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The Interstellar Mapping and Acceleration Probe (IMAP) is scheduled to launch in 2025, to be stationed at the Sun-Earth L1 Lagrange point with a combination of 10 in-situ and remote sensing instruments. A primary science goal of IMAP is to improve our understanding of the composition and properties of the local interstellar medium. The local interstellar medium contains plasma, magnetic fields, neutral atoms, cosmic rays, and dust which all influence the heliosphere through interconnected time-dependent and multi-scale processes. The Interstellar Dust Experiment (IDEX) instrument onboard IMAP will measure the flux, size distribution, and composition of interstellar dust particles (ISD), characterizing the inflowing solid matter from the local interstellar medium reaching the inner heliosphere. IDEX will determine whether the composition of the contemporary local interstellar cloud's dust population is consistent with being the feedstock for the formation of the Solar System. In addition to heliospheric science goals, IDEX will also detect the shared pool of interplanetary dust particles (IDP) of cometary and asteroidal origin and determine whether some IDPs preserve unprocessed pre-solar molecular cloud particles or show signatures of processing in the solar system. IDEX will identify primary organic material from asteroids and various cometary families to determine if they share a common source or are formed from distinct reservoirs. IDEX dust detection is based on impact ionization, where elemental and molecular ions are generated in a high-velocity dust impact and analyzed in a time-of-flight (TOF) setup. This talk will discuss the expected scientific results of IDEX that are of primary importance to heliospheric, astrophysical, and planetary sciences. This talk will summarize our current understanding of the ISD and IDP inventory and the expected improvements by the IMAP mission.

Our solar system has evolved through accretion of dust and gas as the Sun and its protective magnetic bubble – “the heliosphere” - have plowed through interstellar space on its journey through the galaxy. Over the course of its evolution, the solar system has encountered dramatically different interstellar properties resulting in a severely compressed heliosphere with periods of full exposures of interstellar gas, plasma, dust and galactic cosmic rays (GCRs) that all have helped shaped the system we live in today. Our current knowledge lacks the direct measurements necessary to understand how our star upholds its vast heliosphere and its potentially game-changing role in the evolution of our galactic home.Voyager 1 and 2 are now in the Very Local Interstellar Medium (VLISM), where they are expected to operate until the mid-2030’s having uncovered many unexpected discoveries and mysteries. After its paradigm-shifting discoveries at Pluto and Arrokoth, New Horizons is currently the only spacecraft in the outer heliosphere and is following the same heliospheric longitude as Voyager 2, but in the ecliptic plane – a trajectory that intersects the IBEX ribbon. It is projected to operate across the heliospheric termination shock and possible the heliopause with new measurements that will shed light on many of the mysteries of our heliosphere. Now passing 55 au, New Horizons is uniquely positioned to investigate the evolution of the solar wind, energetic particles, GCRs, and, in particular interstellar Pick-Up Ions (PUIs) that Voyager was not equipped to measure, to help constrain the structure and dynamics of the heliosphere. Observations of GCRs offers an opportunity to understand how these scatter strongly in the wavy structure of the “ballerina skirt” of the solar magnetic field leading to the strong modulation as part of the overall heliospheric shielding.As New Horizons continues to travel outward, dust measurements may reveal an interstellar component that will provide the strongest constraint to date on how interstellar dust grains interact with the heliosphere. Now beyond the infrared and UV haze of the circumsolar dust and hydrogen gas, the Alice UV camera holds promise to search for signatures of the hydrogen wall and perhaps even signatures of our neighboring interstellar clouds.New Horizons continues to break new ground in understanding the formation of our solar system by revealing the properties of multiple distant Kuiper Belt Objects and provide critical constraints on the structure of the Sun’s enormous dust disk. Because of its distant position, New Horizons is also providing the unprecedented estimates of the cosmic background.In this presentation we provide an overview of New Horizons’ heliophysics observations in the context of the exploration by Voyager, IBEX, and IMAP. We conclude by providing a status of the future Interstellar Probe mission concept that is now under consideration in the Solar and Space Physics Decadal Survey.

Space missions often carry antenna instruments that are sensitive to dust impacts, however, the understanding of signal generation mechanisms remained incomplete. A signal generation model in an analytical form is presented that provides a good agreement with laboratory measurements. The model is based on the direct and induced charging of the spacecraft from the collected and escaping fraction of free charges from the impact-generated plasma cloud. A set of laboratory experiments is performed using a 20:1 scaled-down model of the Cassini spacecraft in a dust accelerator facility. The results show that impact plasmas can be modeled as a plume of ions streaming away from the impact location and a cloud of isotropically expanding electrons. The fitting of the model to the collected antenna waveforms provides some of the key parameters of the impact plasma. The model also shows that the amplitudes of the impact signals can be significantly reduced in typical space environments due to the discharging effects in the ambient plasma., Comment: Manuscript accepted online by JGR: Space Physics on 05 April 2021

Dust hazards are considered to be one of the technical challenges for future lunar exploration. In our past work a new dust mitigation technology was introduced utilizing an electron beam to remove dust particles from various surfaces. This technology was developed based on a patched charge model, which shows that the emission and re-absorption of electron beam induced secondary electrons inside microcavities between dust particles can lead to sufficiently large charges on the dust particles, causing their release from the surface due to strong repulsive forces. In this paper an improvement in the effectiveness of this technology is demonstrated with varying the beam incident angle on dust-covered sample surfaces by rotating the samples relative to the beam. Due to random arrangements of the microcavities, more of them will be exposed to the beam with various incident angles, thereby causing more dust release from the surface. The cleaning performance is tested against three samples: glass, spacesuit, and a photovoltaic (PV) panel. Lunar simulant (

The Lunar Laser Ranging Retro-reflectors (LRR) allow for the precise measurement of the travel time of laser pulses from the Earth to the lunar surface and back. Dust accumulation on the LRRs scatters the reflected light used for laser interferometry measurements leading to a reduction in the return signal amplitude by a factor of ≃ 10. We report on a series of experiments utilizing a method of an iterative application and removal of an acrylic adhesive kapton tape to remove lunar dust simulant from a glass substrate. The effectiveness of adhesive tape was determined by measuring the transmission of an expanded laser beam through a glass substrate with a dusted surface. Calibration data was obtained before the glass was exposed to any dust, and light transmission was measured after each iteration of adhesive removal using a power meter. The procedure was repeated using heavy gloves while keeping the glass substrate at 120 ° C to simulate the temperature conditions of a lunar day on the surface. A third test was conducted at room temperature in high-vacuum to ensure functionality in the lunar environment. These experiments show that glass substrates can be restored to 98 ± 2 % of their original transmission using the adhesive tape method. Therefore the light that travels into and out of the quartz surface of the LLRs can be restored up to 96 ± 4 % of their initial transmission.

Dust mobilized on the lunar surface due to natural processes and/or human activities can readily stick to spacesuits, optical devices, and mechanical components, for example. This may lead to dust hazards that have been considered as one of the technical challenges for future lunar exploration. Several dust mitigation technologies have been investigated over the past years. Here we present a new method utilizing an electron beam to shed dust off of surfaces. Recent studies on electrostatic dust lofting have shown that the emission and absorption of secondary electrons or photoelectrons inside microcavities forming between dust particles can cause the buildup of substantial negative charges on the surrounding particles. The subsequent repulsive forces between these particles can cause their release from the surface. Fine-sized lunar simulant particles (JSC-1A

Plasma Wave antenna instruments are employed on a range of space missions and can also be used to characterize the population of cosmic dust particles. Such measurements are complementary to those made by a dedicated dust instrument and suitable for the detection of larger (> 1 micron) particles. These booms or deployed wires with receiving elements are sensitive to the plasma cloud generated by the hypervelocity impact of a dust particle on the spacecraft, or the antenna itself. The dust impact is registered as a transient voltage signal (waveform) that is due to the charging of the spacecraft/antenna, and the induced charging from the part of the plasma cloud that is expanding from the impact location. Recent advancements provide the capability of obtaining the mass of the impacting particle from the measured waveforms. The new models are based on first principles and account for the parameters of the impact plasma (in terms of effective temperatures and the geometry of the expansion), the parameters of the ambient space environment, and the geometry of the spacecraft. The latter two allow for determining the approximate impact location on the spacecraft and thus constrain the incoming direction of the dust particle. Once the expansion of the transient impact plasma is over, the spacecraft and the antennas discharge through the ambient environment and relax back to their equilibrium potentials. The analysis of the measured waveforms thus also provides information on the density of the ambient plasma and its temperature. The numerical model is applied for the reanalysis of the measurements made by the STEREO spacecraft.

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?

Pluto energies of a few kiloelectron volts and suprathermal ions with tens of kiloelectron volts and above. We measure this population using the Pluto Energetic Particle Spectrometer Science Investigation (PEPSSI) instrument on board the New Horizons spacecraft that flew by Pluto in 2015. Even though the measured ions have gyroradii larger than the size of Pluto and the cross section of its magnetosphere, we find that the boundary of the magnetosphere is depleting the energetic ion intensities by about an order of magnitude close to Pluto. The intensity is increasing exponentially with distance to Pluto and reaches nominal levels of the interplanetary medium at about 190

Given the compositional diversity of asteroids, and their distribution in space, it is impossible to consider returning samples from each one to establish their origin. However, the velocity and molecular composition of primary minerals, hydrated silicates, and organic materials can be determined by in situ dust detector instruments. Such instruments could sample the cloud of micrometer-scale particles shed by asteroids to provide direct links to known meteorite groups without returning the samples to terrestrial laboratories. We extend models of the measured lunar dust cloud from LADEE to show that the abundance of detectable impact-generated microsamples around asteroids is a function of the parent body radius, heliocentric distance, flyby distance, and speed. We use monte carlo modeling to show that several tens to hundreds of particles, if randomly ejected and detected during a flyby, would be a sufficient number to classify the parent body as an ordinary chondrite, basaltic achondrite, or other class of meteorite. Encountering and measuring microsamples shed from near-earth and main-belt asteroids, coupled with complementary imaging and multispectral measurements, could accomplish a thorough characterization of small, airless bodies., 19 pages, 3 Tables, 10 Figures, accepted May 30, 2019

The Student Dust Counter (SDC) is an in-situ dust detector aboard the New Horizons spacecraft observing the distribution of interplanetary dust particles (IDPs) with mass > 10 − 12 g or approximately 0.5 µm in radius. New Horizons was launched on January 19th, 2006 and performed a fly-by of the Pluto system on July 14th, 2015. SDC has nearly continuously mapped the dust density distribution along the trajectory of New Horizons, and it continues to operate providing measurements of the IDP in the Edgeworth–Kuiper Belt (EKB). We present results of the dust density distribution from 1 to 38 AU and compare these measurements to existing theoretical models.

Glow discharges are produced in air in a ~1-m-long glass vacuum tube under the pressure of 12-113 mtorr. We present the full potential profiles throughout the glow discharge regions characterized using a cold emissive probe with the current-bias method. Secondary electron emission from the probe likely determines the local plasma potential, which replaces the role of thermionic emission that fails in relatively high-pressure plasmas. The measured potential profiles show good agreement with the theoretical expectations. A large potential drop is measured in the cathode dark space followed by a potential plateau through the negative glow and Faraday dark space regions. Striations in the positive column are shown as stair-step-like multiple potential double layers with a potential step close to the ionization energy. This cold emissive probe method can be used for characterizing potentials in even higher pressure (>1 torr) glow discharges that are not yet well understood.

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; The dynamics of lofted dust on airless bodies have been the subject of much study since the 1960s, when the lunar horizon glow was first observed. Lofted dust dynamics have important implications for the evolution of an airless body's surface properties. To date, most of these studies have had to rely on assumptions of initial conditions of the lofted dust grains due to a lack of experimental results. In this paper, we present a study of lofted dust grains, making use of initial conditions obtained from recent laboratory results. Additionally, we distinguish between photoemission rates from isolated dust grains and from the bulk regolith. We explore dust lofting dynamics across a large size range of dust grains (0.1 to 10 μm) and the surface gravity of their parent bodies (0.0001 to 1 lunar g). Charging and lofting results reveal a complex interplay between the grain size, gravity, initial charge, and the various charging currents. It is shown that the sheath electric field becomes increasingly significant in the lofted dust dynamics as the gravitational field decreases. Due to the initial negative charge of dust grains lofted from a positively charged regolith surface, their lofting heights are found to be generally reduced compared to uncharged grains with similar initial speeds. We show that micron-sized dust grains can be lofted to high altitudes and even escape from smaller bodies, leading to the loss of fine-grained materials from the surface.

International audience; Interplanetary dust is a scientifically important constituent of the Solar System that consists of material shed by asteroids, comets, and other airless bodies. As used here, the term “dust” includes interplanetary dust particles and micrometeoroids. Dust has been studied by missions such as Mariner, Pioneer, and Voyager in both interplanetary space and in the vicinity of most of the planets.To date, however, no dedicated interplanetary dust instrument has yet been employed for detailed analysis of the dust environment of Mars. Partial data on dust flux has been provided by the 1965 Mariner IV flyby, the MAVEN orbiter, and other missions, but a complete understanding of interplanetary dust abundance, composition, debris hazard, annual flux variation, and origins is lacking. These data are critical for understanding the effects of dust upon the martian system, including the carbonaceous input into the regolith of Mars and its moons, the chemical input into the martian atmosphere, potential effects upon remote sensing data, the hypothesized existence of a Phobos dust ring, and possible annual variations from meteor shower infall. These effects have direct ramifications for interpretation of Mars/Phobos/Deimos mission science and analysis of returned samples from those worlds. To remediate this shortfall, the authors recommend that a dedicated interplanetary dust analysis instrument should be included in the instrument package for an upcoming martian orbiter in the near term. Such an interplanetary dust analysis instrument should collect data over a time period of several martian years in order to generate a statistically robust data set on interplanetary dust concentration and flux over a wide range of mass, and to discern temporal variation over multiple martian years.

International audience

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.

We discuss in a thermodynamic, geologically empirical way the long-term nature of the stable majority ices that could be present in Kuiper Belt Object 2014 MU69 after its 4.6 Gyr residence in the EKB as a cold classical object. Considering the stability versus sublimation into vacuum for the suite of ices commonly found on comets, Centaurs, and KBOs at the average ~40K sunlit surface temperature of MU69 over Myr to Gyr, we find only 3 common ices that are truly refractory: HCN, CH3OH, and H2O (in order of increasing stability). NH3 and H2CO ices are marginally stable and may be removed by any positive temperature excursions in the EKB, as produced every 1e8 - 1e9 yrs by nearby supernovae and passing O/B stars. To date the NH team has reported the presence of abundant CH3OH and evidence for H2O on MU69s surface (Lisse et al. 2017, Grundy et al. 2020). NH3 has been searched for, but not found. We predict that future absorption feature detections will be due to an HCN or poly-H2CO based species. Consideration of the conditions present in the EKB region during the formation era of MU69 lead us to infer that it formed "in the dark", in an optically thick mid-plane, unable to see the nascent, variable, highly luminous Young Stellar Object-TTauri Sun, and that KBOs contain HCN and CH3OH ice phases in addition to the H2O ice phases found in their Short Period comet descendants. Finally, when we apply our ice thermal stability analysis to bodies/populations related to MU69, we find that methanol ice may be ubiquitous in the outer solar system; that if Pluto is not a fully differentiated body, then it must have gained its hypervolatile ices from proto-planetary disk sources in the first few Myr of the solar systems existence; and that hypervolatile rich, highly primordial comet C/2016 R2 was placed onto an Oort Cloud orbit on a similar timescale., Comment: 34 Pages, 5 Figures, 2 SOM Tables

Charge sensitive amplifiers (CSAs) are electronic integrating circuits frequently used for detecting quick charge pulses such as those produced in semiconductor detector devices and electron multipliers. One of the limitations of highly sensitive CSA circuits is the accuracy with which they can be calibrated due to the necessity of using injection capacitors on the order of a few pF, which are difficult to calibrate and to disentangle from other stray capacitance in calibration circuits. This paper presents an alternate method for calibrating the electronics for CSAs with conductive detectors, referred to as the "external conductor" method, using the detector itself to form the injection circuit. The external conductor method is compared to the traditional injection capacitor method for an example detector. The new method results in an increase to the calibration factor of up to 70% over the value derived from a traditional injection capacitor, with an uncertainty in the new value of 2%. Finally, the results from the external conductor method are compared to a third, independent approach, which uses reference charged particles as calibration sources in the Colorado dust accelerator. The results of the charged particle approach corroborate the external conductor calibration to within the stated uncertainty.

The Lunar Environment Monitoring Station (LEMS) is an instrument concept funded by NASA’s Development of Advanced Lunar Instrumentation (DALI) Program, and undergoing maturation at NASA's Goddard Space Flight Center. LEMS has been proposed to the NASA's recent call for Payloads and Research Investigations on the Surface of the Moon (PRISM).LEMS is a compact, autonomous, self-sustaining and long-lasting instrument suite that enables in situ, continuous, long-term monitoring of the lunar exosphere and of the most relevant natural and manmade controlling processes (infall of interplanetary dust particles (IDP), influx of solar wind and magnetospheric particles, EUV irradiation, interior outgassing, disturbances by landers and human surface activities). LEMS can be delivered to the surface of the Moon by crewed or robotic missions. Once deployed (on a deck or directly on the surface), LEMS will operate day and night for a nominal duration of 2 years without requiring any additional support or resources from the carrying asset.LEMS integrates a Mass Spectrometer, a Laser Retro-reflector Array, a Lunar Micrometeoroid Monitor, a Lunar Energetic Ion Analyzer, and a 3-axis Seismometer. These sensors will collect concurrent observations that will lead to a comprehensive, time-resolved, and geographically-localized characterization of the composition and dynamics of volatiles gases in the lunar exosphere as a response to variations in solar forcing, IDP flux, seismicity, and known manmade events. Furthermore, owing to its expected longevity, LEMS will also improve upon the success of the Apollo Passive Seismic Experiment (PSE) by providing a new generation of seismological measurements that will address unanswered questions by the PSEs. These questions include the size and state of the lunar core, homogeneity of the mantle, variation in crustal thickness, the mechanism for deep moonquakes, and the relationship between shallow seismicity and the current tectonic state of the lunar crust.With its complementary and integrated multi-sensors and its autonomous concept of operation, LEMS is a science-enabling investigation that combines capabilities, in a single duplicable instrument package. The duplicative nature of the LEMS design enables a network of stations that focuses on exospheric and geophysical measurements at the Moon to become viable options. Finally, the self-sustaining architecture of LEMS provides a model design of future payloads that can take advantage of more commercial or scientific flight opportunities to the Moon while requiring no further support for operation from their carrying assets.

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.

Introduction. We present the scientific potential for using an Interstellar Probe (ISP) spacecraft traveling to > 500 AU from the Sun to study the dust in the solar system's debris disks and the nearby ISM, as well as to map the surface of a flyby KBO and study the Cosmic Background Light (CBL). Figure 1 – Interstellar Probe Explorer payload at its design goal location of 1000 AU with respect to the planets, the heliopause, Alpha Centauri, and the Oort Cloud. Discussion. The solar system is known to house two planetesimal belts, the inner Jupiter Family Comet (JFC) + Asteroid belt and the outer Edgeworth-Kuiper Belt (EKB), and at least one debris cloud, the Zodiacal Cloud, sourced by planetesimal collisions and comet evaporative sublimation. However, these are poorly understood in toto because we live inside of them. It is not understood well how much dust is produced from the EKB since the near-Sun comet contributions dominate the inner cloud and only New Horizons (NH) has ever flown a dust counter through the EKB. New estimates from NH put the EKB disk mass at at 30 – 40 times the inner disk mass [1]. Better understanding EKB dust production will improve our estimates of the number of EKB bodies, especially the smallest ones, and their dynamical collisional state. For the innermost Zodiacal cloud, questions remain concerning its overall shape and orientation with respect to the invariable plane - these are not explainable from perturbations caused by the known planets alone. Imaging Studies. Using new technologies and passively cooled detectors, a suitable low system size/mass/power VISNIR spectrometer/FIR imager + 10 cm class primary has been specified using a CubeSat study baseline design [2]. The VISNIR spectrometer could provide maps of the cloud's dust particle size and composition, while FIR imagery would map the dust cloud's density. 3-D cloud mapping would occur during flythrough via tomographic inversion, and via lookback imaging once the s/c is beyond 200 AU. The lookback imaging will allow ISP to measure for the 1st time in history the entire extent of the Zodiacal Cloud, and determine whether its inner JFC/asteroidal & outer KBO parts connect smoothly, as predicted by Stark & Kuchner [3-4] and detected by Piquette, Poppe et al. [5-8] (Figs. 2-3). This would also allow direct comparison of the solar system’s debris disks with those observed around other nearby stars, and test theories that suggest that our solar system is planet rich but dust-poor [9]. Figure 2 – Predicted dust cloud morphologies arising from solar system JFC (JFC) & Oort Cloud (OCC) comets & Kuiper Belt (EKB) sources. (Top) Looking down on the solar system. (Bottom) Looking through the plane of the solar system. After [1]. Looking back towards the Sun from >100 AU, ISP will perform deep searches for the presence of rings and dust clouds around discrete sources, like Planet X, the Haumea family of icy collisional fragments, the rings of the Centaur Chariklo, or dust emitted from spallation off the larger KBOs. The same instrument will map the surfaces of KBOs encountered along the way. Measurement of the cloud’s total brightness will allow removal of its signal from near-Earth CBL measurements looking at all the starlight ever formed in the Universe, and the same instrument will return its own remote CBL measurements. Figure 3 – NH in situ measurements (black data pts) and predicted dust flux contributions (colored curves) for the solar system’s debris disks [1,8]. Measured PIONEER 10 dust fluxes are in the upper left corner of the plot, so the predicted crossover at ~10 AU from JFC dominated to EKB dominated is seen. ISP will help us determine if another crossover from EKB dominated to OCC dominated occurs at ~100 AU, and if the EKB dust is ice, rock, & organics rich like KBOs and comets. First Ever Outer Solar System In Situ Dust Characterization. ISP can also carry the first ever in situ dust chemical analyzer past Saturn. Based on the Europa Clipper SUDA instrument [10], it will compositionally and directionally characterize the solar system’s dust clouds and will help isolate their sources, like the rocky asteroidal dust bands and the icy Haumea family fragments. Using measured dust particle masses and velocities, dust input & loss rates from these sources will be derived. Direct dust sampling will return the first ever in situ chemical analysis of EKB dust, the first ever in situ sampling of dust beyond 200 AU, and provide calibrated ground truth for cloud models produced from our imagery. It should also resolve the tension between the expected makeup of inflowing ISM microdust as determined by remote sensing and the mesasured ISM dust component found at Jupiter and Saturn by Galileo, Ulysses, and Cassini ([11] & Figure 4). Understanding a G2V’s Astropause ISM Bowshock. At the outermost solar system edges, the role dust plays in shaping and energizing the heliosphere’s boundary with the local galactic medium is almost completely unknown. Estimates range up to 1/3 of the heliopause and heliosheath energy density is in the dust. Current heliopause/sheath models do not allow for dusty plasma physics because the dust component is so poorly known. We do know that submicron sized dust is streaming into the solar system's ram direction through the local ISM, and the large deficit between remote sensing models of local ISM dust and ISM dust measured inside the solar system suggests a large amount of energy is involved in diverting much of the impinging dust around the edges of the solar system. Figure 4 – Disconnect between the nearby ISM dust size distribution predicted from remote sensing measurements (blue) and ISM dust counts measured inside the solar system (red). After [11]. References: [1] Poppe+2019, ApJLett881, L12 [2] Zemcov+2019, AASMeeting#233, id.#171.06 [3] Stark&Kuchner 2009, ApJ707, 543 [4] Stark&Kuchner 2010, AJ140, 1007 [5] Poppe+2010, Geophys.Res.Lett.37, L11101 [6] Poppe&Horányi 2012, Geophys.Res.Lett. 39, 1 [7] Poppe2016, Icarus264, 369 [8] Piquette+2019, Icarus321, 116 [9] Greaves&Wyatt 2010, MNRAS404, 1944 [10] Kempf+2014, EPSCAbstracts9, EPSC2014-229 [11] Weingartner&Draine, ApJ548, 296; Draine&Hensley 2016, ApJ831, 59

International audience; The Reiner Gamma swirl is a prime location to investigate the lunar albedo patterns and their co‐location with magnetic anomalies. The precise relationship between impinging plasma and the swirl, and in particular, how these interactions vary over the course of a lunar day, remains an open issue. Here we use a fully kinetic particle‐in‐cell code, coupled with a magnetic field model based on orbital‐altitude observations, and simulate the interaction with the Reiner Gamma anomaly for all plasma regimes the region is exposed to along a typical orbit, including different solar wind incidence angles and the Moon's crossing through the terrestrial magnetosphere. Consistent with the hypothesis that swirls form as a result of plasma interactions with near‐surface magnetic fields, we show that the energy flux profile produces a pattern similar to Reiner Gamma's alternating bright and darkly colored bands, but only when integrating over the full lunar orbit. We additionally show that including He2+ as a self‐consistent plasma species improves the match.

Examining Arrokoth The New Horizons spacecraft flew past the Kuiper Belt object (486958) Arrokoth (also known as 2014 MU 69 ) in January 2019. Because of the great distance to the outer Solar System and limited bandwidth, it will take until late 2020 to downlink all the spacecraft's observations back to Earth. Three papers in this issue analyze recently downlinked data, including the highest-resolution images taken during the encounter (see the Perspective by Jewitt). Spencer et al. examined Arrokoth's geology and geophysics using stereo imaging, dated the surface using impact craters, and produced a geomorphological map. Grundy et al. investigated the composition of the surface using color imaging and spectroscopic data and assessed Arrokoth's thermal emission using microwave radiometry. McKinnon et al. used simulations to determine how Arrokoth formed: Two gravitationally bound objects gently spiraled together during the formation of the Solar System. Together, these papers determine the age, composition, and formation process of the most pristine object yet visited by a spacecraft. Science , this issue p. eaay3999 , p. eaay3705 , p. eaay6620 ; see also p. 980

The Reiner Gamma swirl is one of the most prominent albedo features on the lunar surface. Its modest spatial scales and structure allows fully kinetic modelling. The region therefore presents a prime location to investigate the lunar albedo patterns and their co-location with magnetic anomalies. The precise relationship between the impinging plasma and the swirl, and in particular, how these interactions vary over the course of a lunar day, remains an open issue.Here we use the fully kinetic particle-in-cell code, iPIC3D, coupled with a magnetic field model based on Kaguya and Lunar Prospector observations, and simulate the interaction with the Reiner Gamma anomaly for all plasma regimes the region is exposed to along a typical orbit, including different solar wind incidence angles and the Moon's crossing through the terrestrial magnetosphere. We focus on the impact of the solar wind alpha population and construct energy and velocity distributions in key locations surrounding the interaction region of the anomaly.The energy flux profile provides a better match to the albedo pattern only when integrating over the full lunar orbit. Including He2+ as a self-consistent plasma species improves the brightness ratios between the inner and outer bright lobes, the dark lanes, and the mare background. However, substantial differences between the observed albedo pattern and the predicted flux remain. For example, the bright outer lobes are substantially brighter than predicted and the central portion of the anomaly is darker than predicted. This is likely due to an incomplete model of the near-surface field structure.Solar wind standoff can explain the large-scale correlation between the Reiner Gamma swirl and the co-located magnetic anomaly. In particular, the outer bright lobes emerge in the simulated weathering pattern only when integrating over the entire lunar orbit, although they are much weaker than observed. Both the proton and helium energy flux to the surface need to be taken into account to best reproduce the swirl pattern. A complete understanding of the solar wind interaction with lunar magnetic anomalies and swirl formation could be vastly improved by low altitude measurements of the magnetic field and solar wind.

Our understanding of the lunar dust exosphere is based on NASA’s Lunar Atmosphere and Dust Environment Explorer. Its findings provide a unique opportunity to map the composition of the lunar surface from orbit and identify regions that are rich in volatiles, providing opportunities for future in situ resource utilization (ISRU), which is a key element in establishing human habitats on the Moon. The expected availability of water ice, and other volatiles, in Permanently Shadowed Regions (PSR) makes the lunar poles of prime interest. However, the relative strength of the various sources, sinks, and transport mechanisms of water into and out of PSRs remain largely unknown. The quantitative characterization of the temporal and spatial variability of the influx of IDPs to the polar regions of the Moon is critical to the understanding the evolution of volatiles in PSRs. A dust instrument onboard a polar orbiting lunar spacecraft could make fundamental measurements to assess the availability and accessibility of water ice in PSRs. Water is thought to be continually delivered to the Moon through geological timescales by water-bearing comets and asteroids and produced continuously in situ by the impacts of solar wind protons of oxygen-rich minerals on the surface. IDPs are an unlikely source of water due to their long UV exposure in the inner solar system, but their high-speed impacts can mobilize secondary ejecta dust particles, atoms and molecules, some with high-enough speed to escape the Moon. Other surface processes that can lead to mobilization, transport and loss of water molecules and other volatiles include solar heating, photochemical processes, and solar wind sputtering. Since the efficiency of these are reduced in PSRs, dust impacts remain the dominant process to dictate the evolution of volatiles in PSRs.The continually present dust ejecta cloud was observed by LADEE/LDEX. A more capable dust instrument, in addition to the size and speed of an impacting particle, can also measure the composition of secondary ejecta particles, resulting in a surface composition map with a spatial resolution comparable to the height of the spacecraft.This talk will describe the available instrumentation, its testing and calibration using the SSERVI /IMPACT dust accelerator facility at the University of Colorado, Boulder, and conclude with the recognition that a polar-orbiting spacecraft could directly sample lunar ejecta, providing the critical link between IDP bombardment and the evolution of water ice in PSRs.

The zodiacal cloud in the inner solar system undergoes continual evolution, as its dust grains are collisionally ground and sublimated into smaller and smaller sizes. Sufficiently small (~

Antenna instruments on space missions have been used to detect dust particles and characterize dust populations. The antennas register the transient electric signal generated by the expansion of the impact plasma from the dust impact on the spacecraft body or the antenna. Given the large effective sensitive area, antenna instruments offer an advantage over dedicated dust detectors for dust populations with low fluxes. The dust accelerator facility operated at the University of Colorado has been employed to investigate the physical mechanisms of antenna signal generation. The dominant mechanism is related to the charging of the spacecraft (or antenna) by collecting some fraction of electrons and ions from the impact plasma. We have carried out a number of experimental campaigns in order to characterize the dust impact charge yields from relevant materials, the effective temperatures of dust impact plasmas, and variations of the antenna signals with spacecraft potential, or magnetic field. Here we report on a physical model that provides a good qualitative and quantitative description of the antenna waveforms recorded in laboratory conditions. The model is based on the separation of the electrons from the ions in the impact plasma and their different timescales of expansion. The escaping and collected fractions of charges are driven by the spacecraft potential. Fitting the model to the laboratory data revealed that the electrons in the impact plasma have an isotropic distribution, while ions are dominantly moving away from the dust impact location. Identifying the fine details in the antenna signals requires a relatively high sampling rate and thus not commonly resolved for past instruments. The high-rate mode of the FIELDS instrument on the Parker Solar Probe, however, can be used to verify the proposed model.

We used existing data from the New Horizons LORRI camera to measure the optical-band ($0.4\lesssim\lambda\lesssim0.9{\rm\mu m}$) sky brightness within seven high galactic latitude fields. The average raw level measured while New Horizons was 42 to 45 AU from the Sun is $33.2\pm0.5{\rm ~nW ~m^{-2} ~sr^{-1}}.$ This is $\sim10\times$ darker than the darkest sky accessible to the {\it Hubble Space Telescope}, highlighting the utility of New Horizons for detecting the cosmic optical background (COB). Isolating the COB contribution to the raw total requires subtracting scattered light from bright stars and galaxies, faint stars below the photometric detection-limit within the fields, and diffuse Milky Way light scattered by infrared cirrus. We remove newly identified residual zodiacal light from the IRIS $100\mu$m all sky maps to generate two different estimates for the diffuse galactic light (DGL). Using these yields a highly significant detection of the COB in the range ${\rm 15.9\pm 4.2\ (1.8~stat., 3.7~sys.) ~nW ~m^{-2} ~sr^{-1}}$ to ${\rm 18.7\pm 3.8\ (1.8~stat., 3.3 ~sys.)~ nW ~m^{-2} ~sr^{-1}}$ at the LORRI pivot wavelength of 0.608 $\mu$m. Subtraction of the integrated light of galaxies (IGL) fainter than the photometric detection-limit from the total COB level leaves a diffuse flux component of unknown origin in the range ${\rm 8.8\pm4.9\ (1.8 ~stat., 4.5 ~sys.) ~nW ~m^{-2} ~sr^{-1}}$ to ${\rm 11.9\pm4.6\ (1.8 ~stat., 4.2 ~sys.) ~nW ~m^{-2} ~sr^{-1}}$. Explaining it with undetected galaxies requires the galaxy-count faint-end slope to steepen markedly at $V>24$ or that existing surveys are missing half the galaxies with $V< 30.$, Comment: 32 pages, 20 figures. Accepted for publication in ApJ

The outer Solar System object (486958) Arrokoth (provisional designation 2014 MU69) has been largely undisturbed since its formation. We studied its surface composition using data collected by the New Horizons spacecraft. Methanol ice is present along with organic material, which may have formed through irradiation of simple molecules. Water ice was not detected. This composition indicates hydrogenation of carbon monoxide-rich ice and/or energetic processing of methane condensed on water ice grains in the cold, outer edge of the early Solar System. There are only small regional variations in color and spectra across the surface, which suggests that Arrokoth formed from a homogeneous or well-mixed reservoir of solids. Microwave thermal emission from the winter night side is consistent with a mean brightness temperature of 29 ± 5 kelvin. ©2020, NASA (contract no. NASW-02008), NASA (grant no. NAS5-97271 / TaskOrder30)

Electrostatic dust lofting has been suggested to explain a number of unresolved phenomena on airless planetary bodies such as the lunar horizon glow, the dust ponds on asteroid Eros, and the radial ‘spokes’ in Saturn’s rings. In this paper we report laboratory measurements of the size distribution of lofted dust particles in the range of 1 to 40 μ m in diameter. It is shown that the population of lofted dust increases with a decrease in dust size (i.e., smaller sized dust is easier to be lofted), which is in agreement with the theoretical expectation derived from the patched charge model (Wang et al., 2016a). Additionally, initial launch velocities are derived from transport distances of lofted particles following ballistic trajectories. It is shown that the initial velocity of lofted particles is inversely proportional to their size, in agreement with an earlier work that used a different measurement method (Carroll et al., 2020).

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.

Surfaces in space collect charges due to exposure of solar ultraviolet (UV) radiation, electrons, and ions. Throughout the solar system, UV-generated photoelectrons dominate the charging balance and exposed surfaces tend to charge positively. The surface potential of exposed objects depends on the material properties of their surfaces. Composition and particle size primarily affect the quantum efficiency of photoelectron generation; however, surface roughness can also control the charging process. Here we examine the role of surface roughness in generating photoelectrons in dedicated laboratory experiments using solid and dusty surfaces of the same composition. Using Langmuir probe measurements, we explore the measured plasma conditions above insulating surfaces exposed to UV, and we show that the photoemission current from a dusty surface is largely reduced due to its higher surface roughness, which causes a significant fraction of the emitted photoelectrons to be re-absorbed within the surface.