Interstellar Dust in the Solar System: Model versus In-Situ Spacecraft Data

In the early 1990s, contemporary interstellar dust penetrating deep into the heliosphere was identified with the in-situ dust detector on board the Ulysses spacecraft. Later on, interstellar dust was also identified in the data sets measured with dust instruments on board Galileo, Cassini and Helios. Ulysses monitored the interstellar dust stream at high ecliptic latitudes for about 16 years. The three other spacecraft data sets were obtained in the ecliptic plane and cover much shorter time intervals.We compare in-situ interstellar dust measurements obtained with these four spacecrafts, published in the literature, with predictions of a state-of-the-art model for the dynamics of interstellar dust in the inner solar system (Interplanetary Meteoroid environment for EXploration, IMEX), in order to test the reliability of the model predictions. Micrometer and sub-micrometer sized dust particles are subject to solar gravity and radiation pressure as well as to the Lorentz force on a charged dust particle moving through the Interplanetary Magnetic Field. The IMEX model was calibrated with the Ulysses interstellar dust measurements and includes these relevant forces. We study the time-resolved flux and mass distribution of interstellar dust in the solar system. The IMEX model agrees with the spacecraft measurements within a factor of 2 to 3, also for time intervals and spatial regions not covered by the original model calibration with the Ulysses data set. It usually underestimates the dust fluxes measured by the space missions which were not used for the model calibration, i.e. Galileo, Cassini and Helios. IMEX is a unique time-dependent model for the prediction of interstellar dust fluxes and mass distributions for the inner and outer solar system. The model is suited to study dust detection conditions for past and future space missions.Comment: 24 pages, 7 figures, 1 tabl

Heliospheric modulation of the interstellar dust flow on to Earth

Aims. Based on measurements by the Ulysses spacecraft and high-resolution modelling of the motion of interstellar dust (ISD) through the heliosphere we predict the ISD flow in the inner planetary system and on to the Earth. This is the third paper in a series of three about the flow and filtering of the ISD. Methods. Micrometer- and sub-micrometer-sized dust particles are subject to solar gravity and radiation pressure as well as to interactions with the interplanetary magnetic field that result in a complex size-dependent flow pattern of ISD in the planetary system. With high-resolution dynamical modelling we study the time-resolved flux and mass distribution of ISD and the requirements for detection of ISD near the Earth. Results. Along the Earth orbit the density, speed, and flow direction of ISD depend strongly on the Earth's position and the size of the interstellar grains. A broad maximum of the ISD flux (2x10^{-4}/m^2/s of particles with radii >~0.3\mu m) occurs in March when the Earth moves against the ISD flow. During this time period the relative speed with respect to the Earth is highest (~60 km/s), whereas in September when the Earth moves with the ISD flow, both the flux and the speed are lowest (<~10 km/s). The mean ISD mass flow on to the Earth is ~100 kg/year with the highest flux of ~3.5kg/day occurring for about 2 weeks close to the end of the year when the Earth passes near the narrow gravitational focus region downstream from the Sun. The phase of the 22-year solar wind cycle has a strong effect on the number density and flow of sub-micrometer-sized ISD particles. During the years of maximum electromagnetic focussing (year 2031 +/- 3) there is a chance that ISD particles with sizes even below 0.1\mu m can reach the Earth. Conclusions. We demonstrate that ISD can be effectively detected, analysed, and collected by space probes at 1 AU distance from the Sun.Comment: 17 pages, 17 figure

Effects of neighbouring planets on the formation of resonant dust rings in the inner Solar System

Context. Findings by the Helios and STEREO mission have indicated the presence of a resonant circumsolar ring of dust associated with Venus. Attempts to model this phenomenon as an analogue to the resonant ring of Earth - as a result of migrating dust trapped in external mean-motion resonances (MMRs) - have so far been unable to reproduce the observed dust feature. Other theories of origin have recently been put forward. However, the reason for the low trapping efficiency of Venus's external MMRs remains unclear. Aims. Here we look into the nature of the dust trapping resonant phenomena that arise from the multi-planet configuration of the inner Solar System, aiming to add to the existent understanding of resonant dust rings in single planet systems. Methods. We numerically modelled resonant dust features associated with the inner planets and specifically looked into the dependency of these structures and the trapping efficiency of particular resonances on the configuration of planets. Results. Besides Mercury showing no resonant interaction with the migrating dust cloud, we find Venus, Earth, and Mars to considerably interfere with each other's resonances, influencing their ability to form circumsolar rings. We find that the single most important reason for the weakness of Venus's external MMR ring is the perturbing influence of its outer neighbour - Earth. In addition, we find Mercury and Mars to produce crescent-shaped density features, caused by a directed apsidal precession occurring in particles traversing their orbital region

Counter Data of the Cosmic Dust Analyzer aboard the Cassini spacecraft and possible "dust clouds" at Saturn

We present the impact rates of dust particles recorded by the Cosmic Dust Analyzer (CDA) aboard the Cassini spacecraft. The "dust counters" evaluate the quality of an impact and give rise to the apparent density of dust particles in space. The raw data is pre-selected and refined to a new structure that serves to a better investigation of densities, flows, and properties of interplanetary dust grains. Our data is corrected for the dead time of the instrument and corresponds to an assumed Kepler orbit (pointing of the sensitive area). The processed data are published on the website for the Magnetosphere and Plasma Science (MAPSview), where it can be correlated with other Cassini instruments. A sample is presented for the Titan flyby on DOY 250/2006. We find that the dust density peaks at two times, at least, in a void region between Titan and Rhea. Such features may point to extended clouds of small particles drifting slowly in space. These density clouds seem to be stable for as long as several months or few years before dispersing.Comment: 16 pages, 5 figure

Techniques for Galactic Dust Measurements in the Heliosphere

Galactic interstellar dust (ISD) is the major ingredient in planetary formation. However, information on this important material has been extremely limited. Recently the Ulysses dust detector has identified and measured interstellar dust outside 1.8~AU from the Sun at ecliptic latitudes above $50^{\circ}$. Inside this distance it could not reliably distinguish interstellar from interplanetary dust. Modeling the Ulysses data suggests that up to 30 % of dust flux with masses above $10^{-16}\rm kg$ at 1~AU is of interstellar origin. From the Hiten satellite in high eccentric orbit about the Earth there are indications that ISD indeed reaches the Earth's orbit. Two new missions carrying dust detectors, Cassini and Stardust, will greatly increase our observational knowledge. In this paper we briefly review instruments used on these missions and compare their capabilities. The Stardust mission [{\em Brownlee et al.}, 1996] will analyze the local interstellar dust population by an in-situ chemical analyzer and collect ISD between 2 and 3~AU from the Sun. The dust analyzer on the Cassini mission will determine the interstellar dust flux outside Venus' orbit and will provide also some compositional information. Techniques to identify the ISD flux levels at 1~AU are described that can quantify the interstellar dust flux in high-Earth orbit (outside the debris belts) and provide chemical composition information of galactic dust.Comment: Accepted for Journal of Geophysical Research, 6 figures, Late

Micrometeoroid infall onto Saturn’s rings constrains their age to no more than a few hundred million years

There is ongoing debate as to whether Saturn’s main rings are relatively young or ancient— having been formed shortly after Saturn or during the Late Heavy Bombardment. The rings are mostly water-ice but are polluted by non-icy material with a volume fraction ranging from ∼0.1 to 2%. Continuous bombardment by micrometeoroids exogenic to the Saturnian system is a source of this non-icy material. Knowledge of the incoming mass flux of these pollutants allows estimation of the rings’ exposure time, providing a limit on their age. Here we report the final measurements by Cassini’s Cosmic Dust Analyzer of the micrometeoroid flux into the Saturnian system. Several populations are present, but the flux is dominated by low-relative velocity objects such as from the Kuiper belt. We find a mass flux between 6.9 · 10−17 and 2.7 · 10−16 kg m−2s−1 from which we infer a ring exposure time ≲100 to 400 million years in support of recent ring formation scenarios

The production of platinum-coated silicate nanoparticle aggregates for use in hypervelocity impact experiments

We present a method for producing metal-coated low-density (?3) aggregate silicate dust particles for use in hypervelocity impact (HVI) experiments. Particles fabricated using the method are shown to have charged and electrostatically accelerated in the Max Planck Institut für Kernphysik (MPI-K) 2 MV Van de Graaff accelerator, allowing the production of impact ionization mass spectra of silicate particles (impacting at velocities ranging from ?1 to >30 km s?1, corresponding to sizes of >1 ?m to <0.1 ?m) using the Large Area Mass Analyser (LAMA) instrument, designed for cosmic dust detection in space. Potential uses for the coated grains, such as in the calibration of aerogel targets similar to those used on the Stardust spacecraft, are also discussed