A two-spot albedo model for the surface of Pluto

by: Marcialis, R. L.

ABSTRACT

This paper summarizes the work of Marcialis (1983, 1984). A finite-element
approach has been used to generate synthetic light curves of an unevenly
bright, rotating sphere. Application to the Pluto-Charon system shows that
two circular spots (46 and 28 deg in radius, both at south latitude 23
deg, separated by 134 deg in longitude) with albedos half that of the
surrounding terrain can accurately reproduce six available photoelectric
light curves between 1953 and 1982. A dark equatorial band (extending from
south latitude 69 deg to anywhere between 50 and 65 deg north latitude)
can be invoked to explain the secular dimming. Constraints on this equator-
ial band, which may alternatively be viewed as two polar caps, are such
that to date its dimensions are not uniquely determined. However, polar
caps with albedos near unity serve quite well to explain the 40-percent
dimming of Pluto since its discovery in 1930. Hardie's 1964 photoelectric
observations are presented for the first time in tabular form.

Astronomical Journal, ISSN 0004-6256, vol. 95, March 1988, p. 941-947.