A Comet Active Beyond the Crystallization Zone

  title={A Comet Active Beyond the Crystallization Zone},
  author={D. Jewitt and M. Hui and M. Mutchler and H. Weaver and J. Li and J. Agarwal},
  journal={arXiv: Earth and Planetary Astrophysics},
We present observations showing in-bound long-period comet C/2017 K2 (PANSTARRS) to be active at record heliocentric distance. Nucleus temperatures are too low (60 K to 70 K) either for water ice to sublimate or for amorphous ice to crystallize, requiring another source for the observed activity. Using the Hubble Space Telescope we find a sharply-bounded, circularly symmetric dust coma 10$^5$ km in radius, with a total scattering cross section of $\sim$10$^5$ km$^2$. The coma has a logarithmic… Expand

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