  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 Earth's
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 Jupiter's 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.
