THE OPTICAL-SPECTRUM OF 5145 PHOLUS

The optical reflectance spectrum of the outer Solar System object 5145 Pholus (preliminary designation, 1992 AD) was measured with 10 Å per pixel dispersion over the wavelength range 4400-9600 Å using the Hiltner 2.4-m telescope of the Michigan Dartmouth MIT Observatory and a CCD spectrograph. No emission lines were detected. A linear slope of 0.47 ± 0.03/103 A ̊ was measured for wavelengths beyond 5500 Å, a reflectance slope value intermediate between two slopes reported previously. The steep red slope suggests the presence of organic material on the object's surface, leading to the hypothesis that the object has a primitive composition and is at either the beginning or the end state of its thermal evolution. © 1992.