Cassini between Earth and asteroid belt: first in-situ charge measurements of interplanetary grains

Details Cassini between Earth and asteroid belt: first in-situ charge measurements of interplanetary grains Cassini between Earth and asteroid belt: first in-situ charge measurements of interplanetary grains

Oct 2004

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004icar..171..317k&link_type=abstract

Icarus, Volume 171, Issue 2, p. 317-335.

Astronomy and Astrophysics

Astrophysics

20

Interplanetary Dust, Solar Wind, Celestial Mechanics, Data Reduction Techniques

Scientific paper

Dust particles in interplanetary space are expected to charge up to an electrostatic potential of about +5 V mostly by the solar UV (Horányi, 1996, Annu. Rev. Astrophys. 34, 383). Since the dynamics of charged grains may be quite different from neutral particles, the knowledge of the grain charge Qd is highly desirable. In the last two decades, several detectors on spacecraft were flown to measure the dust charge in-situ, but the instrumentation was not capable of determining the dust charge unambiguously. The Cosmic Dust Analyser (CDA) on the Cassini spacecraft includes a charge sensitive entrance grid system (QP detector). While entering the instrument, sufficiently charged particles induce a characteristic charge feature onto the grid system, which allows a reliable determination of Qd as well as of the impact speed vd. Here we report the first successful in-situ measurement of charged interplanetary dust grains by CDA. Amongst 37 impacts by interplanetary grains registered between November 1999 and January 2000, we identified 6 impacts whose QP signals show a clear feature caused by charged grains, corresponding to Qd between 1.3 and 5.4 fC. Knowledge of Qd also allows us to estimate the grain mass md. Assuming a potential of φd~+5 V and spheroidal grain morphologies with ratios of the maximum size to the minimum size of less than 2 the masses derived from Qd were found to be in excess of 10-13 kg. The dynamics of such particles are dominated by the Sun's gravity. In the framework of the micro-meteoroid models of the Solar System these grains belong to the core population of interplanetary grains (Divine, 1993, J. Geophys. Res. 98, 17029). Furthermore, a rate of 6 impacts of grains with md>=10-13 kg during 107 days is in good agreement with the predictions of the interplanetary dust environment model by Staubach et al. (1997, Adv. Space Res. 19, 301). This result demonstrates that charge detectors as the CDA QP system offer a reliable in-situ technique for determining simultaneously both the mass and velocity of big interplanetary grains. The primary CDA subsystem to determine md and vd, however, is an impact ionisation detector. The majority of the 37 recorded dust impacts produced impact charges are well outside the calibrated range. Moreover, these impacts were usually characterised by impact ionisation signals which differ significantly from signals taken in calibration experiments. In this paper we took advantage of the fact that the measurement of Qd is not affected by the subsequent impact of the grain with the detector. By relating md and vd derived from Qd of the 6 QP impactors to their corresponding ionisation signals we show that in many cases even for energetic impacts outside the calibrated range meaningful values for the dust mass can be obtained. The observed deviations of the ionisation signals from the calibration measurements are likely due to the large amount of plasma generated by such impacts. We discuss the implications of these findings on a meaningful reduction of impact ionisation signals caused by big particle impacts. A new scheme to identify and to evaluate such signals is presented. These finding are of great importance for future Cassini measurements in the saturnian system.

Affiliated with

Also associated with

No associations

Rating

Cassini between Earth and asteroid belt: first in-situ charge measurements of interplanetary grains does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.

If you have personal experience with Cassini between Earth and asteroid belt: first in-situ charge measurements of interplanetary grains, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Cassini between Earth and asteroid belt: first in-situ charge measurements of interplanetary grains will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFWR-SCP-O-845660