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W.M. Grundy, M.W. Buie (Lowell Observatory)
Since 1994, we have been engaged in a campaign of H- and K-band spectral monitoring of Pluto/Charon, using spectrometers at Anderson Mesa, Kitt Peak, and Mauna Kea, with spectral resolutions \geq300. In this wavelength region, Pluto's spectrum shows absorptions bands of CH4, H2O, and N2 ices. Spectral contamination by Pluto's satellite Charon is removed using procedures described by Buie and Grundy [2000].
Our objective is to monitor changes in Pluto's spectrum as Pluto's sub-solar and sub-earth latitudes move north, bringing the north polar cap into view. Until recently, this region was in permanent darkness and atmospheric species such as N2, CO, and CH4 likely condensed as ices there. Additionally, Pluto's surface has been predicted to undergo textural and compositional evolution, driven by solar heating [Grundy and Stansberry 2000]\null. This processing would proceed most rapidly around the time of Pluto's perihelion passage, influencing the distribution of minority species CO and CH4 within Pluto's N2 ice. Finally, photometric data suggest the possibility of episodic events affecting the surface of Triton [e.g.\ Buratti et al.\ 1999]\null. No such events have been reported for Pluto, but processes active on Triton could affect Pluto's surface as well.
We have data from well over 100 nights. Such intensive sampling is required, if we are to distinguish diurnal, transient, and seasonal spectral effects. We will report results from our on-going campaign, with emphasis on behavior of Pluto's CH4 and N2 ice absorption bands.
This work has been supported by Hubble Fellowship grant HF-01091.01-97A, by NASA grant NAG5-4201, and by NSF's REU program.
Buie, M.W. and W.M. Grundy 2000. The distribution and physical state of H2O on Charon. Icarus (in press).
Buratti, B.J., M.D. Hicks, and R.L. Newburn~Jr.\ 1999. Does global warming make Triton blush? Nature 397, 219.
Grundy, W.M. and J.A. Stansberry 2000. Solar gardening and the seasonal evolution of nitrogen ice on Triton and Pluto. Icarus (in press).