First glimpse of ‘comet of the century’: Hubble gets snaps ISON that astronomers hope will amaze the world
Even at its current distance, the comet is already active as sunlight warms the surface and causes frozen volatiles to sublimate. Comets become more active as they near the inner solar system, where the Sun’s heat evaporates their ices into jets of gases and dust.
LOAD OF BALONEY. They get brighter because they are electrically active.