  The Rosetta lander Philae successfully landed on the nucleus of comet
67P/Churyumov-Gerasimenko on 12 November 2014. Philae carries the Dust Impact
Monitor (DIM) on board, which is part of the Surface Electric Sounding and
Acoustic Monitoring Experiment (SESAME). DIM employs piezoelectric PZT sensors
to detect impacts by sub-millimeter and millimeter-sized ice and dust particles
that are emitted from the nucleus and transported into the cometary coma. The
DIM sensor measures dynamical data like flux and the directionality of the
impacting particles. Mass and speed of the particles can be constrained
assuming density and elastic particle properties. DIM was operated during three
mission phases of Philae at the comet: (1) Before Philae's separation from
Rosetta at distances of about 9.6 km, 11.8 km, and 25.3 km from the nucleus
barycenter. In this mission phase particles released from the nucleus on radial
trajectories remained undetectable because of significant obscuration by the
structures of Rosetta, and no dust particles were indeed detected. (2) During
Philae's descent to its nominal landing site Agilkia, DIM detected one
approximately millimeter-sized particle at a distance of 5.0 km from the
nucleus' barycenter, corresponding to an altitude of 2.4 km from the surface.
This is the closest ever dust detection at a cometary nucleus by a dedicated
in-situ dust detector. (3) At Philae's final landing site, Abydos, DIM detected
no dust impact which may be due to low cometary activity in the vicinity of
Philae, or due to shading by obstacles close to Philae, or both. Laboratory
calibration experiments showed that the material properties of the detected
particle are compatible with a porous particle having a bulk density of
approximately $250\, \mathrm{kg\,m^{-3}}$. The particle could have been lifted
off from the comet's surface by sublimating water ice.
