We constrain the inventory of exogenic dust populations found in the Saturn system by analysing 14 yr of Cassini Cosmic Dust Analyzer (CDA) data acquired since Saturn orbit insertion. Our analysis reveals that the Saturn system is permanently traversed by exogenic dust coming from the surrounding interplanetary space, interplanetary dust particles (IDPs), and from the interstellar medium, interstellar dust (ISD). The CDA data give a first in situ experimental insight into the different dust populations of the outer Solar system and their relative abundances. We observe a population of sub-micron to tens of micron-sized interplanetary grains, with low injection speed at Saturn's Hill's boundary, and whose dynamical signature supports their collisional origin in the Edgeworth Kuiper belt or a release upon cometary activity of Jupiter-family comets and Centaurs. We confirm that those populations are the most abundant IDP population in the Saturn system, participating to the weathering of the surfaces of the icy moons and the rings. We also observe the signature of sub-micron grains with high injection speeds at Saturn's Hill's radius, bearing the dynamical signature of dust released by Oort cloud comets. In addition, a population of large ISD grains appears clearly in our data, in the micrometre-sized regime, hence larger than detected in situ by previous missions and analysis. Finally, we also find hints of an extended dust halo of bound particles, reaching high latitudes in the inner Saturn system as well as possible sporadic sources of interplanetary grains.

During the Grand Finale orbits, Cassini's Cosmic Dust Analyzer (CDA) recorded in situ mass spectra of ice and mineral nanodust grains ejected from Saturn's main rings falling into the planet's atmosphere. We present a compositional analysis of the mineral dust fraction employing a spectral deconvolution method to determine the elemental composition of these grains. The results indicate a relatively homogenous composition of exclusively Mg-rich silicates, with Mg, Si, and Ca close to CI chondritic abundances but a significant depletion in Fe and only traces of organic material at best. The Fe depletion becomes even more pronounced when compared to Fe-rich interplanetary dust particles encountered by CDA in the Saturnian system, which are assumed to contaminate and darken the main rings over time. We discuss potential explanations for the depletion, from which we favour compositional alteration of the infalling dust grains by impact-triggered chemistry in combination with dynamical selection effects and instrumental bias as the most plausible ones. This might cause an accumulation of Fe in the main rings over time, most likely in the form of oxides.

The DESTINY+(Demonstration and Experiment of Space Technology for INterplanetary voYage with Phaethon fLyby and dUst Science) Dust Analyser (DDA) is a state-of-the-art dust telescope for the in situ analysis of cosmic dust particles. As the primary scientific payload of the DESTINY+ mission, it serves the purpose of characterizing the dust environment within the Earth-Moon system, investigating interplanetary and interstellar dust populations at 1 AU from the Sun and studying the dust cloud enveloping the asteroid (3200) Phaethon. DDA features a two-axis pointing platform for increasing the accessible fraction of the sky. The instrument combines a trajectory sensor with an impact ionization time-of-flight mass spectrometer, enabling the correlation of dynamical, physical and compositional properties for individual dust grains. For each dust measurement, a set of nine signals provides the surface charge, particle size, velocity vector, as well as the atomic, molecular and isotopic composition of the dust grain. With its capabilities, DDA is a key asset in advancing our understanding of the cosmic dust populations present along the orbit of DESTINY+. In addition to providing the scientific context, we are presenting an overview of the instrument's design and functionality, showing first laboratory measurements and giving insights into the observation planning. This article is part of a theme issue 'Dust in the Solar System and beyond'.

The selected ice nanoparticle accelerator, SELINA, was used to prepare beams of single ice particles with positive or negative charge. Positively charged particles were prepared from deionized water and 0.05–0.2 molar solutions of sodium chloride in water, and negatively charged ice particles were generated from water without salt. Depending on the electrospray source configuration, the measured particles vary from 50 to 1000 nm in diameter. The kinetic energy per charge for all particles was set to 200 eV by the collisional equilibration in quadrupoles, which resulted in primary velocities up to 600 m/s for the lowest m/z particles. The electrospray ionization and thus particle formation from SELINA become less efficient with increasing salt concentration, resulting in a lower detected particle frequency and size. Good instrument operation is achievable for concentrations below 0.2 M. After we have verified and characterized positively and negatively charged ice particles, we have combined SELINA with a target and time-of-flight spectrometer for a ‘proof-of-principle’ post acceleration of 120 nm particles towards hypervelocity ( v ~ 3000 m/s) and detection of fragments from the particle impact (SELINA-HIMS). General conditions are discussed for the acceleration of particles between 50 and 1000 nm to velocities well above 3000 m/s with SELINA-HIMS instrument. This article is part of the theme issue ‘Dust in the Solar System and beyond’.

Saturn’s moon Enceladus harbours a global 1 ice-covered water ocean 2,3 . The Cassini spacecraft investigated the composition of the ocean by analysis of material ejected into space by the moon’s cryovolcanic plume 4–9 . The analysis of salt-rich ice grains by Cassini’s Cosmic Dust Analyzer 10 enabled inference of major solutes in the ocean water (Na + , K + , Cl – , HCO 3 – , CO 3 2– ) and its alkaline pH 3,11 . Phosphorus, the least abundant of the bio-essential elements 12–14 , has not yet been detected in an ocean beyond Earth. Earlier geochemical modelling studies suggest that phosphate might be scarce in the ocean of Enceladus and other icy ocean worlds 15,16 . However, more recent modelling of mineral solubilities in Enceladus’s ocean indicates that phosphate could be relatively abundant 17 . Here we present Cassini’s Cosmic Dust Analyzer mass spectra of ice grains emitted by Enceladus that show the presence of sodium phosphates. Our observational results, together with laboratory analogue experiments, suggest that phosphorus is readily available in Enceladus’s ocean in the form of orthophosphates, with phosphorus concentrations at least 100-fold higher in the moon’s plume-forming ocean waters than in Earth’s oceans. Furthermore, geochemical experiments and modelling demonstrate that such high phosphate abundances could be achieved in Enceladus and possibly in other icy ocean worlds beyond the primordial CO 2 snowline, either at the cold seafloor or in hydrothermal environments with moderate temperatures. In both cases the main driver is probably the higher solubility of calcium phosphate minerals compared with calcium carbonate in moderately alkaline solutions rich in carbonate or bicarbonate ions.

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 −2 s −1 from which we infer a ring exposure time ≲100 to 400 million years in support of recent ring formation scenarios.

Saturn's large and diffuse E ring is populated by microscopic water ice dust particles, which originate from the Enceladus plume. Cassini's Cosmic Dust Analyser sampled these ice grains, revealing three compositional particle types with different concentrations of salts and organics. Here, we present the analysis of CDA mass spectra from several orbital periods of Cassini, covering the region from interior to Enceladus' orbit to outside the orbit of Rhea, to map the distribution of the different particle types throughout the radial extent of the E ring. This will provide a better understanding of the potential impact of space weathering effects on to these particles, as the ice grains experience an increasing exposure age during their radially outward migration. In this context, we report the discovery of a new ice particle type (Type 5), which produces spectra indicative of very high salt concentrations, and which we suggest to evolve from less-salty Enceladean ice grains by space weathering. The radial compositional profile, now encompassing four particle types, reveals distinct radial variations in the E ring. At the orbital distance of Enceladus our results are in good agreement with earlier compositional analyses of E ring ice grains in the moon's vicinity. With increasing radial distance to Saturn however, our analysis suggests a growing degree of space weathering and considerable changes to the spatial distribution of the particle types. We also find that the proportion of Type 5 grains - peaking near Rhea's orbit - probably reflects particle charging processes in the E ring.

To assess the potential habitability of Jupiter's moon Europa, it is important to understand its chemical composition (Hand et al., 2007). Young terrain features on Europa's surface likely consist of material up-welled from the liquid water source below (Wilson et al., 1997; Pappalardo et al., 1998; McCord et al., 1999; Figueredo and Greeley, 2004; Mevel and Mercier, 2007), encoding relevant compositional information. A major science objective of NASA's Europa Clipper mission is to characterize the composition of young terrain features using data acquired on close flybys. The Surface Dust Analyzer (SUDA) is an in situ instrument that collects and analyzes the composition of individual grains (Kempf et al., 2012), which are ejected from Europa's surface by a continuous bombardment of interplanetary impactors (Kruger et al., 1999, 2003; Goode et al., 2021). By applying a dynamical model of these particles, we compute the probability of SUDA's detections originating from a given feature along the flyby trajectory based on Monte Carlo (MC) simulations. The time-of-flight (TOF) mass spectra that characterize the chemical composition of individual grains, results in a time series of various compositional types along the flyby. We present here a method to analyze a time series of compositional spectra recorded by SUDA that provides a robust estimate for the abundance of compositional types on the surface, spatially resolved for features along the ground track of the flyby. By demonstrating the association of compositional detections with geological sites of origin, data collected by SUDA can be used to infer the compositional ground truth for terrain features on Europa.

To assess the potential habitability of Europa, it is important to understand its chemical composition (Hand et al., 2007). Young terrain features on Europa’s surface likely consist of material up-welled from the liquid water source below (Wilson et al., 1997; Pappalardo et al., 1998; McCord et al., 1999; Figueredo and Greeley, 2004; Mével and Mercier, 2007), encoding relevant compositional information. A major science objective of NASA’s Europa Clipper mission is to characterize the composition of young terrain features using data acquired on close flybys. The Surface Dust Analyzer (SUDA) is an in situ instrument that collects and analyzes the composition of individual grains (Kempf et al., 2012), which are ejected from Europa’s surface by a continuous bombardment of interplanetary impactors (Krüger et al., 1999, 2003; Goode et al., 2021). By applying a dynamical model to these particles, we compute the probability of SUDA’s detections originating from a given feature along the flyby trajectory based on Monte Carlo (MC) simulations. The time-of-flight (TOF) mass spectra that characterizes the chemical composition of individual grains results in a time series of various compositional types along the flyby. We present here a method to analyze a time series of compositional spectra recorded by SUDA that provides a robust estimate for the abundance of different compositional types on the surface, resolved for features along the ground track of the flyby. By demonstrating the association of compositional detections with geological sites of origin, data collected by SUDA is used to infer the compositional ground truth for young terrain features on Europa.

Aims. An asymmetric dust cloud was detected around the Moon by the Lunar Dust Experiment on board the Lunar Atmosphere and Dust Environment Explorer mission. We investigate the dynamics of the grains that escape the Moon and their configuration in the Earth-Moon system. Methods. We use a plausible initial ejecta distribution and mass production rate for the ejected dust. Various forces, including the solar radiation pressure and the gravity of the Moon, Earth, and Sun, are considered in the dynamical model, and direct numerical integrations of trajectories of dust particles are performed. The final states, the average life spans, and the fraction of retrograde grains as functions of particle size are computed. The number density distribution in the Earth-Moon system is obtained through long-term simulations. Results. The average life spans depend on the size of dust particles and show a rapid increase in the size range between 1 and 10 μm. About 3.6 × 10 −3 kg s −1 (~2%) particles ejected from the lunar surface escape the gravity of the Moon, and they form an asymmetric torus between the Earth and the Moon in the range [10 R E , 50 R E ], which is offset toward the direction of the Sun. A considerable number of retrograde particles occur in the Earth-Moon system.

Measurements during the final phase of the Cassini mission revealed the composition of individual dust particles, ejected by micrometeoroid impacts from Saturn’s main rings. These measurements were conducted with the in situ time-of-flight mass spectrometer of the Cosmic Dust Analyzer (CDA) [1] during the close planet encounters of the Grand Finale Orbits from April to September of 2017.Here we present the compositional analysis of silicate bearing nanoparticles (about 20–100 nm in radius), that, according to our dynamical models [2], are ejected mainly from the B and C rings by micrometeoroid impacts. With an observed ice-to-silicate particle ratio of 2:1 [2], we see a much higher silicate abundance in these ring segments, compared to values constrained by remote sensing techniques [3,4,5].In order to assess the elemental composition of individual particles, application of a deconvolution technique to the CDA mass spectra is required. This technique is based on an approach to constrain the composition of Interstellar Dust Particles (ISDs), also detected with CDA [6]. After application of the deconvolution and Relative Sensitivity Factors (RSFs) [7], elemental abundances for the individual particles are derived.We find Mg, Si and Ca similar to cosmic abundances (ISD and CI chondritic). Fe, however, is significantly depleted, for the Fe/Mg ratio on average by a factor of 2.3 compared to cosmic abundances. This observation contrasts with Fe-rich (≈ 5 w.r.t. cosmic abundances) exogenous material (IDPs), observed in the Saturnian system by CDA [8]. This drastic discrepancy in composition between ring silicates and IDPs at Saturn seems difficult to reconcile with IDPs being the main factor in polluting and darkening the rings over time [4,5,9,10]. We review several scenarios, how these compositional differences could be explained.References[1] R. Srama et al. (2004), Space Science Reviews 114, 465–518.[2] H.-W. Hsu et al. (2018), Science 362.[3] E. Epstein et al. (1984), Icarus 58, 403–411.[4] Zhang et al. (2017a), Icarus 281, 297–321.[5] Zhang et al. (2017b), Icarus 294, 14–42.[6] N. Altobelli et al. (2016), Science 352, 312–318.[7] K. Fiege et al. (2014), Icarus 241, 336–345.[8] C. Fischer et al. (2022), this conference.[9] J. Cuzzi and P. Estrada (1998), Icarus 132, 1–35.[10] J. Cuzzi et al. (2009), Springer, Dordrecht, 459–509.

<p>Europa Clipper, NASA’s next flagship mission launching in 2024, will closely study Jupiter’s icy ocean moon in order to determine if it has conditions favorable for life. Among the nine scientific instruments will be the Surface Dust Analyzer (SUDA), a state-of-the-art instrument for in situ chemical analysis of dust grains. During a series of close flybys of Europa (~25 to 100 km at closest approach), SUDA will collect and measure the chemical composition of thousands of ice and dust particles ranging from ~200 nm to 100 microns in radius, which will be direct samples from Europa’s surface. This is possible due to the flux of interplanetary micrometeoroids impacting the surface producing a cloud of ejecta particles, which SUDA detects and analyzes. Knowing the spacecraft trajectory, instrument pointing, and particle velocity through the instrument aperture, SUDA’s in situ chemical measurements will be linked to their site of origin on Europa’s surface near the spacecraft ground-track, thereby offering geological context for chemical composition. This method implements established models of impact ejecta dynamics and derives distributions for each measurement’s site of origin on the surface using Monte Carlo simulations. These studies are especially useful for evaluating the science return for particular tour designs since we can simulate SUDA’s effectiveness at mapping the composition of geologically interesting areas. With well targeted flybys by Europa Clipper, SUDA will be help constrain the chemical composition of surface material originating from various geological features, particularly those characterized by non-icy materials. This will enhance our understanding of the exchange processes between the icy surface and subsurface ocean as well as assess the habitability of Europa.</p>

We analyze systems of clusters and interacting upon colliding-a collision between two clusters may lead to merging or fragmentation-and we also investigate the influence of additional spontaneous fragmentation events. We consider both closed systems in which the total mass remains constant and open systems driven by a source of small-mass clusters. In closed systems, the size distribution of aggregates approaches a steady state. For these systems the relaxation time and the steady state distribution are determined mostly by spontaneous fragmentation while collisional fragmentation plays a minor role. For open systems, in contrast, the collisional fragmentation dominates. In this case, the system relaxes to a quasi-stationary state where cluster densities linearly grow with time, while the functional form of the cluster size distribution persists and coincides with the steady state size distribution of a system which has the same aggregation and fragmentation rates and only collisional fragmentation.

Aims. The surfaces of the Trojan asteroids are steadily bombarded by interplanetary micrometeoroids, which releases ejecta of small dust particles. These particles form the faint dust arcs that are associated with asteroid clouds. Here we analyze the particle dynamics and structure of the arc in the region of the $L_4$ Trojan asteroids. Methods. We calculate the total cross section of the $L_4$ Trojan asteroids and the production rate of dust particles. The motion of the particles is perturbed by a variety of forces. We simulate the dynamical evolution of the dust particles, and explore the overall features of the Trojan dust arc. Results. The simulations show that the arc is mainly composed of grains in the size range 4-10 microns. Compared to the $L_4$ Trojan asteroids, the dust arc is distributed more widely in the azimuthal direction, extending to a range of [30,120] degrees relative to Jupiter. The peak number density does not develop at $L_4$. There exist two peaks that are azimuthally displaced from $L_4$.

In this paper we analyze the dynamical behavior of large dust grains in the vicinity of a cometary nucleus. To this end we consider the gravitational field of the irregularly shaped body, as well as its electric and magnetic fields. Without considering the effect of gas friction and solar radiation, we find that there exist grains which are static relative to the cometary nucleus; the positions of these grains are the stable equilibria. There also exist grains in the stable periodic orbits close to the cometary nucleus. The grains in the stable equilibria or the stable periodic orbits won't escape or impact on the surface of the cometary nucleus. The results are applicable for large charge dusts with small area-mass ratio which are near the cometary nucleus and far from the Solar. It is found that the resonant periodic orbit can be stable, and there exist stable non-resonant periodic orbits, stable resonant periodic orbits and unstable resonant periodic orbits in the potential field of cometary nuclei. The comet gravity force, solar gravity force, electric force, magnetic force, solar radiation pressure, as well as the gas drag force are all considered to analyze the order of magnitude of these forces acting on the grains with different parameters. Let the distance of the dust grain relative to the mass centre of the cometary nucleus, the charge and the mass of the dust grain vary, respectively, fix other parameters, we calculated the strengths of different forces. The motion of the dust grain depends on the area-mass ratio, the charge, and the distance relative to the comet's mass center. For a large dust grain (> 1 mm) close to the cometary nucleus which has a small value of area-mass ratio, the comet gravity is the largest force acting on the dust grain. For a small dust grain (< 1 mm) close to the cometary nucleus with large value of area-mass ratio, both the solar radiation pressure and the comet gravity are two major forces. If the a small dust grain which is close to the cometary nucleus have the large value of charge, the magnetic force, the solar radiation pressure, and the electric force are all major forces. When the large dust grain is far away from the cometary nucleus, the solar gravity and solar radiation pressure are both major forces.

The structure of Enceladus׳ south polar plume of charged dust is studied by simulations of the dust grain dynamics. The model considers the Lorentz force and charging of the grains by the plasma environment within the plume. Simulated dust plumes are investigated by applying 10 selected sets of dust parameters that include variations of the grain production rate, the slope of the grain size distribution and the start conditions (velocity, direction) of the grains. The modeled dust plume profiles are in good agreement with nanograin data of Cassini Plasma Spectrometer (CAPS). Major results are (1) due to the local plasma environment the nanograins are accelerated by the Lorentz force and form a structured tail; (2) due to the finite charging time the peak dust charge density is located about 0.3–0.6rE below Enceladus׳ south pole; (3) nanograins smaller than 10nm are more than 99% of the produced dust; (4) CAPS data are best matched if the nanograins are launched with high, collimated start velocities; (5) the grain charging time is crucially affected by inhomogeneities in the local plasma environment.

We propose a simple theoretical model for aggregative and fragmentative collisions in Saturn's dense rings. In this model the ring matter consists of a bimodal size distribution: large (meter sized) boulders and a population of smaller particles (tens of centimeters down to dust). The small particles can adhesively stick to the boulders and can be released as debris in binary collisions of their carriers. To quantify the adhesion force we use the JKR theory (Johnson, K., Kendall, K., Roberts, A. [1971]. Proc. R. Soc. Lond. A 324, 301-313). The rates of release and adsorption of particles are calculated, depending on material parameters, sizes, and plausible velocity dispersions of carriers and debris particles. In steady state we obtain an expression for the amount of free debris relative to the fraction still attached to the carriers. In terms of this conceptually simple model a paucity of subcentimeter particles in Saturn's rings (French, R.G., Nicholson, P.D. [2000]. Icarus 145, 502-523; Marouf, E. et al. [2008]. Abstracts for "Saturn after Cassini-Huygens" Symposium, Imperial College London, UK, July 28 to August 1, p. 113) can be understood as a consequence of the increasing strength of adhesion (relative to inertial forces) for decreasing particle size. In this case particles smaller than a certain critical radius remain tightly attached to the surfaces of larger boulders, even when the boulders collide at their typical speed. Furthermore, we find that already a mildly increased velocity dispersion of the carrier-particles may significantly enhance the fraction of free debris particles, in this way increasing the optical depth of the system. (C) 2011 Elsevier Inc. All rights reserved.

Classical methods to analyze the surface composition of atmosphereless planetary objects from an orbiter are IR and gamma ray spectroscopy and neutron backscatter measurements. The idea to analyze surface properties with an in-situ instrument has been proposed by Johnson et al. (1998). There, it was suggested to analyze Europa's thin atmosphere with an ion and neutral gas spectrometer. Since the atmospheric components are released by sputtering of the moon's surface, they provide a link to surface composition. Here we present an improved, complementary method to analyze rocky or icy dust particles as samples of planetary objects from which they were ejected. Such particles, generated by the ambient meteoroid bombardment that erodes the surface, are naturally present on all atmosphereless moons and planets. The planetary bodies are enshrouded in clouds of ballistic dust particles, which are characteristic samples of their surfaces. In situ mass spectroscopic analysis of these dust particles impacting onto a detector of an orbiting spacecraft reveals their composition. Recent instrumental developments and tests allow the chemical characterization of ice and dust particles encountered at speeds as low as 1km/s and an accurate reconstruction of their trajectories. Depending on the sampling altitude, a dust trajectory sensor can trace back the origin of each analyzed grain with about 10km accuracy at the surface. Since the detection rates are of the order of thousand per orbit, a spatially resolved mapping of the surface composition can be achieved. Certain bodies (e.g., Europa) with particularly dense dust clouds, could provide impact statistics that allow for compositional mapping even on single flybys. Dust impact velocities are in general sufficiently high at orbiters about planetary objects with a radius >1000km and with only a thin or no atmosphere. In this work we focus on the scientific benefit of a dust spectrometer on a spacecraft orbiting Earth's Moon as well as Jupiter's Galilean satellites. This ‘dust spectrometer' approach provides key chemical and isotopic constraints for varying provinces or geological formations on the surfaces, leading to better understanding of the body's geological evolution.

Enceladus as an Active Moon; Bern, Switzerland, 14–18 June 2010; In commemoration of the fifth anniversary of the discovery of Enceladus's plumes, a group of about 2 dozen specialists gathered at the International Space Science Institute (ISSI) in Switzerland (http://www.issibern.ch/teams/ActiveEnceladus) with the goal of advancing understanding of the nature of Enceladus and its unusual phenomena. Speakers at the meeting noted that Enceladus is much more exciting than even their wildest expectations for it more than 20 years ago when the Cassini‐Huygens mission to Saturn was conceived, in the 1980s, several years after the Voyager flybys. Cassini revealed the surprising activity of the icy moon Enceladus, which is ejecting plumes of water vapor and ice grains from its anomalously warm south polar region. During the flyby of Enceladus on 17 February 2005, the Cassini magnetometer observed magnetic effects caused by Enceladus's plumes. Alerted by these stunning measurements, the Cassini investigators focused in on Enceladus during subsequent flybys and obtained the presently known facts about the plumes and the large south polar thermal anomaly.