Seasonal Volatile Transport and Plumes on Pluto

English Abstract:

The New Horizons spacecraft will reach Pluto for a close flyby in July 2015. To place this singular event within the context of temporal changes on Pluto, ground-based monitoring programs have been gathering observations on this dwarf ice planet for decades. Several lines of evidence support volatile transport on its surface: changes in the rotational light curve of Pluto beyond those expected from viewing geometry alone; changes in albedo patterns mapped by ground-based Hubble Space Telescope Maps (Buie et al., 2010, A. J. 139, 1117); and changes in atmospheric pressure(Young et al. 2013, Ap. J. Lett. 766, L22). Both Mars and Triton, the Neptunian moon that is Pluto’s twin, exhibit seasonal volatile frost transport, and both have plumes or plume deposits on their polar caps that are believed to result from the sublimation of the cap. A dark substrate (dust in the case of Mars, and photolyzed methane in the case of Pluto) below nitrogen ice (Triton or Pluto) or carbon dioxide ice (Mars) heats up under solar insolation to create a solid state greenhouse effect. Subsurface volatiles sublimate and catastrophically outgas to form dark plumes. The similarities between Triton and Pluto, including surface temperature, size, obliquity, distance from the sun, and composition, coupled with the good evidence for currently active seasonal volatile transport of Pluto, lead us to predict this dwarf planet will have plumes similar to those on Triton. Given the lack of tidal heating on Pluto, these plumes will be the prime active process on Pluto’s surface. During our campaign monitoring the lightcurve of Pluto, we discovered a remarkable opposition effect with the 24-inch telescope at Table Mountain Observatory. As this surge is not visible with the New Horizons spacecraft (it never achieves sufficiently small solar phase angles), its discovery illustrates another example in which ground-based observations are complementary to those of spacecraft.

Funded by NASA