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Session 116 - The Solar System.
Oral session, Thursday, January 18
Salon del Rey Central, Hilton

[116.06] Disk-Resolved Images of Pluto and Ceres from the Hubble Space Telescope

S. A. Stern, B. C. Flynn (SwRI), M. W. Buie (Lowell Obs.), R. P. Binzel (MIT), M. C. Festou (Obs. Midi-Pyrènees), L. A. Lebofsky (UA/LPL), L. M. Trafton (UT/McDonald Obs.)

We have obtained high-resolution images of Pluto and 1 Ceres using the Hubble Space Telescope (HST) Faint Object Camera (FOC). These images provide the first direct albedo maps of these two interesting objects.

We obtained the Pluto images on four dates in June and July 1994. These images were made in two color bandpasses, one centered near 410 nm and the other centered near 278 nm. These bandpasses were chosen to discriminate between icy and refractory surface materials. Together, the four sets of images provide nearly-complete longitudinal coverage of Pluto, with a typical S/N 20 per resolution element in the 410 nm images. The resolution and S/N are sufficient to show a complex suite of large scale spots and large, longitudinally-asymmetric polar cap regions. The 278nm images show many of the same features, but at S/N 10. In addition to being used for mapping purposes, the HST/FOC dataset is being analyzed to (i) obtain information on Charon's lightcurve, (ii) constrain any north/south albedo asymmetry on Charon, (iii) better determine Pluto's limb darkening coefficient, and (iv) search for evidence of small satellites in the inner Pluto-Charon system.

In June 1995, we obtained two sets of HST/FOC Ceres images in three color bandpasses, centered near 342 nm, 278 nm, and 150 nm. The 150 nm images do not contain enough S/N to be interpreted as maps, however, the 342nm blue and 278nm UV images show distinct albedo units hundreds of km across on the surface of the asteroid. As a part of the mapping effort we have undertaken with these images, we note that these images are useful for constraining the presence of possible H_2O caps on Ceres.

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