Cassini between Venus and Earth: detection of interstellar dust grains

Details Cassini between Venus and Earth: detection of interstellar dust grains Cassini between Venus and Earth: detection of interstellar dust grains

Apr 2003

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003eaeja.....8767a&link_type=abstract

EGS - AGU - EUG Joint Assembly, Abstracts from the meeting held in Nice, France, 6 - 11 April 2003, abstract #8767

Computer Science

Scientific paper

Dust measurements by the instruments on the Ulysses and Galileo spacecraft outside 3 AU heliocentric distance revealed a collimated source of interstellar particles. The directionality of the observed flux was compatible with the flow direction of the gas of the Local Interstellar Cloud (LIC) of 252 deg ecliptic longitude and 5.2 deg ecliptic latitude. Both, the dust size distribution and the mean dust mass of 10^(-16)kg indicated the existence of bigger grains than those derived from optical observations of the LIC. Here we report about the successful in-situ measurement of interstellar dust particles within the inner solar system by the Cosmic Dust Analyser (CDA) on the Cassini spacecraft in 1999 between Venus and Earth. The impact ionisation subsystem of the CDA is similar to the Ulysses-typeinstruments. Dust particles striking the impact target generate a mixture of impact plasma and ejecta. The plasma constituents are collected by charge amplifiers and converted into an electrical signal. The collected charge is a function of the dust mass and the impact velocity, while the charge signal rise time depends upon the velocity only. Although the transmitted charge signals of big particle impacts differ significantly from laboratory results, we succeeded reliably in distinguishing between interstellar impactors and grains of interplanetary origin by their impact ion charge. As the heliocentric velocity and the direction of the interstellar dust flux are well known, a joint analysis of the impact charge signals together with geometric and kinematic spacecraft data at impact time allowed us to separate interplanetary impacts from interstellar ones. The interstellar flux measured by Cassini at 0.8 AU is in good agreement with the flux measured by Ulysses at 3 AU at the same time. The simultaneous detection of interstellar grains at 3 AU and 0.8 AU prove that big interstellar grains are able to penetrate deeply into the inner solar system.

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