Dynamics of dust grains with a vaporable icy mantle

We show the effects of solar gravity, electromagnetic radiation and solar wind on the motion of micrometre-sized interplanetary dust grains for initially small eccentric orbits and for heliocentric distances less than 10 au. The traditional approach is that the solar wind effect and the Poynting-Robertson (P-R) effect are simultaneously taken into account through the numerical factor 1 + eta A/(C) over bar (pr), which is multiplied by the P-R effect. In reality, solar wind corpusculae erode the surface of the interplanetary grain. As a consequence, the value of the solar electromagnetic radiation pressure term increases, as it is inversely proportional to the size of the grain. In addition, the radiation pressure efficiency also varies because of the changes to the optical properties of the grain. Both these physical processes are taken into account, and the secular evolution of orbital elements for a Gaussian sphere with a volatile icy coating exhibits a secular increase of the semimajor axis and eccentricity as well as the longitude of perihelion. These secular changes of orbital elements do not exist in the conventional approach for the P-R and solar wind effects. The conventional approach yields 10(4) yr for the lifetime of inspiralling toward the Sun, if the evolution starts from the initial values of the semimajor axis a(in) = 4 au and eccentricity e(in) = 0.2. The Gaussian sphere with a volatile icy coating exhibits a semimajor axis greater than 10 au for t > 3 x 10(2) yr for the same initial orbital elements.