At www.spaceweather.com … Comet ISON is getting brighter and brighter as we approach the end of November encounter with the Sun. Its tail now extends 8 million km behind the nucleus – 21 times the distance between the Earth and the Moon. Not as fantastic as some of the historical comets – but enough to get astronomers fairly excited.
So much dust and gas is spewing from the nucleus it is impossible to get a handle on what is going on – what caused the outburst. They suggest fresh veins of ice have opened up that are vapourising furiously. Yet, they didn't see any ice, as such, on the various comet missions. Why don't they just say they don't know?