The sublimation of the volatile constituents of the cometary surface - mainly water ice – carries away dust and ice particles with sizes ranging from micrometer to centimeter. If their initial velocity is too small to leave the cometary gravitational field, they fall back to the cometary surface.
The DIM sensor cube, which is mounted at the upper edge of the balcony of Philae, registers impacting particles from three directions with piezo plates and the electronics analyses the signals with respect to their wave-form (amplitude and contact duration). From this data and plausible assumptions of the particle density one can deduce the masses of the particles, their velocities, number, directional distribution and the time dependence of these parameters. From these data one can deduce the starting velocities of the particles that are correlated with the outgassing velocity and the flux of the cometary gases.
DIM was developed and built at the Atomic Energy Research Institute (EK) of the Hungarian Academy of Sciences (MTA) in Budapest. Now the Max-Planck-Institute of Solar System Research (Katlenburg, Germany) takes care of the DIM instrument.