SODIUM TAILS OF COMETS: Na/O AND Na/Si ABUNDANCES IN INTERPLANETARY DUST PARTICLES

摘要

The average measured Na/O = 2.7 x 10~(-2) (atomic ratio) in chondritic interplanetary dust particles (IDPs) is an order of magnitude higher than the cosmic abundance, and Na/Si = 0.11 is about twice the cosmic value. These ratios are similar to those measured in the mixed and silicate dust particles ejected from the nucleus of comet Halley. The observations indicate that dust in a comet nucleus is the main repository of sodium and that cometary ices are mostly Na free. The measured Na/O value in Hale-Bopp's sodium tail is much less than 0.1 times the cosmic abundance, which is lower than the sodium abundance measured in cluster IDPs collected in the Earth's lower stratosphere.