PP - Permittivity Probe

Measuring principle of PP with transmitting (TX) and receiving

The Permittivity Probe shall determine the water ice content in the cometary surface layer and its variation with time.

To this end PP employs the quadrupole technique, where two electrodes, connected with an AC generator, induce a variable current into the cometary matter. Two additional electrodes detect the resulting voltage and phase. There are three transmitter electrodes on the Philae cometary lander (one in a lander foot and the other two close to the sensors of the experiments MUPUS-Pen and APXS).The two receiving electrodes are mounted into the soles of the remaining two feet (see CASSE page). Using the variable geometry of different transmitter electrode combinations one can infer the complex permittivity down to a depth of about 2 m.

Thus one can determine the electrical conductivity and the relative permittivity. These material parameters react quite sensitive to the amount of polar molecules, especially water, and their temperature. Using these data one can calculate the water content of the surface, which can vary during one comet day and with the distance of the comet to the Sun, and possibly also the water vapor production rate. From this it is possible to describe the outgassing behavior and to infer the composition of the comet.

PP electrode (brown mesh) below the hammering mechanism of the MUPUS-Pen experiment

Operating in passive mode, the PP instrument can detect plasma waves up to 10 kHz, which originate from the interaction of the Solar Wind with the emitted cometary particles and gas and are a measure of the cometary activity. PP was developed and built at the Finnish Meteorological Institute (FMI), Helsinki, in collaboration with the ESA technology center ESTEC.

Properties of PP
Sounding frequency	0.01 to 10 kHz
Receiving frequency	20 kHz
Mass	270 g
Power	≤ 320 mW

Link:

• Permittivity Probe (FMI-Finnish Meteorological Institute)