Comet ISON (C/2012 S1) is a recently discovered sungrazing comet that will reach perihelion in November 2013 less than 2 solar radii from the Sun’s photosphere. While it is still more than 3.5 AU from the Sun and is currently relatively faint, it is predicted to become very bright near perihelion and has therefore gained considerable notoriety. A worldwide observing campaign to characterize ISON is underway and will include observations from the ground, space-based telescopes, solar observatories, and a number of NASA assets throughout the inner solar system.
The early discovery and high community interest in ISON have allowed greater study of it prior to the onset of water-driven activity than is typical for long period comets. I will discuss the current state of knowledge of Comet ISON, including recent HST imaging and spectroscopy programs in which I have been involved. I will review past observations of sungrazing comets as a means for understanding how Comet ISON is likely to behave near perihelion. Of particular note are considerations of whether or not it will survive both erosion and disruption, and how it might be used as a “solar probe” when viewed by space-based solar observatories such as SOHO, STEREO, and SDO. Finally, I will discuss the epochs at which ISON will be observable by different methods (including naked eye and with MAVEN) and what new science may be revealed during this unprecedented apparition.