Laboratory for Atmospheric and Space Physics (LASP) and the Institute for Modeling Plasma, Atmospheres and Cosmic Dust (IMPACT) will be hosting the Dusty Visions Workshop July 22-24, 2016
in Boulder, Colorado, USA at the LASP facilities. We plan on having a discussion heavy workshop on the current studies and future direction of cosmic dust research.
The deadline for registration will be May 1st, and the deadline for abstract submission will be June 1st. We plan on having a cost of $90, for the full
three days, paid in cash at the door. This will include a small breakfast, coffee, tea, lunch, and snacks for all three days, and one dinner.
Eberhard Grün, The 19 Feb. 2016 Outburst of Comet 67P/CG: A Rosetta Multi-Instrument Study
On 19 Feb. 2016 nine Rosetta instruments serendipitously observed an outburst of gas and dust from the nucleus of comet 67P/Churyumov-Gerasimenko. Among these instruments were cameras and spectrometers ranging from UV over visible to microwave wavelengths, in-situ gas, dust and plasma instruments, and one dust collector. At 9:40 a dust cloud developed at the edge of an image in the shadowed region of the nucleus. Over the next two hours the instruments recorded a signature of the outburst that significantly exceeded the background. The enhancement ranged from 50% of the neutral gas density at Rosetta to factors >100 of the brightness of the coma near the nucleus. Dust related phenomena (dust counts or brightness due to illuminated dust) showed the strongest enhancements (factors >10). However, even the electron density at Rosetta increased by a factor 3 and consequently the spacecraft potential changed from ~-16 V to -20$ V during the outburst. A clear sequence of events was observed at the distance of Rosetta (34 km from the nucleus): within 15 minutes the Star Tracker camera detected fast particles (~25 m\s) while 100 micron radius particles were detected by the GIADA dust instrument ~1 hour later at a speed of 6 m\s. The lowest were individual mm to cm sized grains observed by the OSIRIS cameras. Although the outburst originated just outside the FOV of the instruments, the source region and the magnitude of the outburst could be determined.
Harald Krueger, Dust Impact Monitor (SESAME-DIM) Measurements at Comet 67P/Churyumov-Gerasimenko
The Philae lander carried the Dust Impact Monitor (DIM) on board, which was part of the Surface Electric Sounding and Acoustic Monitoring Experiment (SESAME). DIM employs piezoelectric PZT sensors to detect impacts by sub-millimeter and millimeter-sized ice and dust particles emitted from the nucleus and transported into the cometary coma. The sensor measured dynamical data like flux and the directionality of the impacting particles. Mass and speed of the grains can be constrained for assumed density and the elastic modulus of the grains.
DIM was operated during Philae's descent to its nominal landing site Agilkia and detected one particle impact at an altitude of approximately 2.4 km from the nucleus surface. This is the closest ever dust detection at a cometary nucleus by a dedicated in-situ dust detector. Laboratory calibration experiments performed with compact and porous cometary analogue materials showed that the detected particle had a low bulk density of approximately 250 kg m^3 , and a radius of about 1 mm. The measured parameters can be understood in the context of a simple gas flow model. At Philae's final landing site, Abydos, DIM detected no dust impact which may be due to low cometary activity in the vicinity of Philae, or due to shading by obstacles close to Philae, or both.
Thomas Stephan, Isotope analysis with CHILI-the Chicago Instrument for Laser Ionization
After several years of designing and building the Chicago Instrument for Laser Ionization (CHILI) at the University of Chicago, we obtained the first analytical results from presolar silicon carbide (SiC) grains and calcium-, aluminum-rich inclusions (CAIs). CHILI is a resonance ionization mass spectrometry (RIMS) instrument, designed for isotopic and elemental analyses at high special resolution and high sensitivity. Atoms are released from a sample either by ion sputtering or laser desorption. The cloud of neutrals is then intersected by several laser beams generated by Ti:sapphire lasers precisely tuned to electronic resonances for element-specific ionization. The six Ti:sapphire lasers in CHILI allow for resonance ionization of two or three elements simultaneously. As an initial demonstration, we had analyzed presolar SiC grains for their isotopic compositions of strontium, zirconium, and barium, three elements particularly important for understanding the slow neutron capture process (s-process) in asymptotic giant branch (AGB) stars and, as it turned out, important for understanding nucleosynthesis in type II supernovae. Subsequently, we focused our research on the analysis of iron and nickel isotopes in presolar SiC. While the neutron-rich iron and nickel isotopes in presolar grains from AGB stars are mainly dominated by the s-process in the star, the neutron-poor isotopes can be used to study the galactic chemical evolution. We also studied iron and nickel isotopes in grains from type II supernovae to learn more about supernova nucleosynthesis. We were able, for the first time, to measure all stable iron and nickel isotopes simultaneously without interferences, which is impossible with, e.g., secondary ion mass spectrometry (SIMS). The isobaric interference between 58Fe and 58Ni is resolved in CHILI by delaying the nickel ionization lasers by 200 ns relative to the iron ionization lasers. This time difference corresponds to a mass difference of ~0.5 u in the time-of-flight mass spectra at the specific mass range, sufficient to easily resolve the interference. We recently extended our analyses to iron and nickel isotopes in hibonite-rich CAIs from CM chondrites, which have the largest nucleosynthetic anomalies of all materials believed to have formed inside the Solar System. In the future, we also want to study interplanetary dust particles (IDPs) and samples from the Stardust and Genesis space missions with CHILI for isotopes of these and many other elements.
Bernd Abel, Towards a laser driven ice particle accelerator for laboratory support of space missions: Concept, realization, and specifications
A novel concept of a laser driven ice particle accelerator will be given. An infrared (IR) high power laser is employed to excite and disperse a flat liquid water jet in vacuum. The droplets freeze due to rapid evaporative cooling. Their size is measured via light scattering to be around 300nm. The speed of the heavy particles between 2000 and 5000 m/s are measured in a time-of-flight setup in vacuum, in which light particles are separated from the heavier ones. The concept, its realization, and the obtained specifications, as well as its value for future and past space missions will be highlighted and discussed.
Jonas Simolka, A Compact Single Stage Light Gas Gun for your Desk
The set up of a single stage gas driven accelerator - a so called light gas gun - is planned at the University of Stuttgart in order to extend the accessible range of electrostatic dust accelerators towards higher masses and lower velocities. The accelerator is based on an existing build at the Center for Astrophysics, Space Physics & Engineering Research (CASPER) at Baylor University in Texas [1]. The compact design requires less space then an office desk. The system is designed to operate at pressures of up to 300 Bar by utilizing a standard industrial gas cylinder as the main pressure reservoir for the driving gas. The performance is defined by the maximum achievable velocity, which depends strongly on the molecular weight of the driving gas. Helium provides the best compromise between an achievable muzzle speed and necessary safety precautions (in case of hydrogen). A fast acting solenoid in combination with a rupture disc integrated into the sabot enables the sudden release of the pressurized gas. The sabot is accelerated by the expanding gas until it hits the stopping mechanism at the end of the barrel. The particle(s) are released and the sabot seals the experiment chamber from trailing gas.
Scope: The single stage light gas gun provides the possibility to accelerate sub-millimeter and micron sized particles to velocities of up to ~1000 m/s under controlled conditions. Possible contaminations can only originate from the driving gas itself or the material of the sabot. The parameters of both are relatively easy for the user to control. This is a significant asset for mass spectroscopy and supports development and calibration of time of flight mass spectrometers under well defined laboratory conditions. The generation of icy ejecta as projectiles with an even greater velocity range is conceivable. There are no constraints on the properties of the particles that can be accelerated, particular in the conductivity and shape.
Joseph Schwan, Dust charging and transport on airless planetary bodies
Dust charging, mobilization and transport have been suggested to explain a variety of unusual planetary surface phenomena, including the lunar horizon glow, the dust ponds on asteroid Eros and comet 67P, and the spokes in Saturn's rings. However, as of yet, the exact electrostatic release mechanisms remained a mystery. Current charging models do not explain the results of these in-situ observations.
In this we will report on laboratory experiments that shed light on electrostatic dust transport. Having recorded micron-sized insulating dust jumping several centimeters high with an initial speed ~ 0.5 m/s under ultraviolet (UV) illumination or exposure to plasmas, we experimentally show that the interactions of the insulating dusty surface with UV radiation and/or plasmas are a volume effect. This is contrary to current studies that only consider the interacting surface as a plane boundary. We have determined that the emission and re-absorption of photo- and/or secondary electrons at the walls of micro-cavities, which are formed between neighboring dust particles below the surface, is responsible for generating the unexpectedly large charges that produce the particle-particle repulsive forces which mobilize dust particles.
New results from the direct measurements for the charge of dust particles on the surface will also be presented.
Zoltan Sternovsky, Dust impact detection by antenna instruments - a laboratory investigation
Antenna-based detection of dust grains by spacecraft is a valuable mechanism to enhance the science return from existing missions, and conduct serendipitous observations of interplanetary dust by spacecraft not equipped with dedicated dust instruments. In principle, the detection mechanism is simple: dust grains encountering the spacecraft at high relative speeds undergo ionization upon impact and some fraction of the resulting charged particles is recollected on the spacecraft body or antenna resulting in a measurable signal. However, there is a large uncertainty in calculating the mass of the dust particle from the impact signal. In order to enhance our understanding of the dust impact signals, a series of supporting laboratory measurements have been conducted using the dust accelerator facility at the University of Colorado. In the first set of measurements the impact charge yield for common spacecraft materials were determined. The second campaign investigated the basic signal-generating mechanisms. We found that the three mechanisms (spacecraft charting, antenna charging, antenna pickup) depend on the geometric arrangement as well as the bias potentials of the elements. In the third set, we determined that the effective temperature of the impact plasma is lower than previously reported in the literature, and is increasing with impact speed. Our current focus is the study of impact signal generation by the Cassini spacecraft. For this a 20:1 reduced size model of Cassini has been constructed. The three Radio Plasma Wave Science (RPWS) antennas are configured either in a dipole or a monopole mode. The preliminary measurements support the recent suggestion that most dust detection events recorded in the dipole mode are due to antenna hits, as opposed to impacts on the spacecraft body.
David Malaspina, The Wind Dust Database: 22 Years of Interplanetary and Interstellar Dust Observations at 1 AU
The Wind spacecraft has operated near 1 AU since 1994, but it was only recently discovered that Wind electric field measurements contain observations of interplanetary and interstellar dust. We report on the creation of a publicly accessible Wind dust database which catalogs over 100,000 dust grains observed by Wind during its 22 year mission. The long duration and high daily count rate of the Wind dust database offers a novel and unique opportunity to study the dynamics of interplanetary and interstellar dust at 1 AU over two full solar cycles. We will discuss the database contents and creation methodology, as well as in-situ detection of dust grains by electric field instruments on the Wind spacecraft.
Diego Janches, Radar Detectability of meteor head echoes and its implication on the Zodiacal Dust Cloud populations
The total amount of meteoric input in the upper atmosphere is a hotly debated quantity, which estimates vary by 2 orders of magnitude, depending on measuring techniques. The majority of the input is in the form of microgram size particles, which, in most cases, completely ablate injecting metals in the mesosphere. These metals are the primordial material for most of the layered phenomena (LP) occurring in the mesospause region (MR). Accurate knowledge of this quantity is crucial for the study of LPMR and in many cases it can contribute to the improvement of Whole Atmosphere Models (WAM) by constraining parameters such as vertical transport in the middle atmosphere. In an effort that ultimately aims to estimate this quantity, we utilize a combination of Zodiacal Dust Cloud (ZDC) models that follows the dynamical evolution of dust particles after ejection utilizing the orbital properties of Jupiter Family (JFC) and Halley Type (HTC) Comets and asteroids. In addition, we couple these astronomical models with comprehensive description of meteoroid ablation, ionization and radar detection and thus enable accurate interpretation of radar observations of head echoes obtained with various High Power and Large Aperture (HPLA) Radars. This approach enables us to address potential biases that could, in principle, prevent ground-based instrumentation to detect a portion of the incoming flux and thus better estimate the role that each dust population plays in the total cosmic dust input.
The Earth and the Moon are constantly bombarded by interplanetary meteoroids. While meteoroids turn into shooting stars at Earth due to the thick atmosphere, the Moon's surface is completely exposed. Impacts from the meteoroids onto the lunar surface are continually generating dust ejecta. The Lunar Dust Experiment (LDEX) was an impact ionization dust detector onboard the Lunar Atmosphere and Dust Environment Explorer (LADEE) mission, designed to measure impact ejecta. LDEX observed a permanently present, asymmetric dust cloud engulfing the Moon.
The lunar dust density distribution in the equatorial plane was found to be primarily generated by three known sporadic sources: the helion (HE), apex (AP), and anti-helion (AH). During several of the well characterized annual meteor showers, LDEX observed local enhancements in the dust cloud, particularly during the Geminids. Stream parameters such as the peak flux time and radiant direction can be extracted for certain meteoroid streams. Additionally, we derive an average lunar dust density distribution and calculate the rate at which exospheric dust rains back down onto the lunar surface, gardening it over time.
Characterizing the spatial and temporal variability of the dust environment of airless planetary bodies provides a novel way to understand their meteoroid environment by using these objects as large surface area meteoroid detectors. Measurements from similar dust detectors near the moons Phobos and Deimos would greatly improve our knowledge of the Martian meteoroid environment, and improve the safety for future manned and unmanned missions to Mars. In this presentation, we describe the recently measured lunar dust exosphere in the context of understanding the meteoroid environment at 1 AU.
Andrew Poppe, An improved model for interplanetary dust grain fluxes to the outer planets
We present an improved model for interplanetary dust grain fluxes in the outer solar system constrained by in-situ dust density observations. A dynamical dust grain tracing code is used to establish relative dust grain densities and three-dimensional velocity distributions in the outer solar system for four main sources of dust grains: Jupiter-family comets, Halley-type comets, Oort-Cloud comets, and Edgeworth-Kuiper Belt objects. Model densities are constrained by in-situ dust measurements by the New Horizons Student Dust Counter, the Pioneer 10 meteoroid detector, and the Galileo Dust Detection System (DDS). The model predicts that Jupiter-family comet grains dominate the interplanetary dust grain mass flux inside approximately 10 AU, Oort-Cloud cometary grains may dominate between 10 and 25 AU, and Edgeworth-Kuiper Belt grains are dominant outside 25 AU. The model also predicts that while the total interplanetary mass flux at Jupiter roughly matches that inferred by the analysis of the Galileo DDS measurements, mass fluxes to Saturn, Uranus, and Neptune are at least one order-of-magnitude lower than that predicted by extrapolations of dust grain flux models from 1 AU. Finally, we present modeled mass fluxes to various moons, atmospheres, and ring systems of the outer planets.
Rachel Soja, Collisional implementation for an interplanetary dust model
The Enhanced Interplanetary Meteoroid Population Model is an ESA funded project to develop a model of the interplanetary background dust for spacecraft impact hazard studies. This is envisaged as an improvement of the current ESA Interplanetary Meteoroid Environment Model (IMEM). This existing model is is constrained by various in-situ and infrared observations, but several simplifications in the implementation mean that it is unable to provide a full interpretation of the background cloud. The new model will include dynamical evolution over several 100 000 years of cometary and asteroidal dust populations of particles with sizes 10 microns to 1 cm in the inner solar system, including a collisional model as well as standard gravitational and radiation forces. Here we describe initial activities for the project, including description of initial populations, and the expected next steps for the model. In particular, we describe the development of a collisional destruction model, based on the work of Grün et al. (1985), in order to provide collisional lifetimes encompass the dynamical history of different types of particles. We use the interplanetary background model given by IMEM to provide the impactor population, and trace how the collisional lifetime varies as a function of the orbital elements of the dust particle.
Xiaodong Liu, Dynamics of dust particles from Amalthea and Thebe in the Jovian ring
In this work, the dynamics of dust particles from Amalthea and Thebe in the Jupiter ring system are investigated. The important perturbation forces are considered in our model, including the Lorentz force, solar radiation pressure, solar gravity perturbation, the satellites' gravity perturbations, plasma drag, Poynting-Robertson drag, and the high degree terms of Jovian gravity. The precession rates of argument of pericenter and longitude of ascending node of Amalthea and Thebe are included in the model. A large number of dust particles of different grain sizes starting from the orbits of Amalthea and Thebe are simulated over a maximum of 10,000 years until each of them hits a sink. The reason for the variations of semi-major axis is explained. The distributions of semi-major axis, eccentricity and inclination are analyzed. The locations of Lorentz resonances for micron-sized particles are calculated analytically, which is well consistent with numerical results. We found that dust particles from Amalthea and Thebe can be transported both inwards and outwards. Besides, sub-micron sized particles from Amalthea and Thebe can even contribute to the region of the Galilean moons. While for large particles, it is shown that they can stay in the vicinity of the source moons for quite a long time. The dust configurations in the gossamer ring region obtained from the numerical results are presented, and are compared with the Galileo image.
Thomas Albin, The Dust Orbit Computation Code (DOCC) - A Monte-Carlo based program to determine orbit dynamical properties of Cassini Cosmic Dust Analyzer (CDA) detections
Since 2004 the Cassini spacecraft has been investigating Saturn and its complex system of rings and moons. One of Cassini's instruments is the Cosmic Dust Analyzer (CDA), a dust grain detecting telescope that analyzes the dust environment in Saturn's vicinity (Srama et al. 2004). In particular, CDA has provided detailed analyses of the density profile of the E-Ring (Kempf et al. 2008, Postberg et al. 2008), ISD particles and their chemical composition (Altobelli et al. 2016) and the origin of the ice ejecta from the moon Enceladus (Kempf et al. 2009). Based on a computational model by Soja et al. (2015), who calculated the flight parameters of dust grain impacts on the Galileo Dust Detector, we present a new Monte-Carlo based approach to determine the orbital elements of CDA dust measurements. The "Dust Orbit Computation Code" (DOCC) developed in this project is a Python-based, multi-CPU program that uses laboratory calibration data, the effective area as a function of the impact angle of the instrument, and the measured parameters of dust grains in Saturn's vicinity to compute flight dynamical properties for each impact. We generated an SQLite database containing all orbital information for further scientific investigations. This is useful for determining the origin of the grains, for comparing the structure of the E-Ring with models, or for understanding the interplanetary and interstellar influx into Saturn's system.
Ralph Lorenz, Cassini RADAR Ring-Plane Crossing Impact EMP Experiment
During the Cassini mission's Proximal Orbit endgame, the spacecraft crosses the ring plane close to Saturn and so for spacecraft safety, is oriented with its 4-m High-Gain Antenna towards the ram direction, such that the dish shields the spacecraft's instruments and systems from potential impacts.
It has been observed in laboratory experiments, and anecdotal Earth-orbiting spacecraft anomaly data suggest, that high-speed dust impacts can cause electromagnetic emissions via thermal and nonthermal mechanisms. Since observations can be made with little operational impact, it is proposed to operate the microwave (Ku-band, 13.6 GHz) receiver of the Cassini RADAR instrument during one or more ring-plane crossings in order to detect possible emissions (i.e. impact 'flash' or 'EMP'). Relevant experience and current observing plans will be reviewed, but the results of this exploratory experiment are difficult to predict, as the specific materials/speed/particle size parameters combined with microwave observation have not been replicated in systematic laboratory experiments to date.
Ralf Srama, Dust occultation at Titan measured by CDA onboard Cassini
The Cosmic Dust Analyzer (CDA) onboard Cassini characterized successfully the dust environment at Saturn since 2004. The instrument measures the primary charge, speed, mass and composition of individual submicron and micron sized dust grains. The detection threshold scales with speed^3.5 such that the detection of fast nanograins (~100 km/s) is possible. Saturn's nanodust environment (streams) is studied many years. However, a special geometric condition of Saturn, Cassini and Titan during a Titan flyby in 2014 (DOY 65) provided a special dust occultation opportunity. Titan and its atmosphere blocked the stream of fast nanoparticles such that CDA registered a clear drop in impact rate around closest approach. An analysis of the data allows to constrain the source region of the nanograins, which is compatible with a source region in the ring plane at distances from Saturn between 4 and 8 Saturn radii. Backward and forward modeling was performed leading to dust grain sizes between 3 and 9 nm and speeds between 80 and 150 km/s. The new modeling results also show that Enceladus acts a direct source for nanodust streams leading to the observation of periodic impact rates in the outer Saturn system. Such periodicities were observed recently by CDA and showed a clear signature of the Enceladus orbital period. A second dust occultation opportunity using Titan is planned august 2016.
Nozair Khawaja, Latest CDA results on the compositional profile of Enceladus' plume
The Chemical Analyzer (CA) subsystem of CDA produces cationic TOF mass spectra of the ice particles impinging onto the instrument’s target. Three distinct families of the mass spectra have already been identified representing three populations of Enceladus ice particles: i) Almost pure water - Type-1 ii) Organic enriched - Type-2 and iii) Salt rich - Type-3 [1,2].
Although over 100.000 mass spectra have been recorded in the E ring only on very few occasions spectra have been acquired directly in the Enceladian plume. Only on one flyby in 2008 (E5) statistics were sufficient to infer a compositional profile. The profile implies that the contributions of different compositional populations in the plume vary with altitude [3].
We will present the latest CDA data on compositional mapping of the Enceladian plume on Cassini Enceladus flybys E17, E18 & E21 that occurred in 2012 and 2015. The spacecraft horizontally passed through the dense plume region with a closest approach (75 km at E17/18 and 49 km at E21) directly above Enceladus’ South Polar Terrain (SPT). The relative speed of the E17/E18 Enceladus encounters was 7.5 km/s, whereas it was 8.5 km/s during E21.
A Boxcar Analysis (BCA) is performed for the compositional mapping of Enceladus' plume along the spacecraft trajectory [4]. We compare our recent data with the E5 flyby, which was executed at much higher velocity (~17.6 km/s) and a very different, highly inclined, flyby geometry [3]. On E17 and E18 the abundances of different compositional types of ice particles differ from the Ering background confirming the compositional differentiation inside the plume [4] but also showing profound differences. Currently the data analysis of E21 is in progress for the comparison.
Frank Postberg, Organic compounds from Enceladus in the E ring
Water ice dominates the composition of the micron and sub-micron sized dust particles in Saturn's E-ring, a ring constantly replenished by active icy jets of the moon Enceladus. Details about the composition of this tenuous, optically thin ring can only be constrained by in situ measurements. The Cosmic Dust Analyzer (CDA) onboard Cassini investigates the composition of these grains by cationic time-of-flight mass spectra of individual ice grains hitting the instruments target surface. From these spectra three compositional types of E ring ice grains have been identified previously: Type-1: Almost pure water, Type-2: Enriched in organics, and Type-3: Enriched in salt.
Unlike Type-1 and 3, organic-enriched Type-2 spectra have not yet been investigated in depth. Here we report a detailed compositional analysis of this type. The spectra analysis is supported by a large-scale laboratory ground campaign in Heidelberg yielding a library of analogue spectra for organic material embedded in a water ice matrix. As expected, we find more complex and refractory organic molecules in ice grains compared to the volatile organic material in the gas phase. In contrast to Type 1 and 3, Type-2 spectra display a great compositional diversity, which indicates varying contributions of several organic species. So far we have identified characteristic fragment patterns of at least three classes of organic compounds: aromatic species, amines, and carbonyl group species. The diversity of the identified species requires different generation scenarios for different organic bearing ice grains. We discuss these scenarios and give and outlook to our future work.
Arsen Dzhanoev, Kinetic Processes in the Enceladus Vents
We study the possibility of dust aggregation and fragmentation processes when icy grains are transported to space by water vapor streams in the subsurface vents of Saturn's active moon Enceladus [1]. Depending on their shape the dust aggregates, or non-spherical dust grains, can establish higher equilibrium charges than a spherical grain of the same mass when exposed to equivalent charging conditions. This indicates that dust charging models with spherical grains lead to a net charge underestimation. This effect in combination with small particle effect [2], [3] might be important if one likes to verify if dust charging can account for the misfit between ion and electron densities inferred from data taken by the Cassini-Langmuir probe in the E ring and in the Enceladus plume [5]. Furthermore, an increased charge-to-mass ratio, and a reduced bulk density for dust in Saturn's inner magnetosphere will affect the dynamics of these grains in the E ring region. This will modify the size-dependent lifetimes of particles, which ultimately determine the steady state size- distribution of E ring grains. [1] Schmidt. J. et al. (2008) Nature, 451, 685. [2] Dzhanoev A. R., Schmidt J. et al. (2016) A∓A,
DOI:10.1051/0004-6361/201527891 (arXiv:1603.08565). [3] Dzhanoev A. R., Spahn F. et al. (2015) PRB, 92, 125430 (arXiv:1605.00637). [4] Dzhanoev A. R., et al. (2014) EPSC Abstracts, 9, #755. [5] Wahlund J.-E., et al. (2009) Planetary & Space Sci., 57, 1795.
Steven Cranmer, Predictions for Dusty Mass Loss from Asteroids during Close Encounters with Solar Probe Plus
The Solar Probe Plus (SPP) mission will explore the Sun's corona and innermost solar wind starting in 2018. The spacecraft will also come close to a number of Mercury-crossing asteroids with perihelia less than 0.3 AU. At small heliocentric distances, these objects may begin to lose mass, thus becoming "active asteroids" with comet-like comae or tails. This paper assembles a database of 97 known Mercury-crossing asteroids that may be encountered by SPP, and it presents estimates of their time-dependent visible-light fluxes and mass loss rates. Assuming a similar efficiency of sky background subtraction as was achieved by STEREO, we find that approximately 80% of these asteroids are bright enough to be observed by the Wide-field Imager for SPP (WISPR). A model of gas/dust mass loss from these asteroids is developed and calibrated against existing observations. This model is used to estimate the visible-light fluxes and spatial extents of spherical comae. Observable dust clouds occur only when the asteroids approach the Sun closer than 0.2 AU. The model predicts that during the primary SPP mission between 2018 and 2025, there should be 113 discrete events (for 24 unique asteroids) during which the modeled comae have angular sizes resolvable by WISPR. The largest of these correspond to asteroids 3200 Phaethon, 137924, 155140, and 289227, all with angular sizes of roughly 15 to 30 arcminutes. We note that the SPP trajectory may still change, but no matter the details there should still be multiple opportunities for fruitful asteroid observations.
Thomas Albin, The Canary Islands Long-Baseline Observatory (CILBO) - 3 years of stereoscopic meteor observations
The Canary Islands Long-Baseline Observatory (CILBO), run by the Meteor Research Group (MRG) at ESA-ESTEC, has continuously observed meteors since January 2013 (Koschny et al. 2013). The automatic observatory consists of two separate optical systems located on the islands of Tenerife and La Palma. These stations observe an overlapping part of the sky between both islands that allows stereoscopic observation and orbit determination of detected meteors. An additional camera with an optical grid provides spectroscopic data that provides an analysis of the chemical composition. CILBO data for 2013-2015 has been used to produce a database of over 15,000 simultaneously observed meteors, containing both shower meteors and meteors from the sporadic background. Here we provide an overview of 3 years of CILBO meteor research activities. We present studies of the unbiased mass influx at the Earth (Ott et al. 2014, Kretschmer et al. 2015, Drolshagen et al. 2015), of the velocity distribution of the observed meteors (Drolshagen et al. 2014), and of bias effects that result from the camera pointing (Albin et al. 2015a). Furthermore, we present a Monte-Carlo based orbit determination program based on the Meteor Orbit and Trajectory Software (Koschny & Diaz 2002) that utilizes unbiased velocity determination methods (Albin et al. 2015b). An overview of the resulting orbit database will also be given.
Yanwei Li, Experimental studies of impact ionization detector based on the design of LDEX
A well designed electrostatic field is always needed for the impact ionization detector to separate and accelerate the generated ions/electrons. One of the normally used design methods is employing a bowl shaped impact target together with a hemispherical focus grid. We present both simulation and experimental results of the induced charge signals measured by an impact ionization detector based on the design of the Lunar Dust Experiment (LDEX). These induced charge signals are used to address the particle charge, and more important, the impact positions of dust grains on the bowl shaped target. The energy and angular distributions of impact generated ions and electrons were also studied.
Ethan Williams, Simulation and optimization of the ion optics of reflecting TOF spectrometers
Time-of-flight (TOF) mass spectrometers that incorporate a reflecting field can be both high-performance and space-efficient, making them a valuable class of instruments for a variety of space missions. We discuss the physical design and methods of simulation and optimization for two such instruments. For the first type, the classic reflectron, the problem of optimization is analytically solved. The second type, a large area instrument such as HyperDust or the Surface Dust Analyzer (SUDA), differs from the classic reflectron in that they rely on the ability to focus ions from a large, disk-shaped target area to a central detector. The large target area makes it possible to have a large flux of dust into the instrument at the cost of having to set up the nonlinear focusing field, thus compromising performance. We present our approach to parameterizing the structural and electrical configurations of spectrometers, our evaluation of simulated instrument performance, and our nuanced line of thought that guides the optimization process.
Bill Goode, Hypervelocity Dust Trajectories Measured by the Dust Coordinate Sensor at IMPACT
The Dust Coordinate Sensor (DCS) is a dual-location instrument installed on the beamline of the of dust accelerator at the Institute for Modeling Plasma, Atmospheres and Cosmic Dust (IMPACT) at the University of Colorado. This instrument measures the individual trajectories of charged, hypervelocity (3-5 km/s), micron-sized dust particles while in flight. In order to calculate trajectories, DCS records the x-y coordinates of each particle at two locations along the beamline, 4 m apart. The coordinate measurements utilize the image charge induced by each dust particle as is passes through two 24 mm^2 grids of wire electrodes. The resulting peak voltages of each wire are measured by charge sensitive amplifiers (CSAs) and compared to a series of lookup tables (created using COULOMB simulations) via interpolation software in order to determine the x-y coordinate at each grid's location. The coordinate measurements are matched by timestamp with separate measurements of charge and velocity for each launched dust particle. Real-time information on individual particles' positions anywhere along the beamline as well as aggregate statistics such as beam width and position can thus be determined. Future applications of DCS will include studies of impact craters on a variety of targets; the DCS will enable one-to-one matching of individual craters with specific particle characteristics (mass, velocity), even in targets impacted by many particles in a given experiment.
Evan Thomas, Measurements of Simulated Micrometeoroids in the Laboratory
Each day, several tons of meteoric material enters Earth's atmosphere, with the majority of this material consisting of small dust particles that completely or partially ablate at high altitudes. This large influx of dust particles has been suggested to play a role in a variety of atmospheric phenomena, but it also provides the opportunity to directly measure the dust environment around the Earth. Such measurements have the potential to improve hazard mitigation models for future missions as well as provide important data for better understanding the evolution of the inner solar system. Various methods are used to detect and measure the properties of the meteors depending on their size. Meteor radars are one such method that is sensitive to the most important mass regime in terms of daily mass input (10-9 – 10-3 g), but there are large uncertainties in the ablation process which lead to uncertainties in the radar measurements. The dust accelerator facility at the SSERVI Institute for Modeling Plasma, Atmospheres and Cosmic Dust (IMPACT) has implemented an experiment that allows for the simulation of micrometeroid ablation in the laboratory. A pressurized ablation chamber is fitted to the end of the dust accelerator and acts as a proxy atmosphere for the accelerated dust particles. The pressure is monitored by an absolute pressure gauge and can be pressurized from 15-500 mTorr with a variety of gases. The design of the ablation chamber expands on previous experimental efforts and contains a suite of electronics capable of measuring the generated plasma along the entire ablation trajectory with a spatial resolution of 2.6 cm. This allows for a direct measurement of the ionization coefficient, β, which is a critical parameter for interpreting radar measurements. It also allows for the verification of the basic physics in commonly used ablation models. Here we report on new measurements of the ionization coefficient for iron micrometeoroids impacting N2, air, CO2, and He gases. Our results indicate potential problems with using the commonly used β values for interpreting ablation data for CO2 atmospheres (like Mars) and for high-speed meteors on Earth. This can lead to incorrect assessments of hazards as well as misleading data used in models of the inner solar system evolution.
Marcus Piquette, Interplanetary Dust from Earth to the Kuiper Belt: Results from the Student Dust Counter
The Student Dust Counter (SDC) is an impact dust detector onboard the New Horizons spacecraft, observing the dust density distribution since April 2006 across the Solar System. SDC measures the mass of dust grains in the range of 10-12 - 10-9 g, covering an approximate size range of 0.5-5 μm in particle radius. Measurements can be compared to recent models following the orbital evolution of dust grains originating from the Edgeworth-Kuiper Belt. The measurements SDC has taken throughout the solar system, including in the Pluto-Charon system, are presented, as well as predictions for the dust distribution it will measure as it explores the Kuiper Belt.
