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 m to 600 m, and loses dust at the peak rate 130 kg/s. The ejected dust has characteristic size 50 micron, is expelled sunward at 25 m/s, with a total ejected mass in the period of observation 1.5x10^9 kg. Mass loss from the fainter component, 240P-B, peaks at 35 kg/s and the total ejected mass was 2.3x10^8 kg. The radius of 240P-B is uncertain, with a best estimate about 300 m and an absolute lower limit 50 m. 240P-A and 240P-B are currently separating at about 1 m/s, a speed that is likely accelerating as a result of differential outgassing forces, and have a separation age over 3 years. 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.