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  • Planetary and Space Science
  • 1
    Language: English
    In: Planetary and Space Science, December 2013, Vol.89, pp.2-14
    Description: One of the unresolved enigmas from the Apollo era is the existence and characteristics of highly electrically charged dust floating above the lunar surface. Potential evidence for this hypothesized phenomenon came from the Lunar Ejecta and Meteorites (LEAM) experiment on Apollo 17. The LEAM instrument consisted of three sets of multi-coincidence dust sensors facing different directions. Recently, new arguments were raised ( ) that the signals recorded by LEAM may be caused by interferences from heater current switching, which occurred most frequently near sunrise and sunset. In order to shed light on this controversy a new look into the LEAM data was initiated within the Colorado Center for Lunar and Dust and Atmospheric Studies (CCLDAS) team of NASA's Lunar Science Institute (NLSI). The purpose of this analysis is to verify the earlier analysis by , and to find evidence for impacts of interplanetary meteoroids in the LEAM data available to us. A second goal is to find in the LEAM house keeping data evidence for excessive power switching and correlated signals in the LEAM science data. The original analysis by covered LEAM data during 22 lunations (~22 months) in 1973 and 1974. This data set is no longer available. For the present study, we had access to LEAM data for only about 5 lunations (140 days) in 1976. We analyzed the housekeeping data and observed excessive heating from about 24 h after sunrise until about 24 h before sunset. We defined sunrise and sunset when the LEAM temperature measurement reached −20 °C above which significant solar heating was apparent. For about 9 days around lunar noon the temperatures were so high that LEAM was switched off. During the times of excessive heating LEAM became very noisy. We limit our current analysis to about 24 h before sunset to about 24 h after sunrise when the LEAM temperatures were moderate 〈60 °C. This carefully analyzed data set of 74.6 days constitutes about 75% of the periods when LEAM was switched on in 1976. We did not find a systematic correlation between the infrequent heater switches and the occurrence of signals. During the lunar night the temperature was quite stable at approx. −25 °C. One TOF dust impact event and 19 potential dust events were recorded by all three sensors during the periods when the instrument was at moderate temperatures. This corresponds to an average event rate of 0.25/day. While nine events are compatible with a random occurrence the other 10 events occurred in three statistically significant bursts within about 1 h or less after another. Two bursts occurred within the middle of lunar night and one burst of three events was recorded by the West sensor just an hour before sunrise. The background rates are compatible with impact rates recorded by the dust instruments onboard the Pioneer 8 and 9 spacecraft in interplanetary space. Based on our definition of sunrise and sunset, the 1976 LEAM data do not indicate strongly enhanced dust activity at the terminator.
    Keywords: Lunar Dust ; Leam ; Apollo17 Data Analysis ; Engineering ; Astronomy & Astrophysics ; Physics
    ISSN: 0032-0633
    E-ISSN: 1873-5088
    Source: ScienceDirect Journals (Elsevier)
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  • 2
    Language: English
    In: Planetary and Space Science, 2011, Vol.59(14), pp.1672-1680
    Description: Each year the Moon is bombarded by about 10 kg of interplanetary micrometeoroids of cometary and asteroidal origin. Most of these projectiles range from 10 nm to about 1 mm in size and impact the Moon at 10–72 km/s speed. They excavate lunar soil about 1000 times their own mass. These impacts leave a crater record on the surface from which the micrometeoroid size distribution has been deciphered. Much of the excavated mass returns to the lunar surface and blankets the lunar crust with a highly pulverized and “impact gardened” regolith of about 10 m thickness. Micron and sub-micron sized secondary particles that are ejected at speeds up to the escape speed of 2300 m/s form a perpetual dust cloud around the Moon and, upon re-impact, leave a record in the microcrater distribution. Such tenuous clouds have been observed by the Galileo spacecraft around all lunar-sized Galilean satellites at Jupiter. The highly sensitive Lunar Dust Experiment (LDEX) onboard the LADEE mission will shed new light on the lunar dust environment. LADEE is expected to be launched in early 2013. Another dust related phenomenon is the possible electrostatic mobilization of lunar dust. Images taken by the television cameras on Surveyors 5, 6, and 7 showed a distinct glow just above the lunar horizon referred to as horizon glow (HG). This light was interpreted to be forward-scattered sunlight from a cloud of dust particles above the surface near the terminator. A photometer onboard the Lunokhod-2 rover also reported excess brightness, most likely due to HG. From the lunar orbit during sunrise the Apollo astronauts reported bright streamers high above the lunar surface, which were interpreted as dust phenomena. The Lunar Ejecta and Meteorites (LEAM) Experiment was deployed on the lunar surface by the Apollo 17 astronauts in order to characterize the lunar dust environment. Instead of the expected low impact rate from interplanetary and interstellar dust, LEAM registered hundreds of signals associated with the passage of the terminator, which swamped any signature of primary impactors of interplanetary origin. It was suggested that the LEAM events are consistent with the sunrise/sunset-triggered levitation and transport of charged lunar dust particles. Currently no theoretical model explains the formation of a dust cloud above the lunar surface but recent laboratory experiments indicate that the interaction of dust on the lunar surface with solar UV and plasma is more complex than previously thought. ► Interplanetary and interstellar meteoroids hit the lunar surface. ► Impacts of meteoroids release high speed ejecta particles. ► Electrostatic effects mobilizes charged lunar dust. ► Moon is enshrouded by a cloud of dust particles.
    Keywords: Moon ; Dust Flux ; Microcraters ; Impact Ejecta ; Horizon Glow ; Electrostatic Dust Transport ; Engineering ; Astronomy & Astrophysics ; Physics
    ISSN: 0032-0633
    E-ISSN: 1873-5088
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  • 3
    Language: English
    In: Planetary and Space Science, 15 December 2015, Vol.119, pp.173-180
    Description: The performance of the Nano-Dust Analyzer (NDA) instrument is analyzed for close pointing to the Sun, finding the optimal field-of-view (FOV), arrangement of internal baffles and measurement requirements. The laboratory version of the NDA instrument was recently developed ( ) for the detection and elemental composition analysis of nano-dust particles. These particles are generated near the Sun by the collisional breakup of interplanetary dust particles (IDP), and delivered to Earth׳s orbit through interaction with the magnetic field of the expanding solar wind plasma. NDA is operating on the basis of impact ionization of the particle and collecting the generated ions in a time-of-flight fashion. The challenge in the measurement is that nano-dust particles arrive from a direction close to that of the Sun and thus the instrument is exposed to intense ultraviolet (UV) radiation. The performed optical ray-tracing analysis shows that it is possible to suppress the number of UV photons scattering into NDA׳s ion detector to levels that allow both high signal-to-noise ratio measurements, and long-term instrument operation. Analysis results show that by avoiding direct illumination of the target, the photon flux reaching the detector is reduced by a factor of about 10 . Furthermore, by avoiding the target and also implementing a low-reflective coating, as well as an optimized instrument geometry consisting of an internal baffle system and a conical detector housing, the photon flux can be reduced by a factor of 10 , bringing it well below the operation requirement. The instrument׳s FOV is optimized for the detection of nano-dust particles, while excluding the Sun. With the Sun in the FOV, the instrument can operate with reduced sensitivity and for a limited duration. The NDA instrument is suitable for future space missions to provide the unambiguous detection of nano-dust particles, to understand the conditions in the inner heliosphere and its temporal variability, and to constrain the chemical differentiation and processing of IDPs.
    Keywords: Nano-Dust ; Interplanetary Dust Particles ; Solar Uv Radiation ; Bidirectional Reflectance Distribution Function ; Engineering ; Astronomy & Astrophysics ; Physics
    ISSN: 0032-0633
    E-ISSN: 1873-5088
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  • 4
    Language: English
    In: Planetary and Space Science, 15 December 2015, Vol.119, pp.185-193
    Description: The lunar surface is continuously exposed to the micrometeoroid environment. Hypervelocity impacts of interplanetary dust particles with speeds around generate secondary ejecta on the lunar surface. A dust detector placed on the moon is capable of characterizing the secondary ejecta population. The purpose of this paper is to study the speed and trajectory information of ejecta by impact simulations and its implications for the location of a dust sensor on the surface. AUTODYN15.0/2D software was used to simulate the velocity and angular distributions of ejecta created by the primary impacts of interplanetary dust particles. We considered projectiles with sizes of spheres in diameter with speeds of . We used impact angles of 15°, 30°, 45°, 60°, 75°, and 90° with respect to the surface. A significant percentage of the impact ejecta are created in the early-time stage of the impact process. This population can be captured by a sensor placed on the lunar surface (e.g. Lunar Ejecta and Meteorites (LEAM) experiment) or by a sensor mounted directly on a lander (e.g. Lunar Dust eXplorer (LDX)). The secondary ejecta population above the lunar surface is considered to explain the results of the LEAM experiment. A sensor directly placed on the surface like LEAM is not very well suited to measure the high-speed ejecta component – a sensor located at a few meters height (e.g. on top of a lunar lander) would measure higher fluxes.
    Keywords: Lunar Dust ; Impact Ejecta ; Dust Sensor ; Leam ; Ldx ; Autodyn ; Engineering ; Astronomy & Astrophysics ; Physics
    ISSN: 0032-0633
    E-ISSN: 1873-5088
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  • 5
    Language: English
    In: Planetary and Space Science, December 2013, Vol.89, pp.29-35
    Description: 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.
    Keywords: Cratering ; Pvdf ; Dust Detectors ; Engineering ; Astronomy & Astrophysics ; Physics
    ISSN: 0032-0633
    E-ISSN: 1873-5088
    Source: ScienceDirect Journals (Elsevier)
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  • 6
    Language: English
    In: Planetary and Space Science, December 2013, Vol.89, pp.63-70
    Description: We report the advance development of the Electrostatic Lunar Dust Analyzer (ELDA) instrument for the detection of individual low-velocity micron-size dust particles mobilized near the lunar surface, and the measurement of the dust charge, velocity vector, and mass. The first article ( ) described the measurement principle, optimized instrument geometry, and the initial testing performed on air. The full laboratory prototype of ELDA has now been completed and tested under vacuum. The numerical data analysis is improved to include gravitation and the calculation of the particle's mass. The ELDA operation principle is based on sensing a charged dust particle by an array of wire electrodes as it is passing though the instrument. Each wire electrode is connected to a charge sensitive amplifier and the velocity vector is reconstructed from the signal shapes and amplitudes. Within the instrument, a strong electrostatic field is used to deflect the trajectories of the particles. The dust mass is determined from the change in velocity measured before and after deflection. The instrument is tested using particles with 54 μm mean radius and a narrow size distribution. The experimental results and the error analyses show that ELDA can measure the mass of individual particle with a factor of two even for very low signal to noise ratio. ► Electrostatic Lunar Dust Analyzer (ELDA) instrument has been built. ► We improve the numerical data analysis of ELDA. ► ELDA is tested under vacuum using calibrated dust particles. ► ELDA can measure the mass of individual particle with a factor of two.
    Keywords: Moon Dust ; Mass Measurement ; Charge Induction ; Trajectory Sensor ; Engineering ; Astronomy & Astrophysics ; Physics
    ISSN: 0032-0633
    E-ISSN: 1873-5088
    Source: ScienceDirect Journals (Elsevier)
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  • 7
    Language: English
    In: Planetary and Space Science, October 2011, Vol.59(13), pp.1446-1454
    Description: Micron and submicron-sized dust particles can be lifted from the lunar surface due to continual micrometeoroid bombardment and electrostatic charging. The characteristics of these dust populations are of scientific interest and engineering importance for the design of future equipment to operate on the lunar surface. The mobilized grains are expected to have a low velocity, which makes their detection difficult by traditional methods that are based on momentum transfer or impact energy. We describe a newly developed instrument concept, the Electrostatic Lunar Dust Analyzer (ELDA), which utilizes the charge on the dust for detection and analysis. ELDA consists of an array of wire electrodes combined with an electrostatic deflection field region, and measures the mass, charge, and velocity vector of individual dust grains. The first basic prototype of the ELDA instrument has been constructed, tested and characterized in the laboratory. The instrument is set up to measure over a velocity range 1–100 m/s and is sensitive to particles from an approximate mass range from 2×10 to 10 kg, depending on the charge state and velocity. ► Dust may be levitated near the lunar surface by meteoroid bombardment or electrostatic forces. ► An instrument is designed and prototype built for the detection an analysis. ► Testing is performed in laboratory conditions. ► The data are analyzed and show that low noise and good performance is achieved.
    Keywords: Moon ; Dust ; Dust Charge ; Charge Induction ; Trajectory Sensor ; Engineering ; Astronomy & Astrophysics ; Physics
    ISSN: 0032-0633
    E-ISSN: 1873-5088
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  • 8
    Language: English
    In: Planetary and Space Science, 2011, Vol.59(14), pp.1815-1825
    Description: Classical methods to analyze the surface composition of atmosphereless planetary objects from an orbiter are IR and gamma ray spectroscopy and neutron backscatter measurements. The idea to analyze surface properties with an in-situ instrument has been proposed by . There, it was suggested to analyze Europa's thin atmosphere with an ion and neutral gas spectrometer. Since the atmospheric components are released by sputtering of the moon's surface, they provide a link to surface composition. Here we present an improved, complementary method to analyze rocky or icy dust particles as samples of planetary objects from which they were ejected. Such particles, generated by the ambient meteoroid bombardment that erodes the surface, are naturally present on all atmosphereless moons and planets. The planetary bodies are enshrouded in clouds of ballistic dust particles, which are characteristic samples of their surfaces. In situ mass spectroscopic analysis of these dust particles impacting onto a detector of an orbiting spacecraft reveals their composition. Recent instrumental developments and tests allow the chemical characterization of ice and dust particles encountered at speeds as low as 1 km/s and an accurate reconstruction of their trajectories. Depending on the sampling altitude, a dust trajectory sensor can trace back the origin of each analyzed grain with about 10 km accuracy at the surface. Since the detection rates are of the order of thousand per orbit, a spatially resolved mapping of the surface composition can be achieved. Certain bodies (e.g., Europa) with particularly dense dust clouds, could provide impact statistics that allow for compositional mapping even on single flybys. Dust impact velocities are in general sufficiently high at orbiters about planetary objects with a radius 〉1000 km and with only a thin or no atmosphere. In this work we focus on the scientific benefit of a dust spectrometer on a spacecraft orbiting Earth's Moon as well as Jupiter's Galilean satellites. This ‘dust spectrometer' approach provides key chemical and isotopic constraints for varying provinces or geological formations on the surfaces, leading to better understanding of the body's geological evolution. ► Moons are enshrouded by dust lifted from micro-meteroid bombardment. ► Analyze dust particles as samples of planetary surfaces at flyby's or from orbiter. ► Dust detectors allow Time-of-Flight spectrometry and dust trajectory reconstruction. ► Compositional mapping of surfaces with ~10 km accuracy and trace compound sensitivity. ► High scientific benefit from dust spectrometers at Moon and Galilean satellites.
    Keywords: Moon ; Europa ; Ganymede ; Dust ; Surface Composition ; Spectrometry ; Engineering ; Astronomy & Astrophysics ; Physics
    ISSN: 0032-0633
    E-ISSN: 1873-5088
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  • 9
    Language: English
    In: Planetary and Space Science, October 2012, Vol.71(1), pp.142-146
    Description: The JUpiter ICy moons Explorer (JUICE) is an ESA L-class mission concept designed to explore the Galilean satellites of the Jovian system. Although the current mission science goals do not include any astrophysical observations, we find that the planned period of the JUICE mission is optimal for in situ measurements of Interstellar Dust (ISD), due to highly increased flux levels at that time. In case that JUICE carries a dust detector, this could lead to in situ high-resolution mass spectra of ISD grains. Such compositional information on the ISD grains is important for understanding the origins of solar/planetary systems, and therefore could represent a valuable addition to the core JUICE mission science. ► Interstellar dust flux predictions for the JUICE mission. ► The interstellar dust flux at Jupiter is at maximum around 2029 at JUICE orbit insertion. ► A dust instrument on the JUICE mission contributes greatly to the mission science goals. ► The JUICE mission is an excellent opportunity to capture high-resolution spectra of ISD grains on top of the core science goals.
    Keywords: Interstellar Dust ; Juice Mission ; Engineering ; Astronomy & Astrophysics ; Physics
    ISSN: 0032-0633
    E-ISSN: 1873-5088
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  • 10
    Language: English
    In: Planetary and Space Science, 2010, Vol.58(1), pp.108-115
    Description: In order to clarify the dust environment around Mercury, we have proposed that the Mercury dust monitor (MDM) should be onboard the BepiColombo/Mercury magnetosphere orbiter (MMO). The main objective of the project is to obtain new data on the flux and momentum of the interplanetary meteoroid complex near Mercury (0.31–0.47 AU). The MDM uses lightweight and heat-resistant piezoelectric ceramic sensors made of lead zirconate titanate (PZT). Four square plates of PZT, 40 mm×40 mm×2 mm each, will be installed on a side panel of the MMO. Upon colliding with a dust particle, the piezoelectricity of PZT generates a transient voltage signal. It is easy to determine the time of the impact event from which the incident direction is roughly estimated using the spin angle of the MMO. To extract kinetic information on incident particles from the output signals of the PZT sensor, calibration experiments have been carried out with hypervelocity dust particles from two Van de Graaff dust accelerators at the Max-Planck-Institut für Kernphysik and the University of Tokyo.
    Keywords: Bepicolombo Mission ; Mercury ; Cosmic Dust ; Piezoelectric Ceramic Sensor ; Engineering ; Astronomy & Astrophysics ; Physics
    ISSN: 0032-0633
    E-ISSN: 1873-5088
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