Hubble captures Comet ISON

This NASA/ESA Hubble Space Telescope image of Comet (C/2012 S1) ISON was photographed on 10 April, when the comet was just within Jupiter’s orbit, at a distance of 386 million miles from the Sun (394 million miles from Earth).

Even at that great distance the comet is already active as sunlight warms the surface and causes frozen volatiles to sublimate. Preliminary measurements from the Hubble images suggest that the nucleus of ISON is no larger than three or four miles across – remarkably small considering the high level of activity that researchers have observed in the comet so far. Astronomers are using these images to measure the activity level of this comet and constrain the size of the nucleus, in order to predict the comet’s activity when it skims 700 000 miles above the sun’s roiling surface on 28 November 2013.

The comet’s dusty coma is approximately 3 100 miles across, or 1.2 times the width of Australia. A dust tail extends more than 57 000 miles, far beyond Hubble’s field of view.

ISON stands for International Scientific Optical Network, a group of observatories in ten countries who have organised to detect, monitor, and track objects in space. ISON is managed by the Keldysh Institute of Applied Mathematics, part of the Russian Academy of Sciences.