The challenges in hypervelocity microphysics research on meteoroid impacts into the atmosphere

Meteor science contributes greatly to the study of the Solar System and the Earth's atmosphere. However, despite its importance and very long history, meteor science still has a lot to explore in the domain of meteor plasma microphysics and the meteor-ionosphere interaction. Meteors are actually a difficult target for high-resolution observations, which leads to the need for more ambitious interdisciplinary observational setups and campaigns. We describe some recent developments in the physics of meteor flight and microphysics of meteor plasma and argue that meteor science should be fully integrated into the science cases of large astronomical facilities.Peer reviewe

Determination of strewn fields for meteorite falls

When an object enters the atmosphere it may be detected as a meteor. A bright meteor, called a fireball, may be a sign of a meteorite fall. Instrumentally observed meteorite falls provide unique opportunities to recover and analyse unweathered planetary samples supplemented with the knowledge on the Solar system orbit they had. To recover a meteorite from a fireball event, it is essential that recovery teams can be directed to a well-defined search area. Until recently, simulations showing the realistic mapping of a strewn field were difficult, in particular due to the large number of unknowns not directly retrieved from the fireball observations. These unknowns include the number of fragments and their aerodynamic properties, for which the masses of the fragments need to be assumed in a traditional approach. Here, we describe a new Monte Carlo model, which has already successfully assisted in several meteorite recoveries. The model is the first of its kind as it provides an adequate representation of the processes occurring during the luminous trajectory coupled together with the dark flight. In particular, the model comprises a novel approach to fragmentation modelling that leads to a realistic fragment mass distribution on the ground. We present strewn field simulations for the well-documented Kosice and Neuschwanstein meteorite falls, which demonstrate good matches to the observations. We foresee that our model can be used to revise the flux of extra-terrestrial matter onto the Earth, as it provides a possibility of estimating the terminal mass of meteorite fragments reaching the ground.Peer reviewe

Partial Decoding of the GPS Extended Prediction Orbit File

Publisher Copyright: © 2021 FRUCT.The paper is concerned with decoding the Extended Prediction Orbit data format file for an Assisted-GPS web-service via cypher-text only attack. We consider mandatory data content of the file and reveal the changes of this content at different moments. The frequency of changes hints at the location of records for current GPS date and satellite orbits information. Comparing the repeating data patterns against reference orbits information, we obtain the meaning of data fields of the orbit record for each operational satellite. The partially deciphered GPS almanac data layout is provided as a table within the paper.Peer reviewe

Partial decryption of the GPS extended prediction orbit file

The paper is concerned with decoding the Extended Prediction Orbit data format file for an Assisted-GPS web-service via cypher-text only attack. We consider mandatory data content of the file and reveal the changes of this content at different moments. The frequency of changes hints at the location of records for current GPS date and satellite orbits information. Comparing the repeating data patterns against reference orbits information, we obtain the meaning of data fields of the orbit record for each operational satellite. The partially deciphered GPS almanac data layout is provided as a table within the paper.Peer reviewe

Laboratory spectroscopy of meteorite samples at UV-Vis-NIR wavelengths : Analysis and discrimination by principal components analysis

Meteorite samples are measured with the University of Helsinki integrating-sphere UV-vis-NIR spectrometer. The resulting spectra of 30 meteorites are compared with selected spectra from the NASA Planetary Data System meteorite spectra database. The spectral measurements are transformed with the principal component analysis, and it is shown that different meteorite types can be distinguished from the transformed data. The motivation is to improve the link between asteroid spectral observations and meteorite spectral measurements. (C) 2017 Elsevier Ltd. All rights reserved.Peer reviewe

Measuring the Terminal Heights of Bolides to Understand the Atmospheric Flight of Large Asteroidal Fragments

The extent of penetration into the Earth's atmosphere of a meteoroid is defined by the point where its kinetic energy is no longer sufficient to produce luminosity. For most of the cases this is the point where the meteoroid disintegrates in the atmosphere due to ablation process and dynamic pressure during flight. However, some of these bodies have particular physical properties (bigger size, higher bulk strength, etc.) or favorable flight conditions (lower entry velocity or/and a convenient trajectory slope, etc.) that allow them to become a meteorite-dropper and reach the ground. In both cases, we define the end of the luminous path of the trajectory as the terminal height or end height. Thus, the end point shows the amount of deceleration till the final braking. We thus assume that the ability of a fireball to produce meteorites is directly related to its terminal height. Previous studies have discussed the likely relationship between fireball atmospheric flight properties and the terminal height. Most of these studies require the knowledge of a set of properties and physical variables which cannot be determined with sufficient accuracy from ground-based observations. The recently validated dimensionless methodology offers a new approach to this problem. All the unknowns can be reduced to only two parameters which are easily derived from observations. Despite the calculation of the analytic solution of the equations of motion is not trivial, some simplifications are admitted. Here, we describe the best performance range and the errors associated with these simplifications. We discuss how terminal heights depend on two or three variables that are easily retrieved from the recordings, provided at least three trajectory (h, v) points. Additionally, we review the importance of terminal heights, and the way they have been estimated in previous studies. Finally we discuss a new approach for calculating terminal heights.Peer reviewe

Spectral modeling of meteorites at UV-vis-NIR wavelengths

We present a novel simulation framework for assessing the spectral properties of meteorite specimens. The framework utilizes a ray-optics code, which simulates light scattering by Gaussian-random-sphere particles large compared to the wavelength of the incident light and accounts for internal diffuse scatterers. The code uses incoherent input and computes phase matrices by utilizing incoherent scattering matrices. Reflectance spectra are modeled by introducing a combination of olivine, pyroxene, and iron, the most common materials present in meteorites that dominate their spectral features. The complex refractive indices of olivine and iron are obtained from existing databases. The refractive indices of pyroxene are derived using an optimization that utilizes our ray-optics code and the measured spectrum of the material. We demonstrate our approach by applying it on the measured meteorite reflectance spectra obtained with the University of Helsinki integrating-sphere UV-vis-NIR spectrometer. (C) 2017 Elsevier Ltd. All rights reserved.Peer reviewe

Photometric modelling for laboratory measurements of dark volcanic sand

We have performed laboratory measurements of the bidirectional reflectance factor (BRF) of a sample of dark volcanic sand. The measurements were carried out with three different treatments of the sample to produce different porosity and roughness characteristics. We model the measured BRF with a semi-numerical scattering model for particulate media, meant especially for dark planetary regoliths. We compare the BRF in two different spectral bands, 500-600 nm and 800-900 nm. The particulate medium (PM). scattering model is found to fit the measured data well, with a phase function representing the differences between the spectral bands. The interpretation of the physical parameters of the PM model is qualitatively sound, but remains somewhat uncertain due in part to the difficulty of characterizing the measured sample. (C) 2016 Elsevier Ltd. All rights reserved.Peer reviewe

Evolution of the dust trail of comet 17P/Holmes

Publisher Copyright: © 2022 The Author(s).The massive outburst of the comet 17P/Holmes in 2007 October is the largest known outburst by a comet thus far. We present a new comprehensive model describing the evolution of the dust trail produced in this phenomenon. The model comprises of multiparticle Monte Carlo simulation including the solar radiation pressure effects, gravitational disturbance caused by Venus, Earth and Moon, Mars, Jupiter and Saturn, and gravitational interaction of the dust particles with the parent comet itself. Good accuracy of computations is achieved by its implementation in Orekit, which executes Dormad-Prince numerical integration methods with higher precision. We demonstrate performance of the model by simulating particle populations with sizes from 0.001 to 1 mm with corresponding spherically symmetric ejection speed distribution, and towards the Sun outburst modelling. The model is supplemented with and validated against the observations of the dust trail in common nodes for 0.5 and 1 revolutions. In all cases, the predicted trail position showed a good match to the observations. Additionally, the hourglass pattern of the trail was observed for the first time within this work. By using variations of the outburst model in our simulations, we determine that the assumption of the spherical symmetry of the ejected particles leads to the scenario compatible with the observed hourglass pattern. Using these data, we make predictions for the two-revolution dust trail behaviour near the outburst point that should be detectable by using ground-based telescopes in 2022.Peer reviewe

Super-resolution photonic nanojet interferometry : photonic nanojet interaction with a polymer sample

Peer reviewe