  Micrometeoroids (cosmic dust with size between a few $\mu$m and $\sim$1 mm)
dominate the annual extraterrestrial mass flux to the Earth. We investigate the
range of physical processes occurring when micrometeoroids traverse the
atmosphere. We compute the time (and altitude) dependent mass loss, energy
balance, and dynamics to identify which processes determine their survival for
a range of entry conditions. We develop a general numerical model for the
micrometeoroid-atmosphere interaction. The equations of motion, energy, and
mass balance are simultaneously solved for different entry conditions (e.g.
initial radii, incident speeds and angles). Several different physical
processes are taken into account in the equation of energy and in the mass
balance, in order to understand their relative roles and evolution during the
micrometeoroid-atmosphere interaction. In particular, to analyze the
micrometeoroid thermal history we include in the energy balance: collisions
with atmospheric particles, micrometeoroid radiation emission, evaporation,
melting, sputtering and kinetic energy of the ablated mass. Low entry
velocities and grazing incidence angles favor micrometeoroid survival. Among
those that survive, our model distinguishes (1) micrometeoroids who reach the
melting temperature and for which melting is the most effective mass loss
mechanism, and (2) micrometeoroids for which ablation due to evaporation causes
most of the the mass loss. Melting is the most effective cooling mechanism.
Sputtering-induced mass loss is negligible.
