10 Oct 2017

This one is going to get better - may be. The K2 comet (otherwise PANSTARRS comet) is currently beyond the orbit of Saturn but is heading towards the Sun. Even at that distance the comet has developed an 80,000 mile wide fuzzy cloud of dust (a coma) containing frozen gases. Se https://phys.org/print426436355.html ...

  ... the mainstream view is that sunlight is heating up frozen volatile gases that coat the comet's surface - and the coma is formed when these gas volatiles lift off from the comet and release dust (but see Tim Cullen's view on comets posted a short while ago). Most comets aren't very active until they approach at least the vicinity of Jupiter - so K2 is unusual in that respect. It is also unusual has it has not yet sported a tail - but its coma is very prominent. Comet tails of course are the result of the solar wind - and the comet is a long way off as yet.