[Previous] | [Session 49] | [Next]
M. W. Buie, W. M. Grundy (Lowell Observatory)
Pluto is approaching an epoch of rapidly changing geometry where its heliocentric distance is increasing and the sub-solar latitude is moving away from the equator. These changes may or may not lead to observable changes on the surface but they will lead to apparent changes just due to the evolving geometry.
We observed Pluto during the 1996-1998 apparitions with broad-band visual photometry and with low-resolution infrared spectroscopy. The photometry is all in Johnson B and V filters plus one filter centered on the 8900Å-band CH4 absorption band. These data monitor for changes in disk-integrated brightness and changes in color. The spectroscopic data cover the 1--2.3\mum spectral region which include features from CH4, N2, CO, and H2O frosts. The spectra are sensitive to certain conditions of temperature and crystalline state on the surface. Both types of data are sampled over the complete range of rotational aspect and solar phase angle. So far, we have collected over 70 nights of photometric data and 100 nights of spectroscopic data.
We will present results of our monitoring program with a particular emphasis on the disk-integrated brightness evolution and the degree of spectral variation seen with rotation, solar phase angle, and time. This work was supported by NASA Grants, NAGW-5009, NAG5-4210, and STScI Grant HF-01091.01-97A.