posted on Nov, 21 2013 @ 02:47 AM
reply to post by cheesy
It is thought that the nucleus is around 3 miles (5Km) in diameter.
The reason the coma/tail are so big is all that sublimation of the ice has essentially formed an atmosphere around the comet, but the gravity on the
comet is so weak, it can extend out for quite some considerable distance.
It is also too weak to hold on to it, so the dust and gas escapes forming the tail.
There are actually two tails on a comet (usually), the plasma tail is the gases, ionised by UV photons from the sun, and then the solar wind carries
them away. The second tail is the dust tail, which can move in a slightly different direction to the plasma tail.
With no real forces in space, apart from the solar wind, these can extend for several hundreds of thousands of miles.
The "wings" on ISON btw, are likely large parts of it breaking off as it approaches the sun, hopefully it isn't a sign of a total break up.