Abstract

The photometric properties of the nucleus of comet 9P/Tempel 1 are studied from the disk-resolved color images obtained by Deep Impact (DI). Tempel 1 has typical photometric properties for comets and dark asteroids. The phase function of Tempel 1 is constructed from DI images and earlier ground-based observations found from the literature. The phase coefficient is determined to be b=0.046±0.007 mag/deg (you should briefly note the range of phase angles for which this is valid). The Hapke asymmetry factor is estimated to be g=-0.49±0.02. The disk-integrated spectrum of the nucleus of Tempel 1 between 309 nm and 950 nm areis linear without any features at the spectral resolution of these filtered images. The red slope of the nucleus is 12.5±1% per mm, translating to B-V=0.83±0.01, V-R=0.50±0.01, and R-I=0.52±0.01. No phase reddening is observed. The single-scattering albedo (SSA) of Tempel 1 is modeled to be 0.039±0.005 at 550 nm, very close to other comets and dark asteroids. The SSA spectrum shows a similar linear slope to that of the disk-integrated spectrum. The roughness parameter is found to be 16°±8°, similar to other comets and asteroids, and independent of wavelength. The Minnaert k parameter is modeled to be 0.680±0.014. The photometric variations (FWHM?)on Tempel 1 are relatively small compared to other comets and asteroids, with ~12% albedo variations, and ~3% for color. Roughness variations are evident in one small area around the lower-right limb, with a roughness parameter about twice the average, and correlates with the complex morphological texture seen in high-resolution images.