ИСТИНА

As follows from ground-based spectrophotometric observations of (1) Ceres performed by several research groups, the visible-range slope of its reflectance spectra varied during a period of 1975 to 2013. The only regular factor, the effect of which on the reflectance spectra of Ceres we found, is solar activity events (X-ray flares and accompanied coronal mass ejections). Such events induce the emergence of a tenuous exosphere on, which changes the reflectance spectra of Ceres’ surface. The light-scattering modeling showed that reflectance spectra of an asteroid may exhibit a distinct negative gradient if its exosphere is composed of H2O-ice aggregates of submicron constituents. A positive gradient is typical of reflectance spectra of an asteroid with an exosphere consisting of Fe-Mg aggregates of submicron particles.