NEAT

Abstract We present time-series observations of the split comet 240P/NEAT near perihelion, obtained using the Nordic Optical Telescope. The brighter component, 240P-A, has an estimated radius in the range 400–600 m, and loses dust at the peak rate 130 kg s −1 . The ejected dust has characteristic size ∼50 μ m, is expelled sunward at ∼25 m s −1 , with a total ejected mass in the period of observation ∼1.5 × 10 9 kg. Mass loss from the fainter component, 240P-B, peaks at ∼35 kg s −1 and the total ejected mass was 2.3 × 10 8 kg. The radius of 240P-B is uncertain, with a best estimate ∼300 m and an absolute lower limit 50 m. 240P-A and 240P-B are currently separating at about 1 m s −1 , a speed that is likely accelerating as a result of differential outgassing forces, and have a separation age of >3 yr. The splitting of 240P is incompatible with the action of tides, impact, and internal pressure build up. 240P fits a developing picture, in which small comets are destroyed by rotational instabilities triggered by outgassing torques, an explanation that can be tested in 240P by future observations.