The Scientific Importance of Comet C/2012 S1 (ISON) Spitzer 6/13/13 Mercury Dust Gas Sol Mars HST 4/10/13 Jet? Ice Dust Earth The Scientific Importance of Comet C/2012 S1 (ISON) First passage of comet through inner solar system since formation and ejection - Likely contains some of the most pristine material left in the solar system - Detailed orbital knowledge for an Oort comet perturbed many Mya to into inner system On a Sungrazing Orbit, with > 1 yr lead time since discovery - Perihelion on Nov 28, 2013 at rh = 2.7 RSun, so close all dust & gas will atomize ISON will have close encounters with Mars (C.A. = 0.07 AU), Mercury (C.A. = 0.24 AU), Sol, Earth(?) (C.A. = 0.44AU), & Venus (C.A.=0.42 AU) in 2013. The last time(s) this happened, in 1965 with Comet Ikeya-Seki, we observed one of the 10 brightest comets ever as it disintegrated at the Sun; and in 1973, when Comet Kohoutek mysteriously bloomed in the outer S.S. then faded away. But now we have > 18 s/c at Mars, Venus, Mercury, Earth, and others watching the Sun 24/7, that can study ISON. Earth