(Source NASA and STScI) - Comet ISON is potentially the “comet of the century” because around the time the comet makes its closest approach to the Sun, on November 28, it may briefly become brighter than the full Moon. Right now the comet is far below naked-eye visibility, and so Hubble was used to snap the view of the approaching comet, which is presently hurtling toward the Sun at approximately 47,000 miles per hour. When the Hubble picture was taken on April 10, the comet was slightly closer than Jupiter‘s orbit at a distance of 386 million miles from the Sun. Even at that great distance the Sun is warming the comet enough to trigger outgassing from its frozen gases locked up in the solid nucleus. Hubble photographed a jet blasting dust particles off the sunward-facing side of the comet’s nucleus. Preliminary measurements from the Hubble images suggest that the nucleus of ISON is no larger than three or four miles across. The comet was discovered in September 2012 by the Russian-led International Scientific Optical Network (ISON) using a 16-inch telesco
The image above is a contrast-enhanced image produced from the Hubble to reveal the subtle structure in the inner coma of the comet. In this computer-processed view, the Hubble image has been divided by a computer model coma that decreases in brightness proportionally to the distance from the nucleus, as expected for a comet that is producing dust uniformly over its surface. ISON’s coma shows enhanced dust particle release on the sunward-facing side of the comet’s nucleus, the small, solid body at the core of the comet. This information is invaluable for determining the comet’s shape, evolution, and spin of the solid nucleus.