Nanodust detection between 1 and 5 AU by using Cassini wave measurements

TL;DR

This study detects and analyzes nanodust particles in the heliosphere using Cassini wave data, revealing their widespread presence and radial flux dependence, mainly originating from the inner solar system and moon volcanism.

Contribution

It provides the first in situ detection of nanodust between 1 and 5 AU using Cassini data and characterizes their flux and origin in the heliosphere.

Findings

Nanodust detected at various distances from Earth to Jupiter.

Radial flux decreases with heliocentric distance, consistent with inner heliosphere origin.

Inner solar system and moon volcanism are primary sources of nanodust.

Abstract

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.