Student Dust Counter Research Articles

Candidate Distant Trans-Neptunian Objects Detected by the New Horizons Subaru TNO Survey

We report the detection of 239 trans-Neptunian objects discovered through the ongoing New Horizons survey for distant minor bodies being performed with the Hyper Suprime-Cam mosaic imager on the Subaru Telescope. These objects were discovered in images acquired with either the r2 or the recently commissioned EB-gri filter using shift and stack routines. Due to the extremely high stellar density of the search region downstream of the spacecraft, new machine learning techniques had to be developed to manage the extremely high false-positive rate of bogus candidates produced from the shift and stack routines. We report discoveries as faint as r2 ∼ 26.5. We highlight an overabundance of objects found at heliocentric distances R ≳ 70 au compared to expectations from modeling of the known outer solar system. If confirmed, these objects betray the presence of a heretofore-unrecognized abundance of distant objects that can help explain a number of other observations that otherwise remain at odds with the known Kuiper Belt, including detections of serendipitous stellar occultations, and recent results from the Student Dust Counter on board the New Horizons spacecraft.

New Horizons Venetia Burney Student Dust Counter Observes Higher than Expected Fluxes Approaching 60 au

The NASA New Horizons Venetia Burney Student Dust Counter (SDC) measures dust particle impacts along the spacecraft’s flight path for grains with mass ≥10−12 g, mapping out their spatial density distribution. We present the latest SDC dust density, size distribution, and flux measurements through 55 au and compare them to numerical model predictions. Kuiper Belt objects (KBOs) are thought to be the dominant source of interplanetary dust particles in the outer solar system due to both collisions between KBOs and their continual bombardment by interstellar dust particles. Continued measurements through 55 au show higher than model-predicted dust fluxes as New Horizons approaches the putative outer edge of the Kuiper Belt (KB). We discuss potential explanations for the growing deviation: radiation pressure stretches the dust distribution to further heliocentric distances than its parent body distribution; icy dust grains undergo photosputtering that rapidly increases their response to radiation pressure forces and pushes them further away from the Sun; and the distribution of KBOs may extend much further than existing observations suggest. Ongoing SDC measurements at even larger heliocentric distances will continue to constrain the contributions of dust production in the KB. Continued SDC measurements remain crucial for understanding the Kuiper Belt and the interpretation of dust disks around other stars.

Student Dust Counter Status Report: The First 50 au

Abstract The Venetia Burney Student Dust Counter (SDC) is an in situ dust detector on board the New Horizons spacecraft measuring the interplanetary dust particle (IDP) distribution for grains with mass m > 10−12 g. SDC provides a near-continuous measure of the interplanetary dust environment, with recent results spanning beyond 50 au. This coverage includes the Edgeworth–Kuiper Belt (EKB), suggested by numerical models to be the dominant source of IDP in the outer solar system. Here we present the updated dust density distribution to 50 au and compare estimated flux values to existing theoretical models. SDC observes peak dust flux and densities near 42 au, and we expect a decay with increasing heliocentric distance. Based on SDC measurements, we also discuss the effects of IDP generation, transport, and loss on the evolution of the surfaces of EKB objects, the continual intermixing of their surface material, and the general tendency to homogenize their spectral properties. Continued SDC measurements remain critical for revealing the large-scale structure of the EKB and to guide the interpretation of dust disks around other stars. Additionally, we consider the potential of an interstellar dust (ISD) and “outer” Kuiper Belt contribution to SDC measurements and its effect on anticipated SDC flux values beyond 50 au, and we show that the inclusion of either source to the predicted model results in a noticeable deviation in anticipated SDC measurements beyond 50 au. Current and future SDC measurements also serve to constrain the relative contribution of ISD to SDC’s flux and density estimates.

Constraining the Solar System's Debris Disk with In Situ New Horizons Measurements from the Edgeworth–Kuiper Belt

Abstract The solar system currently possesses two remnant debris disks leftover from the planetary formation era in the form of the asteroid belt and the Edgeworth–Kuiper Belt (EKB). Similar to other stellar systems, these debris disks continually generate submillimeter-sized dust grains through processes such as mutual collisions, interstellar dust grain bombardment, and sublimation/sputtering of larger grains. Here, we use recent in situ measurements by the New Horizons Student Dust Counter and an interplanetary dust dynamics model to constrain the overall structure and magnitude of the solar system’s debris disk, including the disk mass, optical depth, and surface brightness in both scattered light and thermal emission. We find that ∼99% of the solar system’s dust disk mass (grains with diameter <1 mm) is contained within EKB and Oort Cloud cometary grains outside of 30 au, with the remaining ∼1% mass in the form of Jupiter-family cometary dust within 5 au. The total disk mass is estimated to be ∼8 × 10−7 M ⊕ with a total fractional luminosity of ∼5 × 10−7, confirming our solar system as a relatively dust-poor system compared to debris disks around similar-aged FGK stars. Finally, we estimate that Kuiper Belt Object collisional events such as that which created the Haumea family could transiently increase the current surface brightness of our debris disk by a factor of only ∼6, far less than median brightnesses seen in other nearby disks. This further supports the idea that the EKB has been largely depleted of its primordial mass relative to other stellar systems by instabilities triggered by planetary migration.

Student Dust Counter: Status report at 38 AU

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.

The New Horizons and Hubble Space Telescope search for rings, dust, and debris in the Pluto-Charon system

We conducted an extensive search for dust or debris rings in the Pluto-Charon system before, during, and after the New Horizons encounter in July 2015. Methodologies included attempting to detect features by back-scattered light during the approach to Pluto (phase angle α ∼ 15°), in situ detection of impacting particles, a search for stellar occultations near the time of closest approach, and by forward-scattered light imaging during departure (α ∼ 165°). An extensive search using the Hubble Space Telescope (HST) prior to the encounter also contributed to the final ring limits. No rings, debris, or dust features were observed, but our new detection limits provide a substantially improved picture of the environment throughout the Pluto-Charon system. Searches for rings in back-scattered light covered the range 35,000–250,000 km from the system barycenter, a zone that starts interior to the orbit of Styx, the innermost minor satellite, and extends out to four times the orbital radius of Hydra, the outermost known satellite. We obtained our firmest limits using data from the New Horizons LORRI camera in the inner half of this region. Our limits on the normal I/F of an unseen ring depends on the radial scale of the rings: 2×10−8 (3σ) for 1500 km wide rings, 1×10−8 for 6000 km rings, and 7×10−9 for 12,000 km rings. Beyond ∼ 100, 000 km from Pluto, HST observations limit normal I/F to ∼8×10−8. Searches for dust features from forward-scattered light extended from the surface of Pluto to the Pluto-Charon Hill sphere (rHill=6.4×106 km). No evidence for rings or dust clouds was detected to normal I/F limits of ∼8.9×10−7 on ∼ 104 km scales. Four stellar occulation observations also probed the space interior to Hydra, but again no dust or debris was detected. The Student Dust Counter detected one particle impact 3.6 × 106 km from Pluto, but this is consistent with the interplanetary space environment established during the cruise of New Horizons. Elsewhere in the solar system, small moons commonly share their orbits with faint dust rings. Our results support recent dynamical studies suggesting that small grains are quickly lost from the Pluto-Charon system due to solar radiation pressure, whereas larger particles are orbitally unstable due to ongoing perturbations by the known moons.

Comparative planetary nitrogen atmospheres: Density and thermal structures of Pluto and Triton

Both atmospheres of Pluto and Neptune's largest satellite Triton have cold surfaces with surface gravitational accelerations and atmospheric surface pressures of comparable magnitude. To study their atmospheres we have updated Zhu et al. (2014) model for Pluto's atmosphere by adopting Voigt line profiles in the radiation module with the latest spectral database and extended the model to Triton's atmosphere by including additional parameterized heating due to the magnetospheric electron transport and energy deposition. The CH4 mixing ratio profiles play central roles in differentiating the atmospheres of Pluto and Triton. On Pluto the surface CH4 mole fraction is in the range of 0.3-0.8%, sufficiently high to ensure that it is well mixed in the lower atmosphere and not subject to photochemical destruction. Near the exobase CH4 attains comparable density to N2 due to gravitational diffusive separation and escapes at 500 times the N2 rate (= 1 × 1023 N2s−1). In Triton's atmosphere, the surface CH4 mole fraction is on the order of 0.015%, sufficiently low to ensure that it is photochemically destroyed irreversibly in the lower atmosphere and that N2 remains the major species, even at the exobase. With solar EUV power only, Triton's upper thermosphere is too cold and magnetospheric heating, approximately comparable to the solar EUV power, is needed to bring the N2 tangential column number density in the 500–800km range up to values derived from the Voyager 2 UVS observations (Broadfoot et al., 1989). Due to their cold exobase temperatures relative to the gravitational potential energy wells that N2 resides in, atmospheric escape from Triton and Pluto is not dominated by N2 Jeans escape but by CH4 from Pluto and H, C, N and H2 from Triton. The atmospheric thermal structure near the exobase is sensitive to the atmospheric escape rate only when it is significantly greater than 2×1027amus−1, above which enhanced Jeans escape and larger radial velocity adiabatically cools the atmosphere to a lower temperature. Finally we suggest that Pluto's thermosphere is a cold ∼ 70K due to ablation of H2O molecules from the influx of dust grains detected by New Horizons Student Dust Counter.

An improved model for interplanetary dust fluxes in the outer Solar System

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 10AU, Oort-Cloud cometary grains may dominate between 10 and 25AU, and Edgeworth-Kuiper Belt grains are dominant outside 25AU. 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 1AU. Finally, we compare the model predictions of interplanetary dust oxygen influx to the giant planet atmospheres with various observational and photochemical constraints and generally find good agreement, with the exception of Jupiter, which suggests the possibility of additional chemical pathways for exogenous oxygen in Jupiter’s atmosphere.

Interplanetary dust influx to the Pluto–Charon system

The influx of interplanetary dust grains (IDPs) to the Pluto–Charon system is expected to drive several physical processes, including the formation of tenuous dusty rings and/or exospheres, the deposition of neutral material in Pluto’s atmosphere through ablation, the annealing of surface ices, and the exchange of ejecta between Pluto and its satellites. The characteristics of these physical mechanisms are dependent on the total incoming mass, velocity, variability, and composition of interplanetary dust grains; however, our knowledge of the IDP environment in the Edgeworth-Kuiper Belt has, until recently, remained rather limited. Newly-reported measurements by the New Horizons Student Dust Counter combined with previous Pioneer 10 meteoroid measurements and a dynamical IDP tracing model have improved the characterization of the IDP environment in the outer Solar System, including at Pluto–Charon. Here we report on this modeling and data comparison effort, including a discussion of the IDP influx to Pluto and its moons, and the implications thereof.

The Student Dust Counter: Status report at 23 AU

The Student Dust Counter (SDC) is an impact dust detector on board the New Horizons Mission to Pluto. SDC was designed to resolve the mass of dust grains in the range of 10−12 < m < 10−9 g, covering an approximate size range of 0.5–10 μm in particle radius. The measurements can be directly compared to the prediction of a grain trajectory tracing model of dust originating from Edgeworth-Kuiper Belt (EKB). Comparing our measurements and model prediction is used to estimate the net mass production rate and the ejecta mass distribution power law exponent to be and , respectively. Through April 2012, the New Horizons spacecraft reached approximately 23 AU, enabling SDC to map the dust density distribution along its path.

Cratering studies in Polyvinylidene Fluoride (PVDF) thin films

Thin, permanently polarized Polyvinylidene Fluoride (PVDF) films have been used as dust detectors on a number of missions including the Dust Counter and Mass Analyzer (DUCMA) instrument on Vega 1 and 2 to comet 1P/Halley, the High Rate Detector (HRD) on the Cassini Mission to Saturn, the Student Dust Counter (SDC) on New Horizons to Pluto, the Dust Flux Monitor Instrument (DFMI) on the Stardust mission to comet 81P/Wild 2, the Space Dust (SPADUS) instrument on the Earth orbiting Advanced Research and Global Observation Satellite (ARGOS) and the Cosmic Dust Experiment (CDE) on the Aeronomy of Ice in the Mesosphere (AIM) mission in orbit around the Earth. Due to their low power requirements and light weight, large surface area detectors can be built for observing low dust fluxes. The operation principle behind metal-coated PVDF detectors is that a micrometeorite impact removes a portion of the metal surface layer, exposing the permanently polarized PVDF dielectric underneath. This changes the local electric potential near the crater, and the surface charge of the metal layer, which can be recorded as a transient current. The dimensions of the crater determine the strength of the potential change and thus the signal generated by the PVDF. Currently used scaling laws relating impactor parameters to crater geometry, which are used to predict PVDF response, are suspected to have systematic errors. Work is being undertaken to develop a new crater diameter scaling law using iron particles in PVDF. Cratered samples are analyzed using a 3D reconstruction technique using stereo image pairs taken in a Scanning Electron Microscope (SEM) and cross sections taken in a Focused Ion Beam (FIB). We report on the details of the reconstruction techniques and the initial findings of the crater parameter scaling law study.

Constraints on dust production in the Edgeworth-Kuiper Belt from Pioneer 10 and New Horizons measurements

[1] Impact ejecta and collisional debris from the Edgeworth-Kuiper Belt are the dominant source of micron-sized grains in the outer solar system, as they slowly migrate inwards through the outer solar system before most grains are ejected during close encounters with Jupiter. These grains drive several phenomena in the outer solar system, including the generation of impact ejecta clouds at airless bodies, the formation of ionospheric layers and neutral gases in the atmospheres of the giant planets due to meteoric ablation, the generation of tenuous outer planetary ring systems and the spatial and compositional alteration of Saturn's main rings. Previous analyses have offered estimates of the net mass production rate from the Edgeworth-Kuiper Belt both theoretically and observationally. In order to improve upon these estimates, we compare measurements of the interplanetary dust density in the outer solar system by both the Pioneer 10 meteoroid detector and the New Horizons Student Dust Counter with a dynamical dust grain tracing model. Our best estimates for the net mass production rate and the ejecta mass distribution power law exponent are (8.9 ± 0.5) × 105 g/s and 3.02 ± 0.04, respectively.

Simulation of polyvinylidene fluoride detector response to hypervelocity particle impact

Polyvinylidene fluoride (PVDF) films have been utilized as interplanetary dust detectors for many years in a variety of space environments. PVDF serves as a dust detector by producing a ‘depolarization’ charge upon hypervelocity impact. Previous instruments have relied on empirical calibrations to establish the relationship between the mass and velocity of the impacting dust particle and the generated charge. Here, we present a new theoretical derivation of PVDF response to non-penetrating hypervelocity particle impacts. We compare our simulation results to experimental calibration data from the Cosmic Dust Experiment on the Aeronomy of Ice in the Mesosphere satellite and the Student Dust Counter on the New Horizons mission. The simulation results agree well with the experimental data, yet suggest a modified crater diameter scaling law for non-penetrating hypervelocity impacts into PVDF.

First results from the Venetia Burney Student Dust Counter on the New Horizons mission

The Venetia Burney Student Dust Counter (SDC) onboard the New Horizons mission is an impact‐based dust detector designed to map the size and spatial variability of the interplanetary dust population throughout the solar system. SDC consists of fourteen permanently polarized polyvinylidene fluoride detectors that register a charge upon impact by hypervelocity dust grains. SDC can resolve the masses of grains with 10−12 &lt; m &lt; 10−9 g and measurements to date extend from 2.6 to 15.5 AU. SDC dust flux measurements taken inside the orbit of Jupiter are compared to previous measurements by the Ulysses and Galileo dust detectors to validate the instrument. Measurements taken outside Jupiter's orbit, spanning 6.8 AU to 15.5 AU, are also reported and compared with measurements by the Pioneer 10 and 11 meteoroid detectors and the Voyager 1 and 2 plasma wave instruments.

Polyvinylidene fluoride dust detector response to particle impacts

Polyvinylidene fluoride (PVDF) dust detectors have flown on many space missions since their first use on the Vega 1 and 2 spacecraft. The fundamental operating principle of these detectors is the production of a charge upon impact by a hypervelocity dust particle. This measured signal, N, depends on the speed, v, and mass, m, of the particle. The relationship between N, v, and m was first empirically derived by Simpson and Tuzzolino. All of the PVDF dust instruments prior to the Student Dust Counter on the New Horizons mission use their formula for the calibration of the detectors. This paper provides additional dust impact calibration data, proposes a modification in the exponents for m and v, and investigates the relationship between detector temperature and detector signal.

Overview of the New Horizons Science Payload

The New Horizons mission was launched on 2006 January 19, and the spacecraft is heading for a flyby encounter with the Pluto system in the summer of 2015. The challenges associated with sending a spacecraft to Pluto in less than 10 years and performing an ambitious suite of scientific investigations at such large heliocentric distances (>32 AU) are formidable and required the development of lightweight, low power, and highly sensitive instruments. This paper provides an overview of the New Horizons science payload, which is comprised of seven instruments. Alice provides moderate resolution (∼3–10 A FWHM), spatially resolved ultraviolet (∼465–1880 A) spectroscopy, and includes the ability to perform stellar and solar occultation measurements. The Ralph instrument has two components: the Multicolor Visible Imaging Camera (MVIC), which performs panchromatic (400–975 nm) and color imaging in four spectral bands (Blue, Red, CH4, and NIR) at a moderate spatial resolution of 20 μrad/pixel, and the Linear Etalon Imaging Spectral Array (LEISA), which provides spatially resolved (62 μrad/pixel), near-infrared (1.25–2.5 μm), moderate resolution (λ/δ λ∼240–550) spectroscopic mapping capabilities. The Radio Experiment (REX) is a component of the New Horizons telecommunications system that provides both radio (X-band) solar occultation and radiometry capabilities. The Long Range Reconnaissance Imager (LORRI) provides high sensitivity (V<18), high spatial resolution (5 μrad/pixel) panchromatic optical (350–850 nm) imaging capabilities that serve both scientific and optical navigation requirements. The Solar Wind at Pluto (SWAP) instrument measures the density and speed of solar wind particles with a resolution ΔE/E<0.4 for energies between 25 eV and 7.5 keV. The Pluto Energetic Particle Spectrometer Science Investigation (PEPSSI) measures energetic particles (protons and CNO ions) in 12 energy channels spanning 1–1000 keV. Finally, an instrument designed and built by students, the Venetia Burney Student Dust Counter (VB-SDC), uses polarized polyvinylidene fluoride panels to record dust particle impacts during the cruise phases of the mission.

The Student Dust Counter on the New Horizons Mission

The Student Dust Counter (SDC) experiment of the New Horizons Mission is an impact dust detector to map the spatial and size distribution of dust along the trajectory of the spacecraft across the solar system. The sensors are thin, permanently polarized polyvinylidene fluoride (PVDF) plastic films that generate an electrical signal when dust particles penetrate their surface. SDC is capable of detecting particles with masses m>10−12 g, and it has a total sensitive surface area of about 0.1 m2, pointing most of the time close to the ram direction of the spacecraft. SDC is part of the Education and Public Outreach (EPO) effort of this mission. The instrument was designed, built, tested, integrated, and now is operated by students.