Spectroscopy of Pluto's Small Satellites
Abstract
On July 14, 2015, New Horizons made its closest approach to the Pluto system. Among its many tasks were spectroscopic observations of Nix, Hydra and Kerberos using LEISA (Linear Etalon Imaging Spectral Array), the near infrared imaging spectrograph, and component of the Ralph instrument (Reuter, D.C., Stern, S.A., Scherrer, J., et al. 2008, Space Sci. Rev. 140, 129). Shapes and composition inferred from images were discussed in Weaver et al. (2016, Science, 351). Styx was not observed with LEISA because it was too distant and faint.Observations of Nix were made at 60,000 and 162,000 km from New Horizons. At best, Nix filled ∼130 LEISA pixels. At the continuum level, the disk integrated spectrum has an I/F∼0.4 and a blue slope. Evident in the spectrum are deep bands at 1.5, 1.65 and 2.0 μm, indicating crystalline H2O-ice. At band minimum, the I/F∼0.1 and 0.05 for the 1.5 and 2.0 μm bands, respectively. These nearly saturated bands suggest that H2O-ice is either large grained or very pure. We also see an absorption band at 2.21 μm that well matches NH3-hydrate.Observations of Hydra were made at 240,000 and 370,000 km from New Horizons. Hydra was barely resolved and covered ∼3-5 LEISA pixels. Hydra's spectrum has a continuum I/F∼0.35, a blue slope weaker than Nix's, crystalline H2O-ice and the 1.5 and 2.0 μm bands have minimum I/F∼0.12 and 0.07, respectively. Since the bands on Hydra are slightly weaker, the H2O-ice grains are either smaller or contaminated by a greater fraction of dark material. Hydra's spectrum also shows the NH3-hydrate absorption at 2.21 μm, but like the H2O-ice bands, it too appears weaker on Hydra than Nix.Finally, New Horizons made a LEISA observation of Kerberos at 394,000 km distance. At a scale of 24 km/pix, Kerberos fills ∼40% of a LEISA pixel. The signal-to-noise of the data is low. Nonetheless, we attempt to extract the spectrum.At DPS, we will present spectra of all three objects, examine the disk resolved spectra of Nix, present Hapke models and discuss why the H2O and NH3-hydrate bands appear deeper on Nix and Hydra than on Charon.This work was supported by NASA's New Horizons project.
- Publication:
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AAS/Division for Planetary Sciences Meeting Abstracts #48
- Pub Date:
- October 2016
- Bibcode:
- 2016DPS....4820503C