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Enceladus’s subsurface global ocean (1) can be probed by sampling the gaseous and icy material the moon expels into its cryovolcanic plume and - even further out - into Saturn’s E ring (2,3,4,5). Hydrothermal outflows caused by tidal heating (4,5,6), together with rich organic chemistry (7,8) imply that the moon appears to be one of most habitable places in our solar system. Among the critical elements C, H, N, O, P and S that are considered to be essential for life, all except phosphorous have either been identified (5,7,8) or - in the case of sulfur - tentatively detected (9). Recent geochemical modelling claims that P will be severely depleted in ocean worlds and thus P could be a bottle neck for the emergence of life in subsurface oceans (10).Here we present results from a re-analysis of mass spectrometric data from Cassini’s Cosmic Dust Analyzer (CDA), showing proof of sodium-phosphate salts in ice grains originating from Enceladus’s subsurface ocean. We found a small number of ice grains whose spectra clearly indicate the presence of at least two sodium orthophosphates: Na3PO4 and Na2HPO4. These CDA spectra have been subsequently reproduced in the laboratory which enables the quantitative evaluation of CDA spectra (11). We infer phosphate concentrations in the Enceladus ocean in the order of a few mM, at least 100-times higher concentrations than in Earth’s ocean.We carried out geochemical experiments and calculations showing that such high phosphate abundances can be achieved in Enceladus, either at the cold seafloor or in hydrothermal environments with moderate temperatures. The driver enabling the abundant availability of phosphate is the high observed concentration of dissolved carbonate species, which shift phosphate-carbonate mineral equilibria toward dissolution of solid phosphates into Enceladus’ ocean. We show that interactions between chondritic rocks and CO2-rich fluids generally lead to conditions where dissolved phosphate concentrations tend to maximize. Therefore P-rich oceans would commonly occur in ocean worlds beyond in the outer Solar System beyond the CO2 snow line.These results demonstrate that Enceladus has a high availability of dissolved P, which is thus likely not a limiting factor for development of putative life on Enceladus and probably on other ocean worlds in the outer Solar System. Since phosphate plays many roles in organic synthesis (12), Enceladus and other icy bodies could moreover serve as natural analogs of P-rich environments on early Earth, where chemical evolution might have been promoted.1 Thomas et al., Icarus 264 (2016), 2 Postberg et al., Nature 459 (2009), 3 Postberg et al., Nature 474 (2011), 4 Hsu et al., Nature 519 (2015), 5 Waite et al., Science 356 (2017), 6 Choblet et al. , Nat Astron 1 (2017), 7 Postberg et al., Nature 558 (2018) , 8 Khawaja et al., MNRAS 489 (2019), 9 Postberg et al., ISBN: 9780816537075 (2018), 10 Lingam & Loeb, Astron. J., 2018., 11 Klenner et al., Rapid Commun Mass Spectrom 33 (2019), 12 Powner et al., Nature 459 (2009)

The origin of Saturn’s ring is still not known. There is an ongoing argument whether Saturn’s ring have been formed shortly after Saturn together with its satellites or they may actually be a recent phenomenon in the solar system. This possibility of young rings has been vigorously debated for nearly 40 years, since the Voyager flybys of Saturn. Over the years, the most powerful support for this hypothesis has turned out to be the puzzle of the rings’ nearly pure water ice composition – unique in the family of planetary rings – in spite of the constant hail of rocky-carbon meteoroids from outside the Saturn system. However, three major uncertainties have left the ‘young-ring’ hypothesis unproven. Two of these have already been resolved by the Cassini mission: the amount of non-icy material currently in the rings, and the total ring mass. The third main constraint is the mass flux of non-icy meteoroids falling onto the rings. Here we report on the measurement of the meteoroid mass flux into the Saturnian system obtained by the charge-sensitive entrance grid system (QP) of the Cosmic Dust Analyser (CDA) on the Cassini spacecraft. The determination mass flux of non-icy material coming into the Saturn system completes the trifecta of constraints that are required to strongly support a youthful ring system. We analyzed the full CDA data set acquired after Cassini’s arrival at Saturn in 2004. The CDA detections determine the incident particle orbits, and they come (surprisingly) not from comets as expected, but mostly from Kuiper Belt Objects (with at least one other population also apparent). This means that most of the particles have low speeds relative to Saturn and are strongly focused gravitationally, such that the flux at the rings is even larger than previously estimated. We have also found that the flux has a statistically significant upper size cutoff, meaning that our detection is robust to Cassini’s finite observation time.

We present the science planning tool for dust instrument observations that is currently under development within the DESTINY+ project. The JAXA-led DESTINY+ mission (Demonstration and Experiment of Space Technology for Interplanetary voyage Phaethon fLyby and dUst Science), set to launch in 2024, carries two camera instruments intended to study the active asteroid 3200 Phaethon during a flyby in 2028, as well as the Destiny+ Dust Analyzer (DDA), an impact ionization time-of-flight mass spectrometer which will sample Phaethon’s dust environment. During the 4-years voyage leading up to the flyby, DDA will also study interplanetary and interstellar dust particles as its second main science objective. For this phase, the science working team is preparing tools to produce suitable high-level science operations schedules.As DESTINY+ relies on solar-electric propulsion to expand its Earth orbit and ultimately reach interplanetary space, a highly dynamic spacecraft attitude is required to achieve an optimal thrust vector and illumination of the solar panels. To maintain some pointing autonomy, DDA has a dual-axis pointing mechanism, granting a coverage of 1pi solid angle. The dynamic attitude combined with the flexibility of a pointing mechanism warrants elaborate planning to optimize coverage of directional dust fluxes, such as interstellar dust. Here we present the DDA Observation Planning Environment (DOPE), which is a graphical tool for intuitive campaign design, including visualizations such as spacecraft orientation or instrument footprint. Under the hood DOPE uses the SPICE toolkit for all geometric or time calculations, thus import of SPICE kernels for spacecraft trajectory, attitude, and clock is required. Here we describe the DDA science planning process to provide a contextual frame for the tool and demonstrate its functionality with emphasis on the geometrical capabilities.

The return to the Moon pushed forward by space agencies as well as private companies around the world, has rekindled interest in the Lunar dust environment, which was identified as a major factor in spacecraft safety and reliability considerations during the Apollo missions. Orbiting the Moon from 2013 to 2014, the Lunar Atmosphere and Dust Environment Explorer (LADEE) gathered conclusive evidence for the existence of a permanent, asymmetric dust cloud around the Moon [1]. Micron-sized ejecta particles generated at impact of interplanetary meteoroids on the Lunar surface act as the main source of this high-altitude dust exosphere, which shows a variable density in dependence of annual meteoroid showers.Here we report on the development of a dynamic model for the lunar ejecta dust cloud. This model simulates cloud particles in a Monte-Carlo fashion, drawing on a combination of existing engineering models and results from hypervelocity impact experiments as model inputs: To emulate the influx of meteoroids we use the Interplanetary Meteoroid Environment Model 2 (IMEM2) [2], developed under ESA contract, as well as a comet stream model based on meteor shower zenith-hourly-rates [3, 4]. To determine angular, velocity, and size distributions of ejecta particles, we resort to three different methods: (1) We use the software Ansys Autodyn to numerically model ejecta particles generated at hypervelocity impacts. (2) Impact experiments with a light-gas gun have been conducted at the Harbin Institute of Technology, to derive ejecta distributions generated by bigger projectiles. (3) We intend to conduct hypervelocity impact experiments with lunar soil simulant at the electrostatic dust-accelerator facility at the University of Stuttgart. The novel experiment set-up, which uses a delay-line-detector to measure micron-sized ejecta particles has recently been verified [5]. Ultimately, the simulated dust ejecta cloud will be fitted to LADEE/LDEX data. This poster-presentation gives an overview of the project and its various modules.References:[1] Horányi, M., et al. "A permanent, asymmetric dust cloud around the Moon." Nature 522.7556 (2015): 324-326.[2] Soja, R. H., et al. "IMEM2: a meteoroid environment model for the inner solar system." Astronomy & Astrophysics 628 (2019): A109.[3] Jenniskens, Peter. "Meteor stream activity I. The annual streams." Astronomy and Astrophysics 287 (1994): 990-1013.[4] McBride, Neil. "The importance of the annual meteoroid streams to spacecraft and their detectors." Advances in Space Research 20.8 (1997): 1513-1516.[5] Li, Yanwei, et al. "Measurement of fragments generated by hypervelocity impacts of micron-sized iron particles at grazing incidents." Advances in Space Research 69.6 (2022): 2629-2635.

Rare presolar grains originating by condensation in circumstellar atmospheres are known from meteorites [1]. These escaped processing in the solar nebula and are identified via their extremely diverse isotopic composition [1,2]. However, it is uncertain if such grains are representative for dust from the interstellar medium (ISM) [3–5], particular as [5] postulated a high fraction of interstellar grain population that formed directly in the ISM.In 1992 the Ulysses spacecraft discovered a dust flow from the Local Interstellar Cloud (LIC) [6]. During the Cassini mission at Saturn, the Cosmic Dust Analyser (CDA) could identify and analyse the chemical composition of 36 individual interstellar dust (ISD) particles [7]. These grains were distinguished from Saturn bound dust by their direction and high velocity. Their mean mass is consistent with the typical size [3-5] derived from astronomical observations. As major result, each individual ISD grain contains the major rock forming elements (Mg, Si, Fe, Ca) in roughly cosmic abundances, indicating compositional homogeneity at spatial scales as small as 100 nm. In contrast, CDA did neither detect carbon-rich grains such as graphite or SiC, nor pure metal grains (upper limit of 8% at the 2 sigma confidence level) [7].This homogeneity cannot be reconciled with isotopically and compositionally diverse populations of circumstellar dust inherited from AGB stars and supernovae found in meteorites. These grain populations consist mainly of silicates with a more diverse composition (e.g., olivine, pyroxene), however, also minor contributions (few %) of Al-oxides (e.g., corundum, hibonite), as well as carbonaceous grains (mainly silicon carbide) which contribute 20-50%, of the grains in the most primitive meteorites [2]. In contrast to circumstellar grains found in meteorites, the LIC-ISD grains detected by Cassini have a much lower variation of Mg/Si or Mg/Fe ratios [7], and appear to be a grain population homogenized by destruction, recondensation and equilibration processes in the ISM. This can be reconciled with astronomical observations of the diffuse ISM demonstrating that condensable elements of atomic mass >23 are depleted in the gas phase and hence bound in solids. Considering that the mean lifetime of ISD grains against destruction by supernova shocks is much shorter (c. 0.5 Ga) than the average residence time of ISM matter of 2.5 Ga [5], an origin of a high fraction of ISD by grain destruction followed by recondensation was suggested by [5,7]. While grain destruction most likely occurs in the hot interstellar medium, i.e., low-density cavities formed by supernova shock fronts, condensation likely occurs in the cold interstellar medium, i.e., cold molecular clouds which are also formation regions of stars and planets.The upcoming DESTINY+ mission [8] will be equipped with an improved impact ionization mass spectrometer, the DESTINY+ Dust Analyser (DDA). During the mission, hundreds of ISD particles are expected to be measured [9]), yielding high quality mass spectra with a resolution of c. 100-200 when compared to c. 20-50 of Cassini CDA [10]. This will allow much better resolution of mass peaks at 23-28 amu (Na, Mg, Al, Si) and 39-41 (K, Ca), particularly yielding improved constraints on abundances of Al and Si. This will allow, e.g., to distinguish between Mg silicates like pyroxene and olivine or Al-rich feldspar type silicates. Also, more precise values for Na and K can be expected, particularly as some of the Cassini CDA data were compromised by alkali contamination of the Rhodium target [7]. Furthermore, the higher number of ISD particle detections will allow to better quantify the ISD fraction of non-silicate particles (oxides, SiC, graphite, metal, see [1]). This will also provide constraints on dynamic forces acting on the ISD particle flux, particularly the question if high beta particles are preferentially deflected from the inner solar system by solar radiation forces. Finally, DDA measurements will also contribute to solve the problem of apparently low or “missing” organic components in CDA detected particles, which may be caused by volatilization of refractory organic material in ISD mantles upon entering the heliosphere [11].Hence, interstellar dust detections by the DESTINY+ Dust Analyser will likely improve our understanding of the chemical nature of interstellar dust, its processing and lifetime in various phases of the interstellar medium, possible processing and volatile loss upon traversing our solar system to 1 AU, flux modulations upon interaction with solar electromagnetic forces, and last but not least, a tight age constraint on the LIC dust. References:[1] E. Zinner (2014) In Meteorites and Cosmochemical Processes (ed. Davis A. M.). Elsevier, Amsterdam, pp. 181–213[2] J. Leitner, C. Vollmer, P. Hoppe, J. Zipfel (2012) Astrophysical Journal 745, 38[3] P. C. Frisch et al. (1999) Astrophysical Journal 525, 492[4] H. Kimura, I. Mann, E. K. Jessberger (2003) Astrophysical Journal 583, 314[5] S. Zhukovska, H.-P. Gail, M. Trieloff (2008) Astronomy & Astrophysics 479, 453[6] E. Grün et al. (1993) Nature 362, 428-430[7] N. Altobelli, F. Postberg, K. Fiege, M. Trieloff et al. (2016) Science 352, 312[8] H. Arai, M. Kobayashi, et al. (2018) Lun. Planet. Sci. Conf. 49, abstr. #2570[9] Krüger H., Strub P., et al. (2019) Planetary & Space Science 172, 22-42.[10] Srama R. et al. (2004) Space Science Reviews 114, 465-518. [11] H. Kimura, F. Postberg, N. Altobelli, M. Trieloff (2020) Astronomy & Astrophysics 643, A50

The surface of the Moon and other airless planetary bodies is usually covered by a regolith layer. The meteoroids and interplanetary dust particles bombarding such highly pulverized layer may excavate with a yield up to 1000 times of the impactor’s own mass. The excavated ejecta grains with relatively high speeds are the main components of the dust cloud around airless bodies. Faster grains with speeds exceeding the escape velocity of a planetary body contribute to the interplanetary dust environment. In order to understand the formation of the dust cloud around airless planetary bodies, it is necessary to deeply understand how ejecta grains are launched from regolith surfaces. We performed new oblique impact experiments on particulate targets to determine the angular and size distributions of ejecta. The spherical Aluminum projectiles of 4 mm were fired by a light gas gun at speeds of around 4.1 km/s. The targets were B4C powders with median diameters of 17 µm and the incident angles were 15°, 30°, and 45° to the target surface. Around the target, arrays of thin Al foils with thicknesses of 15 µm were installed, which were penetrated by high speed ejecta grains. The resulting holes were analyzed with computer vision methods. Our preliminary result is that we found (1) the sizes of major ejecta grains are comparable with median diameters of the target powder; (2) the angular distributions of ejecta varies with the incident angle of the impactor.

Cosmic dust particles are important messengers. They contain information about their origin and their journey through space. The DESTINY+ mission that launches in 2024 provides the opportunity to investigate the dust populations present at 1 AU and around the active asteroid (3200) Phaethon. For this purpose, the Destiny+ Dust Analyzer (DDA) is employed. The instrument is developed under the lead of the University of Stuttgart in Germany. Its capabilities are to simultaneously analyze the dynamical and compositional properties of individual cosmic dust grains that are intersected along the mission. To gain independence from the S/C attitude a two axes pointing mechanism is developed. It provides an azimuthal range of 180° and an elevation range of 90°. The full instrument electronics is developed by the industry partner von Hoerner & Sulger GmbH in Schwetzingen, Germany while the software development takes place at the University of Stuttgart. The mass of the full instrument is ~12 kg and the power consumption is ~35 W in observation mode. The particle trajectory and grain size are determined by the trajectory sensor stage. It utilizes the fact that particles in space carry a surface charge. It consists out of a segmented plane of metal grids of which each is connected to a charge sensitive amplifier. This plane is sandwiched between two grids that are on ground potential. If a charged particle resides in between the grounded planes, it induces a mirror charge on the measurement grid segments. The incident angle, velocity and surface charge of the dust grains are reconstructed from the course and amplitude signal traces. An impact ionization time of flight mass spectrometer provides the compositional analysis of the dust grains. The sensor target is a gold surface with 300 cm² sensitive area and a field of view of 1.99 steradian. Particles collide with the sensor target with relative speeds of several km·s-1. At impact they ionize and the impact plasma is manipulated by electric fields. The cations are accelerated, reflected and focused towards an electron multiplier wich functions as an ion detector. Here the cations are detected with high temporal resolution at two sensitivity stages. This allows to identifie the presence cations in the atomic mass range of 1 – 800 u with a high dynamic range. In the relevant ion mass range of silicates, carbon and metals the mass resolution is high enough so separate the individual atomic species. As the mass spectrometer is highly sensitive to contamination the target can be heater for decontamination. A door cover protects the cleanliness of the sensor interior during launch. Additionaly to the mass spectrum the cation charge is measured by charge sensitive amplifiers at an ion grid in front of the multiplier aperture and an ion ring around it. The negative plasma charge is measured at the target. All signal channels are contiuously active and analyzed by an FPGA. A frame of the signal set is stored as soon as trigger conditions are met. This sensitive yet robust system allows to separate actual dust impacts from noise events. An uncompressed signal set from an individual impact event has a size of ~400 kbit and 2 Gbit non volatile ram is available for storage. Data processing is performed by a SAMRH71 from Microchip. Lossless and lossy compression algorithms are implemented for reducing the packet size for downlink. The talk will give an overview of the instrument functionality and design. We will present the development status and the results of first dust impact measurement will be presented, that are obtained by laboratory measurements with a dust accelerator. Crossection cut through the DDA Sensor. Pointing mechanism and sensor head for measuring cosmic dust particles are depicted. A separate electronics box (not depicted) is located inside the S/C.

Dust Astronomy investigates the nature and the origin of dust particles in space. The particle size distribution ranges from nanodust to approximately 100 micrometer. The study of the elemental and/or chemical composition of the particles together with the knowledge about their origin provides insights into many disciplines. Dust Astronomy is an interdisciplinary working field, which includes Solar System Science, Interstellar Medium studies and Astrobiology. A basic tool for these studies are Dust Telescopes. Dust Telescopes are in-situ instruments to characterize individual dust particles by their velocity vector, size and composition. They are based on impact ionization used for time-of-flight compositional analysis and on charge induction for particle speed and size measurements. In this sense, already the Cassini Cosmic Dust Analyzer (CDA) was a simple Dust Telescope, which successfully characterized the dust environment at Saturn. Now, future missions go even further. In the next years the missions DESTINY+, EUROPA and IMAP will launch. In this talk, a summary is given about the capabilities of Dust Telescopes with a focus on the DESTINY+ Dust Analyser (DDA). DDA is a medium size instrument with a target diameter of 26 cm. A two-axis articulation allows to track dust RAM directions. Larger Telescopes like the record breaking LAMA instrument, developed especially for the measurement of low interstellar dust fluxes, and the instruments for the probes IMAP and EUROPA are compared with DDA. The paper will address questions about the detection of nanodust or, what is a good instrument approach for a Dust Observatory? What are the instrumental challenges for an Interstellar Probe?

Mass spectra from the Cosmic Dust Analyzer (CDA) [1] onboard the Cassini spacecraft revealed the existence of different compositional types of icy dust particles in Saturn’s E-ring. Most of these µm to sub-µm water ice grains were ejected from the cryo-volcanoes at the southern polar region of Enceladus and carry different constituents, for example organic compounds or salts [2-5]. These particles are subject to ongoing plasma sputtering during their lifetime in the E-ring [6,7]. Recent modelling of the dynamics of E-ring particles has shown that, in the region between the orbital distances of Dione and Rhea, the outwards migration of a proportion of the E-ring dust slows down and almost comes to a halt [8]. Due to the minimum of the V-shaped electrostatic grain equilibrium potential [9] and a polarity reversal of the dust surface charges [10], the semi-major axes of the dust particles’ orbits actually stop growing, forcing the particles to spend a significant part of their lifetime at this distance from Saturn. Therefore, this phenomenon should allow plasma sputtering to operate much longer on the dust particles residing in this region, potentially resulting in detectable alterations to the dust particle properties, e.g. particle composition and size, in this region. Here we present the discovery of a new population of grains within the E ring, which show signs of compositional alteration, best explained by plasma sputtering. The radial frequency distribution of these grains shows a distinct accumulation in the region between the orbits of Dione and Rhea, and may provide evidence of prolonged residence there. Analyses of CDA mass spectra of the grains, interpreted via comparison with laboratory Laser‐Induced Liquid Beam Ion Desorption (LILBID) [11] analogue experiments, indicate the particles to be very salt-rich water ice. In comparison to the previously reported salt-rich particle types, generated from Enceladus’ subsurface ocean [3,4] this new population must possess a far higher salt concentration to explain its observed spectral appearance. We propose that the increase in salt concentration arises from sputtering-induced removal of water from less salty oceanic grains (Type 3) [3,4], during their extended time in the region between Dione and Rhea. This population may therefore represent the first confirmation of the proposed dynamical barrier within Saturn’s E-ring. References [1] Srama, R. et al., The Cassini Cosmic Dust Analyzer, Space Science Reviews, 114, 465-518, 2004. [2] Hillier, J. et al., The composition of Saturn’s E ring, Mon. Not. R. Astron. Soc., 377, 1588–1596, 2007 [3] Postberg, F. et al., The E-ring in the vicinity of Enceladus II. Probing the moon’s interior-The composition of E-ring particles, Icarus, 193, 438-454, 2008. [4] Postberg, F. et al., Sodium salts in E-ring ice grains from an ocean below the surface of Enceladus, Nature, 459, 1098-1101, 2009. [5] Postberg, F. et al., A salt-water reservoir as the source of a compositionally stratified plume on Enceladus, Nature, 474, 620–622, 2011 [6] Jurac, S. et al., Saturn’s E Ring and Production of the Neutral Torus, Icarus, 149, 384–396, 2001 [7] Johnson, R. E. et al., Sputtering of ice grains and icy satellites in Saturn’s inner magnetosphere, Planetary and Space Science, 56, 1238–1243, 2008 [8] Kempf & Beckmann, Dynamics and long-term evolution of Saturn's E ring particles (in prep.) [9] Mitchell, C. J. et al., Tenuous ring formation by the capture of interplanetary dust at Saturn, JOURNAL OF GEOPHYSICAL RESEARCH, 110, 2005 [10] Kempf, S. et al., The electrostatic potential of E ring particles, Planetary and Space Science, 54, 999-1006, 2006 [11] Klenner, F. et al., Analogue spectra for impact ionization mass spectra of water ice grains obtained at different impact speeds in space, Rapid Commun Mass Spectrom., 33, 1751–1760, 2019

Rationale Detecting ice grains with impact ionization mass spectrometers in space provides information about the compositions of ice grains and their sources. Depending on the impact speeds of the ice grains onto the metal target of a mass spectrometer, ionization conditions can vary substantially, resulting in changes to the appearance of the resulting mass spectra. Methods Here we accurately reproduce mass spectra of water ice grains, recorded with the Cosmic Dust Analyzer (CDA) on board the Cassini spacecraft at typical impact speeds ranging between 4 km/s to 21 km/s, with a laboratory analogue experiment. In this Laser-Induced Liquid Beam Ion Desorption (LILBID) approach, a μm-sized liquid water beam is irradiated with a pulsed infrared laser, desorbing charged analyte and solvent aggregates and isolated ions, which are subsequently analyzed in a time-of-flight (TOF) mass spectrometer. Results We show that our analogue experiment can reproduce impact ionization mass spectra of ice grains obtained over a wide range of impact speeds, aiding the quantitative analyses of mass spectra from space. Conclusions Spectra libraries created with the LILBID experiment will be a vital tool for inferring the composition of ice grains from mass spectra recorded by both past and future impact ionization mass spectrometers (e.g. the SUrface Dust Analyzer (SUDA) onboard NASA's Europa Clipper Mission or detectors on a future Enceladus Mission).

Airless bodies in the solar system are continually bombarded by meteoroids, sustaining impact ejecta clouds. While large bodies like the Moon retain a significant fraction of ejecta, small asteroids shed this material into the interplanetary dust complex. Measurements of the lunar impact ejecta cloud found it was sustained by the known sporadic meteoroid sources. Here, we extend those measurements using a model of the IDP environment at 1 au to investigate the structure of an ejecta cloud at an eccentric airless body, asteroid 3200 Phaethon. Due to Phaethon's large eccentricity, its ejecta cloud is highly asymmetric. At 1 au, the cloud is canted towards the asteroid's apex direction and its density varies by five orders of magnitude. Compared to a body in a circular orbit at 1 au, Phaethon's peak ejecta density at 1 au is approximately 30 times higher, largely due to enhanced ejecta production from meteoroids shed from Jupiter Family Comets. Such asymmetric ejecta production suggests Phaethon experiences significantly different meteoroid-specific space weathering processes than a body with a similar semi-major axis on a circular orbit. We estimate impact ejecta processes at Phaethon shed approximately 1 ton per year, which is not sufficient to appreciably contribute to the Geminids meteoroid complex. These estimates most likely represent a lower limit, as Phaethon is expected to have a higher ejecta yield than the Moon. Additionally, we calculate predicted impact counts for a dust detector on close flybys of Phaethon in preparation for the DESTINY+ mission and find the large majority of impacts would be detected on the morning-side sunlit hemisphere. These results suggest eccentric asteroids shed more material than those on near-circular orbits, and are suitable candidates for in-situ dust detection and chemical characterization due to their amplified asymmetric ejecta production.

International audience; Planetary rings are a multifaceted player in the system. Recent advances about Saturn’s rings argue that ring science at the ice giants, with magnetospheric and atmospheric sciences, are essential in advancing our knowledge about solar system evolution, the evolution of the moons and Ocean Worlds, and phenomena observed in the ice giant systems.

The Cosmic Dust Analyzer (CDA) onboard Cassini characterized successfully the dust environment at Saturn from 2004 to 2017. Besides the study of Saturn’s E ring and its interaction with the embedded moons, CDA detected nanoparticles in the outer Saturn system moving on unbound orbits and originating primarily from Saturn’s E-ring. Although the instrument was built to detect micron and sub-micron sized particles, nano-sized grains were detected during the flyby at early Jupiter and in the outer environment at Saturn. Fast dust particles with sizes below 10 nm were measured by in-situ impact ionization and mass spectra were recorded. What are the limits of in-situ hypervelocity impact detection and what can be expected with current high-resolution mass spectrometers as flown onboard the missions DESTINY+ or EUROPA? Is the sensitivity of Dust Telescopes sufficient to detect nano-diamonds in interstellar space? This presentation summarizes the current experience of in-situ dust detectors and gives a prediction for future missions. In summary, current Dust Telescopes with integrated high-resolution mass spectrometers are more sensitive than the CASSINI Cosmic Dust Analyzer.

第21回宇宙科学シンポジウム (2021年1月6日-7日. オンライン開催), 21st Space Science Symposium (January 6-7, 2021. Online Meeting), 著者人数: 12名, 資料番号: SA6000163093, レポート番号: g10-9

An in-situ cosmic-dust instrument called the Mercury Dust Monitor (MDM) had been developed as a part of the science payload for the Mio (Mercury Magnetospheric Orbiter, MMO) stage of the joint European Space Agency (ESA)–JAXA Mercury-exploration mission. The BepiColombo spacecraft was successfully launched by an Ariane 5 rocket on October 20, 2018, and commissioning tests of the science payload were successfully completed in near-earth orbit before injection into a long journey to Mercury. MDM has a sensor consisting of four plates of piezoelectric lead zirconate titanate (PZT), which converts the mechanical stress (or strain) induced by dust-particle impacts into electrical signals. After the commencement of scientific operations, MDM will measure the impact momentum at which dust particles in orbit around the Sun collide with the sensor and record the arrival direction. This paper provides basic information concerning the MDM instrument and its predicted scientific operation as a future reference for scientific articles concerning the MDM’s observational data.

The Destiny+ mission (Demonstration and Experiment of Space Technology for Interplanetary voyage Phaethon fLyby and dUst Science) has been selected as part of its M-class Space Science Program by the Japanese space agency JAXA/ISAS and is set to launch in 2023/2024. The mission target is the active asteroid (3200) Phaethon with a projected flyby in early 2028. The scientific payload consists of two cameras (the Telescopic Camera for Phaethon, TCAP, and the Multi-band Camera for Phaethon, MCAP), and the Destiny+ Dust Analyzer (DDA). DDA is the technological successor to the Cosmic Dust Analyzer (CDA) aboard Cassini-Huygens, which prominently investigated the dust environment of the Saturnian system. The DDA sensor is designed as a combination of impact ionization time-of-flight mass spectrometer and trajectory sensor, which will allow for the analysis of sub-micron and micron sized dust particles with respect to their composition (mass resolution m/Δm ≈ 100-150), mass, electrical charge, velocity (about 10% accuracy), and impact direction (about 10° accuracy). Besides attempting to sample the impact-generated dust cloud around Phaethon during the flyby, DDA will be actively observing the interplanetary & interstellar dust environment over the roughly four years spanning cruise phase from the Earth-Moon system through interplanetary space. After launch into a GTO-like orbit, Destiny+ will first employ its solar-electric propulsion system to spiral up to the lunar orbit within about 18 months, followed by a series of lunar swingbys and interim coasting phases in distant cislunar space, accumulating momentum to leave the Earth-Moon system at high excess velocity. The subsequent roughly 2-year interplanetary transfer to intercept Phaethon will be characterized by moderate orbital eccentricity of up to 0.1 and largely unpowered coasting phases. During these four years, the DDA sensor will benefit from a maximum pointing coverage range enabled by its dual-axis pointing mechanism and spacecraft attitude flexibility (during times of unpowered flight). This will allow for exhaustive mapping and analysis of the different interplanetary dust populations, as well as interstellar dust encountered in the region between 0.9-1.1 AU. Here, we give a progress report on the science planning efforts for the 4-year transfer phase. We present a tentative observation timeline that assigns scientific campaigns to different phases of the mission, taking into account results of various dust models, as well as operational and technical constraints.

Due to the their ubiquity and the high impact energy leading to extremely high temperatures and pressures in the affected materials, the physical processes caused by HVIs play an important role in a variety of fields such as the investigation of matter at extreme pressures and temperature, shock waves in solid bodies or even Solar System research, planetology, cosmic dust research and space engineering: Cratering phenomena throughout the Solar System :The first systematic investigation of HVIs of micro-meteoroites was dedicated to the understanding of micro-cratering on lunar rock samples. The size and morphology of resulting micro-craters was investigated as a function of particle size and impact speed. Planetology – Characterization, development and calibration of dust sensors measuring the composition, size and trajectory information of micrometeoroids aboard interplanetary spacecrafts. Astrobiology – Simulation of hyper-velocity impacts of organic micron-sized projectiles and mass spectrometric analysis of impact plasmas containing complex organic molecules; simulation of micrometeoroid impacts onto water ice surfaces. Space weathering: Alteration of bombarded surfaces Cosmic Dust research: A major part of what we know today of HVIs of micro-meteoroites was obtained in the process of developing, calibrating and operation of in situ instruments for the investigation of dust in the Solar System. Thereby induced physical processes generate measurable signals which are then transmitted to Earth and can be analyzed afterwards.There are a variety of methods for in situ dust measurements such as the detection of thin foil penetration, the particle charge, the emerging impact flash or ions generated upon impact, revealing the particles’ velocity, trajectory, mass and even chemical composition. Of all these methods, the generation of charge during impacts provides one of the most sensitive methods for the detection and and the most comprehensible characterization of dust particles in space. The characterization of the dynamical and even chemical properties of dust particles in the Solar System allows us to investigate the origin of cosmic dust and its role in the formation of the Solar System and even its role in the origin of life. Impact physics/Materials under extreme conditions – Investigation of plasma and material conditions of projectile-surface interactions under hyper-velocity impact conditions. Electrostatic dust accelerators To calibrate in-situ dust instruments and to get a deeper understanding of the processes involved, hypervelocity impact measurements under similar and well defined conditions are required. For this purpose, a Van-de-Graaff type ion accelerator was modified at the MPI-K/HD in the late 1960ies. The accelerator was equipped with a dust source capable of charging and accelerating dust particles (Fig. 1). The accelerator covers a large portion of the speed and size ranges needed for most cosmic applications with velocities between 1 to about 80 km s−1 (Fig. 2). After being located for over 5 decades at the MPI-K, the dust accelerator has been moved to the IRS/UniS. This relocation gives us the opportunity to optimize the set up and the also the whole dust research laboratory in its entirety. Particle properties and beam monitoring The dust beam originates from the dust source within the high voltage terminal of the accelerator.(Fig.1). After exiting the source, the dust particles are accelerated in the electrostatic field towards the experimental set-up. Before reaching the experiment chamber, the particles are registered, characterized, and eventually selected while passing the beam line detectors of the Particle Selection Unit (PSU). For this, the particles are been detected by a chain of detectors measuring the particle's primary surface charge using an induction tube and a charge-sensitive amplifier (CSA). The PSU determines the grain speed and mass in order to select individual dust grains on the basis of a speed and mass window given by the experimentator. Cosmological relevant materials Dust Materials: For the above described method of acceleration to work, the particles must therefore be capable of carrying charge and hence the range of materials used has been restricted to those which are either wholly conductive or those with a conductive coating. In the last few years two techniques of coating underwent significant improvements, opening up a whole new range of material types to investigate. Target Materials: Due to the bean geometry and the vacuum conditions , there are a variety of constraints fr the target mounting and properties. Solid metal and silicate target, of terrestrial and meteoritic origin, can be easily used and have been investigated numerous times in the past. Experiments with icy targets are planned for the near future. Investigation of impact ionization with A linear TOF mass spectrometer The characteristics of the impact plasma, such as the velocity distribution of the ions and the ion appearance in the mass spectra, can be analyzed with a linear TOF mass spectrometer. Here, the combination of velocity and angular distributions of the ions results in a broadening of the mass lines, determining their shapes. To study the distribution of the ion velocities alone, we developed an optimized narrow aperture mass spectrometer (Fig.3). The simple set up and the almost homogenous fields allow to calculate the flight times due to the known response function of the instrument. The measured mass line profile can be inverted for the distribution of initial velocity and subsequently the initial kinetic energies of the ions as shown in Fig.4. In addition to TOF other important measurements will address: cratering, secondary ejecta, neutral production, optical spectroscopy of the of the impact flash, and the characterization of the EM waves.The combination of future theoretical studies of the impact processes and the subsequent expansion of the impact produce plasma with this expanded set of measurements will be a powerful tool to investigate the state of the hot compressed matter.

The Cosmic Dust Analyzer (CDA) onboard Cassini characterized successfully the dust environment at Saturn from 2004 to 2017. The study of Saturn’s E ring and its interaction with the embedded moons was a major scientific goal of Cassini. After the end of the mission, the entire CDA data can be analyzed to derive the global parameters of Saturn’s E ring. The CDA instrument measured the primary charge, speed, mass and composition of individual submicron and micron sized dust grains. The instrument was continuously collecting data of dust fluxes and apparent dust densities. Therefore the data cover radial distances between 3 and 20 Saturn radii and equatorial as well as high latitudes. However, the relative impact velocities varied with the dynamical properties of the Cassini spacecraft and with the dust particles. Small relative impact speeds lead to higher mass thresholds for impact detection such that this effect has to be considered in calculating apparent dust densities. Furthermore, the pointing profile of the instrument and the related observation geometry was highly variable. This paper describes an approach to define a dust environment model at Saturn based on the entire CDA dataset.

Full list of authors: Blanc, Michel; Prieto-Ballesteros, Olga; André, Nicolas; Gomez-Elvira, Javier; Jones, Geraint; Sterken, Veerle; Desprats, William; Gurvits, Leonid I.; Khurana, Krishan; Balmino, Georges; Blöcker, Aljona; Broquet, Renaud; Bunce, Emma; Cavel, Cyril; Choblet, Gaël; Colins, Geoffrey; Coradini, Marcello; Cooper, John; Dirkx, Dominic; Fontaine, Dominique; Garnier, Philippe; Gaudin, David; Hartogh, Paul; Hussmann, Hauke; Genova, Antonio; Iess, Luciano; Jäggi, Adrian; Kempf, Sascha; Krupp, Norbert; Lara, Luisa; Lasue, Jérémie; Lainey, Valéry; Leblanc, François; Lebreton, Jean-Pierre; Longobardo, Andrea; Lorenz, Ralph; Martins, Philippe; Martins, Zita; Marty, Jean-Charles; Masters, Adam; Mimoun, David; Palumba, Ernesto; Parro, Victor; Regnier, Pascal; Saur, Joachim; Schutte, Adriaan; Sittler, Edward C.; Spohn, Tilman; Srama, Ralf; Stephan, Katrin; Szegő, Károly; Tosi, Federico; Vance, Steve; Wagner, Roland; Van Hoolst, Tim; Volwerk, Martin; Wahlund, Jan-Erik; Westall, Frances; Wurz, Peter, Europa is the closest and probably the most promising target to search for extant life in the Solar System, based on complementary evidence that it may fulfil the key criteria for habitability: the Galileo discovery of a sub-surface ocean; the many indications that the ice shell is active and may be partly permeable to transfer of chemical species, biomolecules and elementary forms of life; the identification of candidate thermal and chemical energy sources necessary to drive a metabolic activity near the ocean floor. In this article we are proposing that ESA collaborates with NASA to design and fly jointly an ambitious and exciting planetary mission, which we call the Joint Europa Mission (JEM), to reach two objectives: perform a full characterization of Europa's habitability with the capabilities of a Europa orbiter, and search for bio-signatures in the environment of Europa (surface, subsurface and exosphere) by the combination of an orbiter and a lander. JEM can build on the advanced understanding of this system which the missions preceding JEM will provide: Juno, JUICE and Europa Clipper, and on the Europa lander concept currently designed by NASA (Maize, report to OPAG, 2019). We propose the following overarching goals for our Joint Europa Mission (JEM): Understand Europa as a complex system responding to Jupiter system forcing, characterize the habitability of its potential biosphere, and search for life at its surface and in its sub-surface and exosphere. We address these goals by a combination of five Priority Scientific Objectives, each with focused measurement objectives providing detailed constraints on the science payloads and on the platforms used by the mission. The JEM observation strategy will combine three types of scientific measurement sequences: measurements on a high-latitude, low-altitude Europan orbit; in-situ measurements to be performed at the surface, using a soft lander; and measurements during the final descent to Europa's surface. The implementation of these three observation sequences will rest on the combination of two science platforms: a soft lander to perform all scientific measurements at the surface and sub-surface at a selected landing site, and an orbiter to perform the orbital survey and descent sequences. We describe a science payload for the lander and orbiter that will meet our science objectives. We propose an innovative distribution of roles for NASA and ESA; while NASA would provide an SLS launcher, the lander stack and most of the mission operations, ESA would provide the carrier-orbiter-relay platform and a stand-alone astrobiology module for the characterization of life at Europa's surface: the Astrobiology Wet Laboratory (AWL). Following this approach, JEM will be a major exciting joint venture to the outer Solar System of NASA and ESA, working together toward one of the most exciting scientific endeavours of the 21st century: to search for life beyond our own planet. © 2020, The authors received support from the sponsors of their home institutions during the development of their projects, particularly at the two institutes leading this effort: at IRAP, Toulouse, MB and NA acknowledge the support of CNRS, University Toulouse III - Paul Sabatier and CNES. At CAB, Madrid, OPB and JGE acknowledge the support of INTA and Spanish MINECO project ESP2014-55811-C2-1-P and ESP2017-89053-C2-1-P and the AEI project MDM-2017-0737 Unidad de Excelencia "Maria de Maeztu". We would also like to extend special thanks to the PASO of CNES for its precious assistance and expertise in the design of the mission scenario.

Our current understanding of the solar system’s micrometeoroid environment relies to a substantial extent on in-situ data acquired by impact ionization dust detectors such as Ulysses’ and Galileo’s DDS or Cassini’s CDA. Such detectors derive the mass and speed of striking dust particles from the properties and evolution of the plasma created upon impact. In particular, empirical evidence suggests that the impact speed is a function of the duration of impact charge delivery onto the target - the so-called plasma rise time. Often, this dependence has been attributed to secondary impacts of target and projectile ejecta. During recent years the capabilities of laboratory impact detectors have been significantly improved. In particular we now have ample evidence that secondary ejecta impacts are not responsible for the rise-time dependence. In fact the plasma rise-time is rather related to the ionization of target contaminants in the vicinity of the impact site. In this talk we present new experimental data obtained with state-of-the-art impact ionization mass spectrometers, which shed new light on what is really going on during a hypervelocity dust impact. We further discuss the implications for the interpretation of dust data obtained with previous generations of impact ionization detectors.

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.

We review the development of dust science from the first ground-based astronomical observations of dust in space to compositional analysis of individual dust particles and their source objects. A multitude of observational techniques is available for the scientific study of space dust: from meteors and interplanetary dust particles collected in the upper atmosphere to dust analyzed in situ or returned to Earth. In situ dust detectors have been developed from simple dust impact detectors determining the dust hazard in Earth orbit to dust telescopes capable of providing compositional analysis and accurate trajectory determination of individual dust particles in space. The concept of Dust Astronomy has been developed, recognizing that dust particles, like photons, carry information from remote sites in space and time. From knowledge of the dust particles' birthplace and their bulk properties, we learn about the remote environment out of which the particles were formed. Dust Observatory missions like Cassini, Stardust, and Rosetta study Saturn's satellites and rings and the dust environments of comet Wild 2 and comet Churyumov-Gerasimenko, respectively. Supplemented by simulations of dusty processes in the laboratory we are beginning to understand the dusty environments in space., 97 pages, 19 figures, 2 Tables, to be published in ISSI book Cosmic Dust from the Laboratory to the Stars, Edited by Rafael Rodrigo, J\"urgen Blum, Hsiang-Wen Hsu, Detlef Koschny, Anny-Chantal Levasseur-Regourd, Jesus Martin-Pintado, Veerle Sterken and Andrew Westphal

The application of impact ionization for the measurement of micrometeoroids in space is a sensitive and established method for particles in the size range between a few nanometers and a few micrometers. For the measurement of micrometeoroid trajectories, the knowledge of the velocity vector and the related impact position is required. A typical impact ionization detector employs a hemispherically shaped conductive metal target, and a hemispherical grid electrode. The impact charge is dependent on the particle mass, particle speed and incident angle. For a collimated particle flux which is parallel to the symmetry axis, the impact direction and its related impact angle relative to the target normal varies with the radial distance from the symmetry axis. It is therefore essential to consider the impact position during calibration of impact ionization detectors. Furthermore, the induced charge signal shape varies with impact position. We perform simulations with the Coulomb software package and we do compare the results with experimental data. An empirical formula is derived to determine the impact location of the particle from the target and grid induction signals.

Saturn’s moon Enceladus harbours a global water ocean¹, which lies under an ice crust and above a rocky core². Through warm cracks in the crust³ a cryo-volcanic plume ejects ice grains and vapour into space⁴–⁷ that contain materials originating from the ocean⁸,⁹. Hydrothermal activity is suspected to occur deep inside the porous core¹⁰–¹², powered by tidal dissipation¹³. So far, only simple organic compounds with molecular masses mostly below 50 atomic mass units have been observed in plume material⁶,¹⁴,¹⁵. Here we report observations of emitted ice grains containing concentrated and complex macromolecular organic material with molecular masses above 200 atomic mass units. The data constrain the macromolecular structure of organics detected in the ice grains and suggest the presence of a thin organic-rich film on top of the oceanic water table, where organic nucleation cores generated by the bursting of bubbles allow the probing of Enceladus’ organic inventory in enhanced concentrations.

During the Ring Grazing orbits near the end of Cassini mission, the spacecraft crossed the equatorial plane near the orbit of Janus/Epimetheus (similar to 2.5 Rs). This region is populated with dust particles that can be detected by the Radio and Plasma Wave Science (RPWS) instrument via an electric field antenna signal. Analysis of the voltage waveforms recorded on the RPWS antennas provides estimations of the density and size distribution of the dust particles. Measured RPWS profiles, fitted with Lorentzian functions, are shown to be mostly consistent with the Cosmic Dust Analyzer, the dedicated dust instrument on board Cassini. The thickness of the dusty ring varies between 600 and 1,000 km. The peak location shifts north and south within 100 km of the ring plane, likely a function of the precession phase of Janus orbit.

Enceladus is the main source of neutral and charged particles in the Saturnian magnetosphere. The particles originate at more than 100 active geysers forming a plume above the south pole of the moon and are continuously released into Saturn’s magnetosphere. Therefore the understanding of the interaction of those particles and the local magnetospheric environment of the moon is very important. One technique to study that interaction is to study the typical motion of charged particles in the perturbed plasma flow and the associated magnetic field lines in the vicinity of the moon especially during close flybys. The Cassini spacecraft flew by Enceladus 23 times between 2005 and 2015 at distances between 25 and 5000 km. During some of the flybys Cassini went directly through the south polar plume. Other flybys happened north of the moon or on high-latitude trajectories with respect to the moon. In this paper we present the energetic electron measurements during those flybys obtained by the Low Energy Magnetosphere Measurement System LEMMS, part of the Magnetosphere Imaging Instrument MIMI onboard Cassini (Krimigis et al., 2004). As already shown in Krupp et al. (2012) for the first 14 flybys MIMI/LEMMS typically observes dropouts in the particle intensities in the region of disturbed field lines and in the presence of the moon itself or dense material blocking the bounce and drift motions of the particles. We present in this paper a continuation of the Krupp et al. (2012) results and add a full classification for all 23 flybys using the full data set of energetic electron measurements of MIMI/LEMMS. We distinguish the observed absorption and dust signatures into four different categories: (1) full absorption signatures when all the particles within a fluxtube connecting the spacecraft with the moon are lost onto the moon during one of the particle motions; (2) partial dropouts (ramp-like feature) when not all the particles inside the fluxtube are lost; (3) short dropouts in the fluxes when particles are suddenly lost for a short period in time; and interpret those features as full or partial losses onto the moon or its environment as a result of different plasma and dust regimes in the vicinity of Enceladus. We compare the results with those of Meier et al. (2014) and Engelhardt et al. (2015); (4) In addition we also show dust-related “false electron” measurements for those flybys when Cassini directly went through the dense regions of the south polar plume. Those “dust-peaks” can be interpreted as the result of impacting dust particles inside the LEMMS aperture or nearby creating a plasma cloud.

Alkali metal doped fullerides (A3C60) are superconductors with critical temperatures, Tc, extending up to 38 K. Tc is known to depend strongly on the lattice parameter a, which can be adjusted by physical or chemical pressure. In the latter case an alkali atom is replaced by a different sized one, which changes a. We have collected an extensive data base of experimental data for Tc from very early up to recent measurements. We disentangle alkali atom chemical effects on Tc, beyond the well-known consequences of changing a. It is found that Tc, for a fixed a, is typically increased as smaller alkali atoms are replaced by larger ones, except for very large a. Possible reasons for these results are discussed. Although smaller in size than the lattice parameter contribution, the chemical effect is not negligible and should be considered in future physical model developments.

Circumstellar discs are known to exist in great variety, from gas-rich discs around the youngest stars to evolved debris discs such as the solar system’s zodiacal cloud. Through gravitational interaction, exoplanets embedded in these discs can generate density variations, imposing potentially observable structural features on the disc such as rings or gaps. Here we report on a mirrored double crescent pattern arising in simulations of discs harbouring a small, moderately eccentric planet - such as Mars. We show that the structure is a result of a directed apsidal precession occurring in particles that migrate the planet’s orbital region under Poynting-Robertson drag. We further analyze the strength of this effect with respect to planet and particle parameters.

Charged dust particles in space can be detected by in situ sensors using charge induction. Such trajectory sensors are normally based on many grid or wire electrodes connected to individual charge sensitive amplifiers. In this article we describe a new approach to measure the trajectory of a charged dust particle by a single charge sensitive amplifier. The signal shape is used to calculate particle speed, mass and trajectory. The detector employs two half-circular grid electrodes, and the electrodes are connected to the differential input stage of an amplifier. Simulations using the Coulomb 9.0 software package were performed in order to determine the expected signal shapes depending on the particle parameters (entry location and incident angles). The simulated charge signals show, that the chosen measurement concept is an efficient method for low-power and low-mass dust trajectory sensors.

The JAXA/ISAS spacecraft DESTINY$^+$ will be launched to the active asteroid (3200) Phaethon in 2022. Among the proposed core payload is the DESTINY+ Dust Analyzer (DDA) which is an upgrade of the Cosmic Dust Analyzer flown on the Cassini spacecraft to Saturn (Srama et al. 2011). We use two up-to-date computer models, the ESA Interplanetary Meteoroid Engineering Model (IMEM, Dikarev et al. 2005), and the interstellar dust module of the Interplanetary Meteoroid environment for EXploration model (IMEX; Sterken2013 et al., Strub et al. 2019) to study the detection conditions and fluences of interplanetary and interstellar dust with DDA. Our results show that a statistically significant number of interplanetary and interstellar dust particles will be detectable with DDA during the 4-years interplanetary cruise of DESTINY+. The particle impact direction and speed can be used to descriminate between interstellar and interplanetary particles and likely also to distinguish between cometary and asteroidal particles., Comment: 40 pages, 18 Figures, accepted for Planetary and Space Science

Context.The interplanetary dust complex is currently understood to be largely the result of dust production from Jupiter-family comets, with contributions also from longer-period comets (Halley- and Oort-type) and collisionally produced asteroidal dust.Aims.Here we develop a dynamical model of the interplanetary dust cloud from these source populations in order to develop a risk and hazard assessment tool for interplanetary meteoroids in the inner solar system.Methods.The long-duration (1 Myr) integrations of dust grains from Jupiter-family and Halley-type comets and main belt asteroids were used to generate simulated distributions that were compared to COBE infrared data, meteor data, and the diameter distribution of lunar microcraters. This allowed the constraint of various model parameters.Results.We present here the first attempt at generating a model that can simultaneously describe these sets of observations. Extended collisional lifetimes are found to be necessary for larger (radius ≥ 150μm) particles. The observations are best fit with a differential size distribution that is steep (slope = 5) for radii ≥ 150μm, and shallower (slope = 2) for smaller particles. At the Earth the model results in ~ 90–98% Jupiter-family comet meteoroids, and small contributions from asteroidal and Halley-type comet particles. In COBE data we find an approximately 80% contribution from Jupiter-family comet meteoroids and 20% from asteroidal particles. The resulting flux at the Earth is mostly within a factor of about two to three of published measurements.

Cassini's last look at Saturn's rings During the final stages of the Cassini mission, the spacecraft flew between the planet and its rings, providing a new view on this spectacular system (see the Perspective by Ida). Setting the scene, Spilker reviews the numerous discoveries made using Cassini during the 13 years it spent orbiting Saturn. Iess et al. measured the gravitational pull on Cassini, separating the contributions from the planet and the rings. This allowed them to determine the interior structure of Saturn and the mass of its rings. Buratti et al. present observations of five small moons located in and around the rings. The moons each have distinctive shapes and compositions, owing to accretion of ring material. Tiscareno et al. observed the rings directly at close range, finding complex features sculpted by the gravitational interactions between moons and ring particles. Together, these results show that Saturn's rings are substantially younger than the planet itself and constrain models of their origin. Science , this issue p. 1046 , p. eaat2965 , p. eaat2349 , p. eaau1017 ; see also p. 1028

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 table

Saturn’s moon Enceladus is erupting a plume of gas and ice grains from its south pole. Linked directly to the moon’s subsurface global ocean, plume material travels through cracks in the icy crust and is ejected into space. The subsurface ocean is believed to be in contact with the rocky core, with ongoing hydrothermal activity present. The Cassini spacecraft’s Ion and Neutral Mass Spectrometer (INMS) detected volatile, gas phase, organic species in the plume and the Cosmic Dust Analyser (CDA) discovered high-mass, complex organic material in a small fraction of ice grains. Here, we present a broader compositional analysis of CDA mass spectra from organic-bearing ice grains. Through analogue experiments, we find spectral characteristics attributable to low-mass organic compounds in the Enceladean ice grains: nitrogen-bearing, oxygen-bearing, and aromatic. By comparison with INMS results, we identify low-mass amines [particularly (di)methylamine and/or ethylamine] and carbonyls (with acetic acid and/or acetaldehyde most suitable) as the best candidates for the N- and O-bearing compounds, respectively. Inferred organic concentrations in individual ice particles vary but may reach tens of mmol levels. The low-mass nitrogen- and oxygen-bearing compounds are dissolved in the ocean, evaporating efficiently at its surface and entering the ice grains via vapour adsorption. The potentially partially water soluble, low-mass aromatic compounds may alternatively enter ice grains via aerosolization. These amines, carbonyls, and aromatic compounds could be ideal precursors for mineral-catalysed Friedel–Crafts hydrothermal synthesis of biologically relevant organic compounds in the warm depths of Enceladus’ ocean.

Interactions between the solar wind and planetary magnetospheres provide important diagnostic information about the magnetospheric dynamics. The lack of monitoring of upstream solar wind conditions at the outer planets, however, restrains the overall scientific output. Here we apply a new method, using Cassini nanodust stream measurements, to derive the interplanetary magnetic field structure during the 2013 Saturn aurora campaign. Due to the complex dynamical interactions with the interplanetary magnetic field, a fraction of fast nanodust particles emerging from the Saturnian system is sent back into the magnetosphere and can be detected by a spacecraft located within. The time-dependent directionality caused by the variable interplanetary magnetic field enable these particles to probe the solar wind structure remotely. Information about the arrival time of solar wind compression regions (coupled with the heliospheric current sheet crossings) as well as the field direction associated with the solar wind sector structure can be inferred. Here we present a tentative identification of the interplanetary magnetic field sector structure based on Cassini nanodust and radio emission measurements during the 2013 Saturn aurora campaign. Our results show that, the interplanetary magnetic field near Saturn during 2013-080 to 176 was consistent with a two-sector structure. The intensifications of aurora and the radio emission on 2013-095, 112 and 140 coincide with the IMF sector boundaries, indicating that the encounter of the compressed solar wind is the main cause of the observed activities.

The lunar surface is continuously exposed to the micrometeoroid environment. Hypervelocity impacts of interplanetary dust particles with speeds around 17 km s − 1 generate secondary ejecta on the lunar surface. A dust detector placed on the moon is capable of characterizing the secondary ejecta population. The purpose of this paper is to study the speed and trajectory information of ejecta by impact simulations and its implications for the location of a dust sensor on the surface. AUTODYN15.0/2D software was used to simulate the velocity and angular distributions of ejecta created by the primary impacts of interplanetary dust particles. We considered projectiles with sizes of 10 μ m spheres in diameter with speeds of 17 km s − 1 . We used impact angles of 15°, 30°, 45°, 60°, 75°, and 90° with respect to the surface. A significant percentage of the impact ejecta are created in the early-time stage of the impact process. This population can be captured by a sensor placed on the lunar surface (e.g. Lunar Ejecta and Meteorites (LEAM) experiment) or by a sensor mounted directly on a lander (e.g. Lunar Dust eXplorer (LDX)). The secondary ejecta population above the lunar surface is considered to explain the results of the LEAM experiment. A sensor directly placed on the surface like LEAM is not very well suited to measure the high-speed ejecta component – a sensor located at a few meters height (e.g. on top of a lunar lander) would measure higher fluxes.

Cometary meteoroid trails exist in the vicinity of comets, forming fine structure of the interplanetary dust cloud. The trails consist predominantly of cometary particles with sizes of approximately 0.1 mm to 1 cm which are ejected at low speeds and remain very close to the comet orbit for several revolutions around the Sun. When re-analysing the Helios dust data measured in the 1970s, Altobelli et al. (2006) recognized a clustering of seven impacts, detected in a very narrow region of space at a true anomaly angle of 135 deg, which the authors considered as potential cometary trail particles. We re-analyse these candidate cometary trail particles to investigate the possibility that some or all of them indeed originate from cometary trails and we constrain their source comets. The Interplanetary Meteoroid Environment for eXploration (IMEX) dust streams in space model is a new universal model for cometary meteoroid streams in the inner solar system, developed by Soja et al. (2015). Using IMEX we study cometary trail traverses by Helios. During ten revolutions around the Sun, and in the narrow region of space where Helios detected the candidate dust particles, the spacecraft repeatedly traversed the trails of comets 45P/Honda-Mrkos-Pajduvsakova and 72P/Denning-Fujikawa. Based on the detection times and particle impact directions, four detected particles are compatible with an origin from these two comets. We find a dust spatial density in these trails of about 10^-8 to 10^-7 m^-3. The in-situ detection and analysis of meteoroid trail particles which can be traced back to their source bodies by spacecraft-based dust analysers opens a new window to remote compositional analysis of comets and asteroids without the necessity to fly a spacecraft to or even land on those celestial bodies. This provides new science opportunities for future missions like Destiny+, Europa Clipper and IMAP., Comment: 13 pages, 9 Figures, 2 Tables, accepted for pubication by Astronomy and Astrophysics

Plain Language Summary Cassini flew through the gap between Saturn and its rings for 22 times before plunging into the atmosphere of Saturn, ending its 20-year mission. The radio and plasma waves instrument on board Cassini helped quantify the dust hazard in this previously unexplored region. The measured density of large dust particles was much lower than expected, allowing high-value science observations during the subsequent Grand Finale orbits.

INTRODUCTION During the Cassini spacecraft’s Grand Finale mission in 2017, it performed 22 traversals of the 2000-km-wide region between Saturn and its innermost D ring. During these traversals, the onboard cosmic dust analyzer (CDA) sought to collect material released from the main rings. The science goals were to measure the composition of ring material and determine whether it is falling into the planet’s atmosphere. RATIONALE Clues about the origin of Saturn’s massive main rings may lie in their composition. Remote observations have shown that they are formed primarily of water ice, with small amounts of other materials such as silicates, complex organics, and nanophase hematite. Fine-grain ejecta generated by hypervelocity collisions of interplanetary dust particles (IDPs) on the main rings serve as microscopic samples. These grains could be examined in situ by the Cassini spacecraft during its final orbits. Deposition of ring ejecta into Saturn’s atmosphere has been suggested as an explanation for the pattern of ionospheric H 3 + infrared emission, a phenomenon known as ring rain. Dynamical studies have suggested a preferential transport of charged ring particles toward the planet’s southern hemisphere because of the northward offset of Saturn’s internal magnetic field. However, the deposition flux and its form (ions or charged grains) remained unclear. In situ characterization of the ring ejecta by the Cassini CDA was planned to provide observational constraints on the composition of Saturn’s ring system and test the ring rain hypothesis. RESULTS The region within Saturn’s D ring is populated predominantly by grains tens of nanometers in radius. Larger grains (hundreds of nanometers) dominate the mass density but are narrowly confined within a few hundred kilometers around the ring plane. The measured flux profiles vary with the CDA pointing configurations. The highest dust flux was registered during the ring plane crossings when the CDA was sensitive to the prograde dust populations (Kepler ram pointing) (see the figure). When the CDA was pointed toward the retrograde direction (plasma ram pointing), two additional flux enhancements appeared on both sides of the rings at roughly the same magnetic latitude. The south dust peak is stronger and wider, indicating the dominance of Saturn’s magnetic field in the dynamics of charged nanograins. These grains are likely fast ejecta released from the main rings and falling into Saturn, producing the observed ionospheric signature of ring rain. We estimate that a few tons of nanometer-sized ejecta is produced each second across the main rings. Although this constitutes only a small fraction ( CONCLUSION Our observations illustrate the interactions between Saturn and its main rings through charged, nanometer-sized ejecta particles. The dominance of nanograins between Saturn and its rings is a dynamical selection effect, stemming from the grains’ high ejection speeds (hundreds of meters per second and higher) and Saturn’s offset magnetic field. The presence of the main rings modifies the effects of the IDP infall to Saturn’s atmosphere. The rings do this asymmetrically, leading to the distribution of the ring rain phenomenon. Confirmed ring constituents include water ice and silicates, whose ratio is likely shaped by processes associated with ring erosion processes and ring-planet interactions.

The interplanetary space probe Cassini/Huygens reached Saturn in July 2004 after seven years of cruise phase. The Cosmic Dust Analyzer (CDA) measures the interplanetary, interstellar and planetary dust in our solar system since 1999 and provided unique discoveries. In 1999, CDA detected interstellar dust in the inner solar system followed by the detection of electrical charges of interplanetary dust grains during the cruise phase between Earth and Jupiter. The instrument determined the composition of interplanetary dust and the nanometre sized dust streams originating from Jupiter's moon Io. During the approach to Saturn in 2004, similar streams of submicron grains with speeds in the order of 100 km/s were detected from Saturn's inner and outer ring system and are released to the interplanetary magnetic field. Since 2004 CDA measured more than one million dust impacts characterizing the dust environment of Saturn. The instrument is one of three experiments which discovered the active ice geysers located at the south pole of Saturn's moon Enceladus in 2005. Later, a detailed compositional analysis of the water ice grains in Saturn's E ring system lead to the discovery of large reservoirs of liquid water (oceans) below the icy crust of Enceladus. Finally, the determination of the dust- magnetosphere interaction and the discovery of the extended E ring (at least twice as large as predicted) allowed the definition of a dynamical dust model of Saturn's E ring describing the observed properties. This paper summarizes the discoveries of a ten year story of success based on reliable measurements with the most advanced dust detector flown in space until today. This paper focuses on cruise results and findings achieved at Saturn with a focus on flux and density measurements., 18 pages, 12 Figures, DLRK 2011

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 (, Comment: 17 pages, 17 figures

第18回宇宙科学シンポジウム (2018年1月9日-10日. 宇宙航空研究開発機構宇宙科学研究所(JAXA)(ISAS)相模原キャンパス), 相模原市, 神奈川県, 18th Space Science Symposium (January 9-10, 2018. Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency(JAXA)(ISAS)Sagamihara Campus), Sagamihara, Kanagawa Japan, 資料番号: SA6000118135, レポート番号: P-102

A dust trajectory detector placed on the lunar surface is exposed to extend people’s knowledge on the dust environment above the lunar surface. The new design of Lunar Dust eXplorer (LDX) is well suited for lunar or asteroid landers with a broad range of particle charges (0.1–10 fC), speeds (few m s−1 to few km s−1) and sizes (0.1–10 μ m). The calibration of dust trajectory detector is important for the detector development. We do present experimental results to characterize the accuracy of the newly developed LDX laboratory model. Micron sized iron particles were accelerated to speed between 0.5 and 20 km s−1 with primary charges larger than 1 fC. The achieved accuracies of the detector are ± 5 % and ± 7 % for particle charge and speed, respectively. Dust trajectories can be determined with measurement accuracy better than ± 2°. A dust sensor of this type is suited for the exploration of the surface of small bodies without an atmosphere like the Earth’s moon or asteroids in future, and the minisatellites are also suitable carriers for the study of interplanetary dust and manned debris on low Earth orbits.