sandbank model

… observed on Earth, the “sandbank” model suggested that a comet was simply a cloud of meteoritic particles held together by its own gravity. Interplanetary gases were adsorbed on the surfaces of the dust grains and escaped when the comet came close to the Sun and the particles were heated.…

…advocated Lyttleton’s idea of a sandbank nucleus, simply a cloud of meteoritic material with adsorbed gases. The question would not be put definitively to rest until the first spacecraft encounters with Halley’s Comet in 1986.