The STEREO mission, that has now been in scientific activity for more than 5 years, is made of two identical spacecraft orbiting the Sun at around one astronomical unit. The primary goal of the mission if the study of the coronal activity and mass ejections.
The S/WAVES radio instrument onboard these spacecraft is designed to study the electromagnetic field in frequencies ranging from ~1 kHz to ~10 MHz. It is made of three 6m electric antennas connected to an electronic analyzer. The study of the data provided by S/WAVES showed the very frequent occurrence of electric pulses of local origin.
Following series of previous work (started in the 80′s with Voyager’s radio experiment) these impulsive signals were interpreted as being a signature of the high-velocity impact of dust particles on the spacecraft surface. A mass calibration allowed us to determine the size of the grains impacting the spacecraft to be of the order of 10 nm. The dust flux derived from S/WAVES observations was found to be consistent with the interpolation of classical models to small masses.
The STEREO measurements are thus likely the first in-situ measurement of nano-meter dust grains in the vicinity of Earth orbit.
The more detailed study of the individual impacts using the S/WAVES TDS waveform sampler showed that another kind of impulsive signals, much less frequent, could be observed in the data. We interpret them as being due to grains in the micro-meter range, and obtain a flux curve modulated with longitude along the interstellar drift direction of the solar system. This modulation enables us to perform a measurement of the interstellar dust flux in the size range 0.1-0.3 microns at 1 AU.
I will present the works undertaken at the Observatory of Paris on the dust detection by the S/WAVES radio instrument : the theoretical modelization of the observed signals, the mass calibration linking the signals amplitude to the mass/size of the impinging grains, and the results of the STEREO data analysis on the 2007-2011 period, in the nano and the micron size ranges.