Comets ... Halley as Jupiter

29 Mar 2012

At ... is Comet Wild2 subject to space weathering, is the question being asked, but it is a reference to a rusty red colouration on its surface. Microfocus Spectroscopy has shown Wild2 has been bombarded by particles in the solar wind and by micrometeorites for a long time, depositing grains of iron and reddening the surface (or that is the current thinking).

More important, at ... Jupiter played a role in Halley's comet and its spectacular meteor displays. Earth twice a year crosses the path of Halley's comet and dust particles and meteoroids burn up in the atmosphere during the process - the Orionids in October and the Eta Aquarids in May. The Orionids appear to be in resonant orbit with that of Jupiter and Halley's comet, it seems, has in the past been in resonant orbit with Jupiter - otherwise its debris, the Orionids, would not be. An astronomer from Armagh Observatory has modelled the orbit of Halley over 12000 years into the past and has suggested that from 1404 to 690BC Halley was trapped in a 1:6 resonance with Jupiter (in which Halley completed one orbit for every six orbits of Jupiter around the Sun). Later, from 240BC to 1700AD the orbit was in 2:13 resonance with Jupiter - but interestingly, the Orionid display of 1993, which is described as spectacular, had its origins in the event of 240BC when we have the first definite reference to Halley's comet.