Pluto’s global surface composition through pixel-by-pixel Hapke modeling of New Horizons Ralph/LEISA data
Icarus Elsevier 287 (2017) 218-228
The near-surface electron radiation environment of Saturn's moon Mimas
Icarus Elsevier 286 (2017) 56-68
Thermally anomalous features in the subsurface of Enceladus’s south polar terrain
Nature Astronomy Springer Nature 1:4 (2017) 0063
The formation of Charon's red poles from seasonally cold-trapped volatiles.
Nature 539:7627 (2016) 65-68
Abstract:
A unique feature of Pluto's large satellite Charon is its dark red northern polar cap. Similar colours on Pluto's surface have been attributed to tholin-like organic macromolecules produced by energetic radiation processing of hydrocarbons. The polar location on Charon implicates the temperature extremes that result from Charon's high obliquity and long seasons in the production of this material. The escape of Pluto's atmosphere provides a potential feedstock for a complex chemistry. Gas from Pluto that is transiently cold-trapped and processed at Charon's winter pole was proposed as an explanation for the dark coloration on the basis of an image of Charon's northern hemisphere, but not modelled quantitatively. Here we report images of the southern hemisphere illuminated by Pluto-shine and also images taken during the approach phase that show the northern polar cap over a range of longitudes. We model the surface thermal environment on Charon and the supply and temporary cold-trapping of material escaping from Pluto, as well as the photolytic processing of this material into more complex and less volatile molecules while cold-trapped. The model results are consistent with the proposed mechanism for producing the observed colour pattern on Charon.Charon's light curves, as observed by New Horizons’ Ralph color camera (MVIC) on approach to the Pluto system
Icarus Elsevier 287 (2016) 152-160