Modeling the Altitude Distribution of Meteor Head Echoes Observed with HPLA Radars-Implications on the Radar Detectability of Meteoroid Populations

The altitude distribution of meteors detected by a radar is sensitive to the instrument's response function and can thus provide insight into the physical processes involved in radar measurements. This, in turn, can be used to determine the rate of ablation and ionization of the meteoroids and ultimately the input flux on Earth. In this work, we model the radar meteor head echo altitude distribution for three High Power and Large Aperture radar systems, by considering meteoroid populations from the main cometary family sources. In this simulation, we first use the results of a dynamical model of small meteoroids impacting Earth's upper atmosphere to model the incoming mass, velocity, and entry angular distributions. We then combine these with the Chemical Ablation Model and establish the meteoroid ionization rates as a function of mass, velocity, and entry angle in order to determine the altitude at which these radars should detect the produced meteors and the portion of produced meteors from each population that are detected by these radars. We explore different sizes of head plasma as well as the possible effects on radar scattering of the head echo aspect sensitivity. We find that the modeled altitude distributions are generally in good agreement with measurements, particularly for ultra-high-frequency radars. In addition, our results indicate that the number of particles from Jupiter Family Comets (JFCs) required to fit the observations is lower than predicted by astronomical models. It is not clear yet if this discrepancy is due to the overprediction of JFC meteoroids by dynamical models or due to unaccounted physical processes in the treatment of ablation, ionization, and detections of meteoroids as they pass through Earth's atmosphere

Differential ablation of organic coatings from micrometeoroids simulated in the laboratory

Micrometeoroids contain organic material that may undergo differential ablation during atmospheric entry, potentially depositing organic material into Earth's atmosphere and affecting the radar detectability of meteors. To investigate the differential ablation of organics, we used a dust accelerator to shoot submicron polypyrrole-coated olivine particles at speeds of 10–20 km/s into a gas target containing air. A set of biased electrodes placed along the path of the particles measured the charges generated when the particles ablated and the ablated molecules collided with gas molecules. We observed that the particles differentially ablate their organic polypyrrole coatings prior to their inorganic olivine cores, producing spikes in charge production, with charge yields of 104–105 C/kg even at relatively low speeds. These measurements suggest that large organic molecules survived ablation and are responsible for the observed charge production since small molecules either do not produce ions at those speeds or produce them in much lower quantities than observed. We modeled the ablation using basic meteor physics by assuming that the polypyrrole coating decomposes into pyrrole monomer. Extending these results to the ablation of micrometeoroids in the atmosphere indicates that organic coatings should ablate at high altitudes within relatively narrow altitude ranges, which has consequences for the detectability of meteors by radar. Since the ablated coatings generate relatively large molecules, the results also suggest that micrometeoroids can deliver complex organic material into planetary atmospheres by ablating them during entry, potentially serving as a source of prebiotic organics

Impact ionization mass spectra of anorthite cosmic dust analogue particles

Anorthite, the Ca-rich end-member of plagioclase feldspar, is a dominant mineral component of the Lunar highlands. Plagioclase feldspar is also found in comets, meteorites and stony asteroids. It is therefore expected to contribute to the population of interplanetary (and circumplanetary) dust grains within the solar system. After coating micron- and submicron-sized grains of Anorthite with a conductive layer of Platinum, the mineral was successfully accelerated to hypervelocity speeds in the Max Planck Institut für Kernphysik’s Van de Graaff accelerator. We present impact ionization mass spectra generated following the impacts of anorthite grains with a prototype mass spectrometer (the Large Area Mass Analyser, LAMA) designed for use in space, and discuss the behavior of the spectra with increasing impact energy. Correlation analysis is used to identify the compositions and sources of cations present in the spectra, enabling the identification of several molecular cations (e.g., CaAlO2, CaSiO2, Ca2AlO3/CaAlSi2O2) which identify anorthite as the progenitor bulk grain material

Using Dust Shed from Asteroids as Microsamples to Link Remote Measurements with Meteorite Classes

Given the diversity of asteroids, it is impossible to consider returning samples from each one Dust particles are abundant around asteroids Primary minerals and organic materials can be measured by in situ dust detectorinstruments These particles can be used to classify the parent body as an ordinary chondrite,basaltic achondrite, or other class of meteorite Such instruments could provide direct links to known meteorite groups withoutreturning the samples to terrestrial laboratorie

LADEE Science Results and Implications for Exploration

NASA's Lunar Atmosphere and Dust Environment Explorer, LADEE, concluded a fully successful investigation of the Moon's tenuous gas and dust atmosphere on April 18, 2014. LADEE hosted three science instruments to address atmospheric and dust objectives, and a technology demonstration of deep-space optical communication. The three science instruments were an ultraviolet-visible spectrometer (UVS), a neutral mass spectrometer (NMS), and a lunar dust experiment (LDEX). All data acquired by these instruments have been submitted to the Planetary Data System. A mission overview and science instrument descriptions are readily available. LADEE inserted into a low-altitude, retrograde lunar orbit optimized for observations at the sunrise terminator, where surface temperatures rise abruptly. LADEE also carried out observations over a wide range of local times and altitudes. Here we describe some of the initial results

Synergies between interstellar dust and heliospheric science with an interstellar probe

We discuss the synergies between heliospheric and dust science, the open science questions, the technological endeavours, and programmatic aspects that are important to maintain or develop in the decade to come. In particular, we illustrate how we can use interstellar dust in the solar system as a tracer for the (dynamic) heliosphere properties, and emphasize the fairly unexplored, but potentially important science question of the role of cosmic dust in heliospheric and astrospheric physics. We show that an interstellar probe mission with a dedicated dust suite would bring unprecedented advances to interstellar dust research, and can also contribute – through measuring dust – to heliospheric science. This can, in particular, be done well if we work in synergy with other missions inside the solar system, thereby using multiple vantage points in space to measure the dust as it ‘rolls’ into the heliosphere. Such synergies between missions inside the solar system and far out are crucial for disentangling the spatially and temporally varying dust flow. Finally, we highlight the relevant instrumentation and its suitability for contributing to finding answers to the research questions

PADME (Phobos and Deimos and Mars Environment): A Proposed NASA Discovery Mission to Investigate the Two Moons of Mars

PADME is a proposed NASA Discovery mission to investigate the origin of two remarkable and enigmatic small bodies, Phobos and Deimos, the two moons of Mars