Comet ISON – An Icy Visitor Cometh
The above image was taken by UK astronomer Pete Lawrence on September 15 as Comet ISON passed through the constellation of Cancer en route to Leo. Lawrence used a 10 cm-diameter telescope with a CCD camera attached; the exposures totaled 40 minutes, with individual images stacked together to produce the final result.
Originating in the Oort Cloud, a repository of icy bodies billions of kilometers from the Sun, Comet ISON is on a path which will bring it within skimming distance, or about 730,000 miles above the Sun’s visible surface, on November 28. The comet was first discovered, and cataloged as C/2012 S1, in images taken September 21, 2012 by astronomers Artyom Novichonok and Vitali Nevski using a 40 cm-diameter telescope which is part of the International Scientific Optical Network (ISON).
The comet will be brightest in our skies just before, and in the week following, its encounter with the Sun making its closest approach to Earth on December 26 – assuming it survives! A comet’s journey through the Solar System is a violent and perilous one, to say the least. A giant ejection of solar material from the sun could rip its tail off. Before it reaches Mars, at some 230 million miles away from the Sun, the solar radiation begins to boil its water which is the first step toward breaking apart. Even surviving this, the intense radiation and pressure as it nears the Sun’s surface could destroy it altogether. If Comet ISON does come around the Sun without breaking up, it will be visible in the Northern Hemisphere with the naked eye – and from what observers are now seeing – ISON is promising to be a particularly bright and beautiful comet.
Astronomers are now watching as the comet draws closer, its coma – the tenuous atmosphere surrounding the comet’s rock–ice nucleus – is becoming more pronounced as its surface ices are heated by the Sun and transformed into gas. Dusty debris suspended in the coma and swept into a tail will also become more prominent as the comet draws nearer.
This is Comet ISON’s first trip around the Sun, meaning it is still made of pristine matter from the earliest days of our Solar System’s formation, its top layers never having been lost by a trip near the Sun. Scientists will be pointing as many ground-based observatories as they can, and at least 15 space-based assets, towards the comet along the way in order to learn more about this traveling time capsule.
NASA and European Space Agency (ESA) space missions are preparing to observe Comet ISON on its approach to the Sun. The ESA’s Mars Express orbiter has already began its observation campaign and will be taking photos and analyzing the composition of the comet’s coma over the next two weeks. The comet will be at its closest to Mars on October 1, at a distance 6 times closer than it will approach Earth.
The NASA/ESA joint-project Solar And Heliospheric Observatory (SOHO) mission, ground based at Goddard Space Flight Center, will view the comet as it swings around the Sun in late November, with astronomers waiting to see if the comet survives this fiery encounter.
NASA has initiated a Comet ISON Observing Campaign to facilitate a global observation campaign incorporating both space-based and ground-based telescopes and encouraging citizen scientists as well as both professional and amateur astronomers to participate.