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Brightness and Orbital Motion Peculiarities of Comet C/2012 S1 (ISON): Comparison with Two Very Different Comets

To gain a greater insight into the impending evolution of the physical behavior of comet C/2012 S1, its light curve and orbital properties are compared with those for C/1962 C1 (Seki-Lines) and C/2002 O4 (Hoenig). All three are likely Oort Cloud comets. C/1962 C1 survived an encounter with the Sun at less than 7 Rsun, while C/2002 O4 disintegrated near perihelion at 0.78 AU from the Sun. Less than two months before its perihelion at 2.7 Rsun, C/2012 S1 has a light curve that is much closer to C/1962 C1 than C/2002 O4. It remains to be seen whether its motion is affected by nongravitational perturbations. As new data on C/2012 S1 keep coming in, its continuing comparison with the two comets will provide information on its health by updating and adjusting its status. Strengths and weaknesses of this approach for potential future applications will eventually be assessed.