Video: Comet ISON First Images Seen By NASA's Deep Impact Spacecraft

Long-period comets like ISON are thought to arrive from the solar system’s Oort cloud, a giant spherical cloud of icy bodies surrounding our solar system so far away its outer edge is about a third of the way to the nearest star (other than our sun). Every once in a while, one of these loose conglomerations of ice, rock, dust and organic compounds is disturbed out of its established orbit in the Oort cloud by a passing star or the combined gravitational effects of the stars in the Milky Way galaxy. With these gravitational nudges, so begins a comet’s eons-long, arching plunge toward the inner solar system.

ISON was discovered on Sept. 21, 2012, by two Russian astronomers using the International Scientific Optical Network’s 16-inch (40-centimeter) telescope near Kislovodsk. NASA’s Near-Earth Object Program Office, based at JPL, has plotted its orbit and determined that the comet is more than likely making it first-ever sweep through the inner solar system. Having not come this way before means the comet’s pristine surface has a higher probability of being laden with volatile material just spoiling for some of the sun’s energy to heat it up and help it escape. With the exodus of these clean ices could come a boatload of dust, held in check since the beginnings of our solar system. This released gas and dust is what is seen on Earth as comprising a comet’s atmosphere (coma) and tail.

ISON will not be a threat to Earth – getting no closer to Earth than about 40 million miles on Dec. 26, 2013. But stargazers will have an opportunity to view the comet’s head and tail before and after its closest approach to the sun — if the comet doesn’t fade early or break up before reaching the sun.

Launched in January 2005, NASA’s Deep Impact spacecraft traveled about 268 million miles (431 million kilometers) to the vicinity of comet Tempel 1. On July 3, 2005, the spacecraft deployed an impactor that was essentially “run over” by the nucleus of Tempel 1 on July 4. Sixteen days after comet encounter, the Deep Impact team placed the spacecraft on a trajectory to fly past Earth in late December 2007. This extended mission of the Deep Impact spacecraft culminated in the successful flyby of comet Hartley 2 on Nov. 4, 2010. In January of 2012, the spacecraft performed, from a distance, an imaging campaign on comet C/2009 P1 (Garradd).

To date, Deep Impact has traveled about 4.39 billion miles (7.06 billion kilometers) in space.

JPL, a division of the California Institute of Technology in Pasadena, manages the Deep Impact mission for NASA’s Science Mission Directorate, Washington. The University of Maryland is the Principal Investigator institution for the mission. Deep Impact is part of the Discovery Program managed at NASA’s Marshall Space Flight Center in Huntsville, Ala. The spacecraft was built for NASA by Ball Aerospace & Technologies Corp., Boulder, Colo. For more information about Deep Impact, visit:http://solarsystem.nasa.gov/deepimpact .