[Paper Review] Three years of Ulysses dust data: 1993 to 1995

Harald Krüger, E. Grün+19 more|arXiv (Cornell University)|Sep 10, 1998

Astro and Planetary Science29 references4 citations

TL;DR

This paper presents a comprehensive analysis of 509 dust particle impacts detected by the Ulysses spacecraft's dust detector between 1993 and 1995, covering heliocentric distances from 1.3 AU to 5.4 AU and inclinations up to 79°. It confirms a stable interstellar dust flux of ~0.4 impacts per day, identifies two distinct interplanetary dust populations—micrometer-sized particles near the ecliptic and sub-micrometer particles at high latitudes—and validates a model of interstellar dust flux with good agreement.

ABSTRACT

The Ulysses spacecraft is orbiting the Sun on a highly inclined ellipse ($i = 79^{\circ}$). After its Jupiter flyby in 1992 at a heliocentric distance of 5.4 AU, the spacecraft reapproached the inner solar system, flew over the Sun's south polar region in September 1994, crossed the ecliptic plane at a distance of 1.3 AU in March 1995, and flew over the Sun's north polar region in July 1995. We report on dust impact data obtained with the dust detector onboard Ulysses between January 1993 and December 1995. We publish and analyse the complete data set of 509 recorded impacts of dust particles with masses between $10^{-16}$ g to $10^{-7}$ g. Together with 968 dust impacts from launch until the end of 1992 published earlier (Grün et al., 1995, {\em Planet. Space Sci}, Vol. 43, p. 971-999), information about 1477 particles detected with the Ulysses sensor between October 1990 and December 1995 is now available. The impact rate measured between 1993 and 1995 stayed relatively constant at about 0.4 impacts per day and varied by less than a factor of ten. Most of the impacts recorded outside about 3.5 AU are compatible with particles of interstellar origin. Two populations of interplanetary particles have been recognised: big micrometer-sized particles close to the ecliptic plane and small sub-micrometer-sized particles at high ecliptic latitudes. The observed impact rate is compared with a model for the flux of interstellar dust particles which gives relatively good agreement with the observed impact rate. No change in the instrument's noise characteristics or degradation of the channeltron could be revealed during the three-year period.

Motivation & Objective

• To analyze the complete set of dust impact data collected by the Ulysses dust detector from January 1993 to December 1995.
• To determine the spatial and temporal distribution of interplanetary and interstellar dust particles in the inner solar system.
• To assess the consistency of the dust detector’s performance over three years, ruling out instrument degradation or noise changes.
• To compare observed dust impact rates with theoretical models of interstellar dust flux.

Proposed method

• The Ulysses spacecraft's dust detector recorded impacts of dust particles with masses between 10⁻¹⁶ g and 10⁻⁷ g during its highly inclined solar orbit.
• The data set of 509 impacts from 1993–1995 was combined with 968 earlier impacts (1990–1992) to form a total of 1477 detections.
• Impact rates were analyzed as a function of heliocentric distance and ecliptic latitude to distinguish between interplanetary and interstellar dust populations.
• A model of interstellar dust flux was applied and compared with observed impact rates to validate the detection of interstellar dust.
• Instrument stability was assessed by monitoring noise characteristics and channeltron degradation over time.
• Data were processed using rotating packages and LaTeX 2e for publication-quality formatting and analysis.

Experimental results

Research questions

• RQ1 What is the temporal and spatial distribution of dust particle impacts detected by Ulysses between 1993 and 1995?
• RQ2 Are the observed dust impacts consistent with interstellar dust flux, and how do they vary with heliocentric distance and ecliptic latitude?
• RQ3 Can the observed impact rate be explained by existing theoretical models of interstellar dust flux?
• RQ4 Are there two distinct populations of interplanetary dust particles, as suggested by their size and distribution?
• RQ5 Has the dust detector’s performance degraded or changed significantly over the three-year observation period?

Key findings

• The dust impact rate remained relatively constant at approximately 0.4 impacts per day between 1993 and 1995, with variations less than a factor of ten.
• Most dust impacts recorded at heliocentric distances beyond 3.5 AU are consistent with interstellar dust particles.
• Two distinct populations of interplanetary dust were identified: larger micrometer-sized particles near the ecliptic plane and smaller sub-micrometer-sized particles at high ecliptic latitudes.
• The observed impact rate of interstellar dust shows good agreement with a theoretical model of interstellar dust flux.
• No significant changes in instrument noise or degradation of the channeltron were detected over the three-year period.
• The combined data set of 1477 dust impacts (1990–1995) provides a robust statistical basis for studying the dynamics and origin of dust in the inner solar system.