Catalogued as C/2012 S1, Comet ISON was first spotted 585 million miles away in September 2012. This is ISON's very first trip into the inner solar system. That means it is still made of pristine matter from the earliest days of the solar system’s formation, its top layers never having been lost by a trip near the sun. Along Comet ISON's journey, NASA has used a vast fleet of spacecraft and Earth-based telescopes to learn more about this time capsule from when the solar system first formed.
During the last week of its inbound trip, ISON will enter the fields of view of NASA’s space-based solar observatories. Comet ISON will be viewed first by NASA's Solar Terrestrial Relations Observatory, or STEREO. Next the comet will be seen in what’s called coronagraphs by both STEREO and the joint European Space Agency/NASA Solar and Heliospheric Observatory, or SOHO. Then, NASA’s Solar Dynamics Observatory will view the comet for a few hours during its closest approach to the sun, known as perihelion.