IMAGES OF PLUTO GENERATED BY MATRIX LIGHTCURVE INVERSION

We use a new indirect imaging method, matrix lightcurve inversion (MLI ), to generate surface albedo maps of Pluto from the rotational photom etric Lightcurves. The mathematical basis of MLI is established and a constrained iterative regularization method used to invert the underde termined system of equations. Lf the secular dimming of Pluto observed in all phases of the rotational lightcurves from 1954 to 1982, follow ed by an overall brightening of the planet in later years, could be as cribed to a static surface albedo distribution, then an albedo map can be generated using all the available lightcurves. However, Stern et a l. (1988, Icarus 75, 485-498) have suggested that an extensive coverin g of methane frost sublimates as Pluto approaches perihelion, exposing dark layers of photolyzed methane in a spatially nonuniform pattern, and then freezes out again as Pluto passes perihelion. Assuming that S tern et al. (1988, Icarus 75, 485-498) are correct in their interpreta tion that Pluto undergoes atmospheric sublimation and freezeout cycles , we present an image that represents a snapshot of Pluto as it might have appeared during the interval 1980 to 1986 by using lightcurves me asured in these years. Another image using the lightcurves between 195 4 and 1986 shows very extensive and bright polar caps though this imag e appears to be highly unrealistic. We propose that the inability to f it these lightcurves (to even remotely within the noise level in the d ata) furnishes evidence to the hypothesis of large-scale and dynamic a tmospheric volatile transport over Pluto's surface between the mid 195 0s and the mid 1980s. (C) 1995 Academic Press, Inc.