Published online by Cambridge University Press: 27 February 2018
Three topics are briefly reviewed to examine evidence for the nature of dust grains and grain alteration by physical processes related to mainly sublimation. Namely, (1) a change of dust flux detected by in situ dust measurements beyond ~ 2 AU from the Sun suggests a disappearance of volatile ices due to sublimation below this distance, (2) an elongation angle dependence of Doppler shifts observed in the zodiacal light can be explained by the introduction of a dependence of the orbital velocity on the radiation pressure forces acting on the grains, taking into account a variation of dust structure with heliocentric distance, and (3) the variation of color temperature observed in cometary coma suggests a loss of carbon content from cometary dust grains due to sublimation. This piece of evidence agrees with the generation of carbon-bearing molecules from extended sources, as infered from observations in cometary comae.