First dust measurements with the Solar Orbiter Radio and Plasma Wave instrument

Abstract

Impacts of dust grains on spacecraft are known to produce typical impulsive signals in the voltage waveform recorded at the terminals of electric antennas. Such signals are routinely detected by the Time Domain Sampler (TDS) system of the Radio and Plasma Waves (RPW) instrument aboard Solar Orbiter. We investigate the capabilities of RPW in terms of interplanetary dust studies and present the first analysis of dust impacts recorded by this instrument. We discuss previously developed models of voltage pulses generation after a dust impact onto a spacecraft and present the relevant technical parameters for Solar Orbiter RPW as a dust detector. Then we present the statistical analysis of the dust impacts recorded by RPW/TDS from April 20th, 2020 to February 27th, 2021 between 0.5 AU and 1 AU. The study shows that the dust population studied presents a radial velocity component directed outward from the Sun, the order of magnitude of which can be roughly estimated as $v_{r,dust}\simeq 50$ km.$s^{-1}$. This is consistent with the flux of impactors being dominated by $\beta$-meteoroids. We estimate the cumulative flux of these grains at 1 AU to be roughly $F_{\beta }\simeq 8\times 10^{-5}$ m${}^{-2}$s${}^{-1}$, for particles of radius $r\gtrsim 100$ nm. The power law index $\delta$ of the cumulative mass flux of the impactors is evaluated by two differents methods (direct observations of voltage pulses and indirect effect on the impact rate dependency on the impact speed). Both methods give a result $\delta \simeq 0.3-0.4$. Solar Orbiter RPW proves to be a suitable instrument for interplanetary dust studies. These first results are promising for the continuation of the mission, in particular for the in-situ study of the dust cloud outside the ecliptic plane, which Solar Orbiter will be the first spacecraft to explore.

13 pages, 8 figures

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• The Solar Orbiter mission -- Science overview
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• The Near-Sun Dust Environment: Initial Observations from Parker Solar Probe
• The importance of monopole antennas for dust observations: why Wind/WAVES does not detect nanodust
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• Modelling Solar Orbiter Dust Detection Rates in Inner Heliosphere as a Poisson Process
• Alpha-Meteoroids then and now: Unearthing an overlooked micrometeoroid population
• Size distribution of small grains in the inner zodiacal cloud
• A solar rotation signature in cosmic dust: frequency analysis of dust particle impacts on the Wind spacecraft
• On the distribution of the the near-solar bound dust grains detected with Parker Solar Probe
• Astrophysically sourced quantum coherent photonic signals