The solar system contains solids of all sizes, ranging from km-size bodies to nano-sized particles. Nanograins have been detected in situ in the Earths atmosphere, near cometary and giant planet environments, and more recently in the solar wind at 1
AU. These latter nano grains are thought to be formed in the inner solar system dust cloud, mainly through collisional break-up of larger grains and are then picked-up and accelerated by the magnetized solar wind because of their large charge-to-mass ratio. In the present paper, we analyze the low frequency bursty noise identified in the Cassini radio and plasma wave data during the spacecraft cruise phase inside Jupiters orbit. The magnitude, spectral shape and waveform of this broadband noise is consistent with the signature of nano particles impinging at nearby the solar wind speed on the spacecraft surface. Nanoparticles were observed whenever the radio instrument was turned on and able to detect them, at different heliocentric distances between Earth and Jupiter, suggesting their ubiquitous presence in the heliosphere. We analyzed the radial dependence of the nano dust flux with heliospheric distance and found that it is consistent with the dynamics of nano dust originating from the inner heliosphere and picked-up by the solar wind. The contribution of the nano dust produced in asteroid belt appears to be negligible compared to the trapping region in the inner heliosphere. In contrast, further out, nano dust are mainly produced by the volcanism of active moons such as Io and Enceladus.
Nanodust grains of a few nanometer in size are produced near the Sun by collisional break-up of larger grains and picked-up by the magnetized solar wind. They have so far been detected at 1 AU by only the two STEREO spacecraft. Here we analyze the sp
ectra measured by the radio and plasma wave instrument onboard Cassini during the cruise phase close to Earth orbit; they exhibit bursty signatures similar to those observed by the same instrument in association to nanodust stream impacts on Cassini near Jupiter. The observed wave level and spectral shape reveal impacts of nanoparticles at about 300 km/s, with an average flux compatible with that observed by the radio and plasma wave instrument onboard STEREO and with the interplanetary flux models.
