Authors:A.G.G.M. Tielens Abstract: Astronomical observations and analysis of stardust isolated from meteorites have revealed a highly diverse interstellar and circumstellar grain inventory, including a wide range of amorphous materials and crystalline compounds (silicates and carbon). This diversity reflects the wide range of stellar sources injecting solids into the interstellar medium each with its own physical characteristics such as density, temperature and elemental composition and highlights the importance of kinetics rather than thermodynamics in the formation of these compounds. Based upon the extensive literature on soot formation in terrestrial settings, detailed kinetic pathways have been identified for the formation of carbon dust in C-rich stellar ejecta. These have been incorporated in astronomical models for these environments. In recent years, the chemical routes in the nucleation of oxides and silicates have been the focus of much astronomical research. These aspects of stardust formation will be reviewed and “lessons” for dust formation in planetary atmospheres will be drawn with the emphasis on the influence of kinetics on the characteristics and structure of dust in these environments. PubDate: 2022-05-27T09:09:20Z
Authors:L. J. Warden, C. L. Waters, M. D. Sciffer, M. Vellante Abstract: This paper presents a comparison of three methods to estimate the latitudinal resonance width of field line resonant, ultra-low frequency waves detected at the ground. These are a spatial domain, full-width half-maximum method and frequency domain amplitude-phase and amplitude-division methods. These methods were used to estimate the resonance width of several field line resonant intervals occurring on 26 November 2001, 1 October 2012, and 19 June 2015. The 19 June 2015 interval used data from one low, two mid, and one high latitudes. It was found that the resonance width estimates were different for each method and with how the data were processed. The most suitable methods and data processing were determined from a damped driven harmonic oscillator model. The amplitude-division methods yielded the most accurate results when the ground magnetic field data were processed with a boxcar window function or a frequency domain, exponential smoothing taper. The amplitude-phase method tended to underestimate the resonance width. The full-width half-maximum method gave accurate results for a high spatial resolution linear piece-wise curve fitted to the spectral amplitude with latitude profile. An accurate estimate of the latitudinal resonance width requires a correct choice of data processing, estimate method, resonance profile with latitude, and resonance model. PubDate: 2022-05-26T00:00:00Z
Authors:Victor A. Pinto, Amy M. Keesee, Michael Coughlan, Raman Mukundan, Jeremiah W. Johnson, Chigomezyo M. Ngwira, Hyunju K. Connor Abstract: Forecasting ground magnetic field perturbations has been a long-standing goal of the space weather community. The availability of ground magnetic field data and its potential to be used in geomagnetically induced current studies, such as risk assessment, have resulted in several forecasting efforts over the past few decades. One particular community effort was the Geospace Environment Modeling (GEM) challenge of ground magnetic field perturbations that evaluated the predictive capacity of several empirical and first principles models at both mid- and high-latitudes in order to choose an operative model. In this work, we use three different deep learning models-a feed-forward neural network, a long short-term memory recurrent network and a convolutional neural network-to forecast the horizontal component of the ground magnetic field rate of change (dBH/dt) over 6 different ground magnetometer stations and to compare as directly as possible with the original GEM challenge. We find that, in general, the models are able to perform at similar levels to those obtained in the original challenge, although the performance depends heavily on the particular storm being evaluated. We then discuss the limitations of such a comparison on the basis that the original challenge was not designed with machine learning algorithms in mind. PubDate: 2022-05-25T00:00:00Z
Authors:Jiro Shimoda Abstract: We review recent investigations of the statistical nature of turbulent magnetic fields in supernova remnants. After a brief presentation of the role of the magnetic field in the cosmic-ray acceleration and synchrotron emissions from the accelerated electrons, we introduce previous investigations about the turbulent magnetic field in the supernova remnants. Then we describe the new method to analyze the statistical nature of the fields and introduce observational results reported on. Finally, we also discuss about the origin of the turbulent magnetic field and future prospects of observational studies of cosmic-ray acceleration in the supernova remnants. PubDate: 2022-05-23T00:00:00Z
Authors:J. M. da Silva Santos, S. M. White, K. Reardon, G. Cauzzi, S. Gunár, P. Heinzel, J. Leenaarts Abstract: Quiescent filaments appear as absorption features on the solar disk when observed in chromospheric lines and at continuum wavelengths in the millimeter (mm) range. Active region (AR) filaments are their small-scale, low-altitude analogues, but they could not be resolved in previous mm observations. This spectral diagnostic can provide insight into the details of the formation and physical properties of their fine threads, which are still not fully understood. Here, we shed light on the thermal structure of an AR filament using high-resolution brightness temperature (Tb) maps taken with ALMA Band 6 complemented by simultaneous IRIS near-UV spectra, Hinode/SOT photospheric magnetograms, and SDO/AIA extreme-UV images. Some of the dark threads visible in the AIA 304 Å passband and in the core of Mg ii resonance lines have dark (Tb PubDate: 2022-05-23T00:00:00Z
Authors:Yu Sun, Yiliang Li, Chaoqun Zhang, Xiaorong Qin, Jianxun Shen, Hongping He, Yongxin Pan Abstract: Chlorite is the second-most common class of clay minerals on the Martian surface and has been found to coexist with illite in some regions. Although previous studies have paid much attention to the formation of this assemblage, the post-depositional evolution cannot be neglected because the aqueous activities may alter the mineral assemblage and distribution. Here, we report on the post-depositional weathering of lacustrine-fluvial deposits collected from yardangs and dune-covering lake beds in the western Qaidam Basin, one of the largest and highest terrestrial Mars analogs. Mineralogical analysis shows that Fe-clinochlore and illite are the main clay components deposited as detrital particles. Electron microscopic observations of small rusty concretions from yardang deposits revealed that iron was released from clinochlore and formed ferrihydrite in fractures. We suggest that the activities of ephemeral waters after the deposition provide the major source of water that influences the migration of Fe in a long-lasting hyperarid climate. A similar iron-releasing mechanism could have occurred in Nili Fossae on Mars because multiple aqueous activities have shaped the terrains where chlorite illite deposits were identified by orbital near-infrared reflectance spectroscopy. Thus, reconstruction of the aqueous history of ancient Mars from surface minerals requires consideration of post-depositional processes, since groundwater/meteoric water may continuously interact with clay mineral-bearing deposits on Mars after their formation. PubDate: 2022-05-23T00:00:00Z
Authors:Kiley L. Yeakel, Jon D. Vandegriff, Tadhg M. Garton, Caitriona M. Jackman, George Clark, Sarah K. Vines, Andrew W. Smith, Peter Kollmann Abstract: Several machine learning algorithms and feature subsets from a variety of particle and magnetic field instruments on-board the Cassini spacecraft were explored for their utility in classifying orbit segments as magnetosphere, magnetosheath or solar wind. Using a list of manually detected magnetopause and bow shock crossings from mission scientists, random forest (RF), support vector machine (SVM), logistic regression (LR) and recurrent neural network long short-term memory (RNN LSTM) classification algorithms were trained and tested. A detailed error analysis revealed a RNN LSTM model provided the best overall performance with a 93.1% accuracy on the unseen test set and MCC score of 0.88 when utilizing 60 min of magnetometer data ( B , Bθ, Bϕ and BR) to predict the region at the final time step. RF models using a combination of magnetometer and particle data, spanning H+, He+, He++ and electrons at a single time step, provided a nearly equivalent performance with a test set accuracy of 91.4% and MCC score of 0.84. Derived boundary crossings from each model’s region predictions revealed that the RNN model was able to successfully detect 82.1% of labeled magnetopause crossings and 91.2% of labeled bow shock crossings, while the RF model using magnetometer and particle data detected 82.4 and 74.3%, respectively. PubDate: 2022-05-20T00:00:00Z
Authors:Douglas Rowland, Michael Collier, John Keller, Robert Pfaff, Jeffrey Klenzing, Jason McLain, James Clemmons, James Hecht Abstract: The VISualizing Ion Outflow via Neutral atom imaging during a Substorm (VISIONS) sounding rocket mission investigated the factors leading to ion outflow following a geomagnetic substorm. In situ and remote sensing instrumentation provided complementary measurements that have been combined to yield an in-depth look at the phenomena associated with ion outflow. In particular, the inclusion of instrumentation that provided high spatial and temporal resolution “images” of low-energy neutral atom (ENA) emissions from the nightside auroral zone following a substorm has led to new insights. The observed ENAs were spatially structured, and strongly associated with regions of intense 630.0 nm auroral emissions. The ENAs in the auroral zone were predominantly up-going, consistent with thick-target scattering in the region where the ENA mean free path is close to or less than the atmospheric scale height. PubDate: 2022-05-19T00:00:00Z
Authors:Anna Mittelholz, Catherine L. Johnson Abstract: Mars’ crustal magnetic field holds information on the planet’s interior evolution and exterior processes that have modified the crust. Crustal magnetization records an ancient dynamo field that indicates very different interior conditions in the past, possibly linked to the presence of a thicker early atmosphere. Current data sets have provided a wealth of information on the ancient magnetic field, and on the acquisition and modification of magnetization in the crust. However, many puzzles remain regarding the nature and origin of crustal magnetization, and the timing and characteristics of the past dynamo. Here we use recent advances in understanding martian magnetism to highlight open questions, and ways in which they can be addressed through laboratory analysis, modeling and new data sets. Many of the outstanding key issues require data sets that close the gap in spatial resolution between available global satellite and local surface magnetic field measurements. Future missions such as a helicopter, balloon or airplane can provide areal high resolution coverage of the magnetic field, vital to major advances in understanding planetary crustal magnetic fields. PubDate: 2022-05-19T00:00:00Z
Authors:H. George, A. Osmane, E. K. J. Kilpua, S. Lejosne , L. Turc, M. Grandin, M. M. H. Kalliokoski, S. Hoilijoki, U. Ganse, M. Alho, M. Battarbee, M. Bussov, M. Dubart, A. Johlander, T. Manglayev, K. Papadakis, Y. Pfau-Kempf, J. Suni, V. Tarvus, H. Zhou, M. Palmroth Abstract: Radial diffusion coefficients quantify non-adiabatic transport of energetic particles by electromagnetic field fluctuations in planetary radiation belts. Theoretically, radial diffusion occurs for an ensemble of particles that experience irreversible violation of their third adiabatic invariant, which is equivalent to a change in their Roederer L* parameter. Thus, the Roederer L* coordinate is the fundamental quantity from which radial diffusion coefficients can be computed. In this study, we present a methodology to calculate the Lagrangian derivative of L* from global magnetospheric simulations, and test it with an application to Vlasiator, a hybrid-Vlasov model of near-Earth space. We use a Hamiltonian formalism for particles confined to closed drift shells with conserved first and second adiabatic invariants to compute changes in the guiding center drift paths due to electric and magnetic field fluctuations. We investigate the feasibility of this methodology by computing the time derivative of L* for an equatorial ultrarelativistic electron population travelling along four guiding center drift paths in the outer radiation belt during a 5 minute portion of a Vlasiator simulation. Radial diffusion in this simulation is primarily driven by ultralow frequency waves in the Pc3 range (10–45 s period range) that are generated in the foreshock and transmitted through the magnetopause to the outer radiation belt environment. Our results show that an alternative methodology to compute detailed radial diffusion transport is now available and could form the basis for comparison studies between numerical and observational measurements of radial transport in the Earth’s radiation belts. PubDate: 2022-05-18T00:00:00Z
Authors:Dan Winske, Lynn B. Wilson Abstract: We discuss Peter Gary’s contributions to the understanding of the origin and properties of ultra-low frequency (ULF) waves in the Earth’s foreshock during the period when the International Sun Earth Explorer spacecraft (ISEE-1 and -2) provided unique data about the plasma and wave environment in this region. Peter’s work concerning the linear theory of electromagnetic ion beam instabilities is contained in five journal articles and then summarized in a review article, all of which are discussed here. Brief summaries of observations and theory prior to ISEE as well as to later work are also included. PubDate: 2022-05-16T00:00:00Z
Authors:Robin Ciardullo Abstract: One of the great surprises of the late 1980s was the discovery that the [O III] λ5007 planetary nebula luminosity function (PNLF) could be used as a precision extragalactic standard candle. Despite the lack of any robust theory for the phenomenon, the technique passed a myriad of internal and external tests, and became an extremely reliable tool for obtaining distances to large galaxies within ∼20 Mpc. But in more recent years, the use of the technique has declined, due in part to the changing landscape of cosmology. Here we review the history of the PNLF, the experiments that confirmed its utility, and the reasons why interest in the method faded at the turn of the millennium. We also describe how and why the PNLF is making a comeback, and present some of the method’s recent results. Finally, we discuss how the PNLF must be analyzed in the era of precision cosmology, and detail the issues that must be overcome in order to address the current tension between local measures of the Hubble constant and values derived from the microwave background. If these issues can be understood, then the PNLF can provide a useful cross-check on distance measurements out to ∼40 Mpc. PubDate: 2022-05-16T00:00:00Z
Authors:Martin Ferus, Antonín Knížek, Lukáš Petera, Adam Pastorek, Jana Hrnčířová, Luboš Jankovič, Ondřej Ivanek, Jiří Šponer, Anna Křivková, Homa Saeidfirozeh, Svatopluk Civiš, Elias Chatzitheodoridis, Klaudia Mráziková, Lukáš Nejdl, Franz Saija, Judit E. Šponer, Giuseppe Cassone Abstract: Influx of matter from impacting meteoroids and hydrothermal crater weathering are important factors modifying the rock and mineral inventory of young planets undergoing heavy bombardment. These processes may have influenced not only the geochemical environment of, e.g., early Mars and other planets, but also the peculiar prebiotic chemistry on early Earth. Here, we present a synergistic experimental and computational investigation of the intermediates of chemical reactions of the formamide-based synthesis of canonical and non-canonical nucleobases by thermochemistry in hot hydrothermal crater environments. We put our findings into context with previously investigated plasma-initiated synthesis occuring directly during impact. Both processes result into the formation of all canonical nucleobases, hypoxanthine, purine, and into the onset of the simplest amino acid glycine. Furthermore, it turns out that radical species such as CN and H play a key role in the plasma-assisted impact chemistry. However, post-impact thermochemistry is essential for the origin of formamidine and 2-aminoacetonitrile, intermediate species detected in this study by means of FTIR spectroscopy. PubDate: 2022-05-13T00:00:00Z
Authors:Y.-M. Wang Abstract: Although wanting to become an astronomer from an early age, I ended up in solar physics purely by chance, after first working in high-energy astrophysics. I’ve never regretted switching from the pulsar to the solar magnetosphere, because solar physics has a great advantage over other areas of astrophysics—in the enormous amount of high-quality data available, much of it underutilized. I’ve often wondered why theoreticians and modelers don’t spent more time looking at these data (perhaps they feel that it is cheating, like taking a peek at the answers to a difficult homework assignment'). Conversely, I wonder why observers and data analysts aren’t more skeptical of the theoretical models—especially the fashionable ones. PubDate: 2022-05-12T00:00:00Z
Authors:Devin Huyghebaert, Matthias Clahsen, Jorge L. Chau, Toralf Renkwitz, Ralph Latteck, Magnar G. Johnsen, Juha Vierinen Abstract: Multiple propagation modes between different bistatic radar links were measured during the operations of a very high frequency (VHF) 32.55 MHz radar system in northern Norway. The Spread Spectrum Interferometric Multistatic meteor radar Observing Network (SIMONe) Norway system detected meteor trails, direct transmitter to receiver signal propagation, over-the-horizon signal propagation from the SIMONe Germany system, ground and/or sea scatter, and ionospheric scatter on 27 August 2021 between 16:30–20:00 UT. These simultaneous detections were during an active ionospheric period with multiple occurrences of energetic charged particle precipitation. The SIMONe systems used continuous-wave (CW) pseudo-random phase modulated transmit signals and interferometry to make it possible to isolate each of these propagation modes and examine their characteristics. Different multistatic links at three receiver locations were analyzed, providing multistatic measurements of the regions with spatial and temporal resolutions on the order of 1.5 km and 2 s. The analysis techniques are described, with characteristics of the radar signal presented for each propagation mode and multistatic link. This study serves to highlight the capabilities of the SIMONe Norway system to research multiple aspects of ionospheric phenomena, specifically in the lower thermosphere-mesosphere boundary region. PubDate: 2022-05-10T00:00:00Z
Authors:Hannah R. Kerner, Umaa Rebbapragada, Kiri L. Wagstaff, Steven Lu, Bryce Dubayah, Eric Huff, Jake Lee, Vinay Raman, Sakshum Kulshrestha Abstract: Automatic detection of outliers is universally needed when working with scientific datasets, e.g., for cleaning datasets or flagging novel samples to guide instrument acquisition or scientific analysis. We present Domain-agnostic Outlier Ranking Algorithms (DORA), a configurable pipeline that facilitates application and evaluation of outlier detection methods in a variety of domains. DORA allows users to configure experiments by specifying the location of their dataset(s), the input data type, feature extraction methods, and which algorithms should be applied. DORA supports image, raster, time series, or feature vector input data types and outlier detection methods that include Isolation Forest, DEMUD, PCA, RX detector, Local RX, negative sampling, and probabilistic autoencoder. Each algorithm assigns an outlier score to each data sample. DORA provides results interpretation modules to help users process the results, including sorting samples by outlier score, evaluating the fraction of known outliers in n selections, clustering groups of similar outliers together, and web visualization. We demonstrated how DORA facilitates application, evaluation, and interpretation of outlier detection methods by performing experiments for three real-world datasets from Earth science, planetary science, and astrophysics, as well as one benchmark dataset (MNIST/Fashion-MNIST). We found that no single algorithm performed best across all datasets, underscoring the need for a tool that enables comparison of multiple algorithms. PubDate: 2022-05-10T00:00:00Z
Authors:Laurence Sabin, Jesús A. Toalá, Gerardo Ramos-Larios, Martín A. Guerrero Abstract: Similar to other classes of astronomical objects, there is a large discrepancy between the total count of theoretically predicted planetary nebulae (PNe) and the number of those actually observed. This discrepancy introduces bias in our attempt to globally understand and characterize the PNe population. Major efforts have been made to find the missing PNe. In particular, the INT Photometric Hα Survey (IPHAS) has, since its debut, provided a whelm of new (candidate) PNe, some of which have been studied in depth using various methodologies such as deep imaging and low- and high-resolution spectroscopy. Here, we present the outcome of the analysis of a first group of these well-investigated IPHAS PNe with a focus on the extended ones. We show that, in general, the missing objects that were expected to be unveiled by the survey (low density, evolved, and distant) are indeed discovered, but the survey also allows the retrieval of “simply” overlooked PNe. PubDate: 2022-05-10T00:00:00Z
Authors:Robert J. Leamon, Scott W. McIntosh, Alan M. Title Abstract: The Sun’s variability is controlled by the progression and interaction of the magnetized systems that form the 22-year magnetic activity cycle (the “Hale Cycle”) as they march from their origin at ∼55° latitude to the equator, over ∼19 years. We will discuss the end point of that progression, dubbed “terminator” events, and our means of diagnosing them. In this paper we expand on the Extended Solar Cycle framework to construct a new solar activity “clock” which maps all solar magnetic activity onto a single normalized epoch based on the terminations of Hale Magnetic Cycles. Defining phase 0*2π on this clock as the Terminators, then solar polar field reversals occur at ∼ 0.2*2π, and the geomagnetically quiet intervals centered around solar minimum start at ∼ 0.6*2π and end at the terminator, thus lasting 40% of the cycle length. At this onset of quiescence, dubbed a “pre-terminator,” the Sun shows a radical reduction in active region complexity and, like the terminator events, is associated with the time when the solar radio flux crosses F10.7 = 90 sfu. We use the terminator-based clock to illustrate a range of phenomena that further emphasize the strong interaction of the global-scale magnetic systems of the Hale Cycle: the vast majority, 96%, of all X-flares happen between the Terminator and pre-Terminator. In addition to the X-rays from violent flares, rapid changes in the number of energetic photons—EUV spectral emission from a hot corona and the F10.7 solar radio flux—impinging on the atmosphere are predictable from the Terminator-normalized unit cycle, which has implications for improving the fidelity of atmospheric modelling. PubDate: 2022-05-10T00:00:00Z
Authors:Harald Yndestad Abstract: This study utilizes time-series data devised to measure solar irradiation, sea surface temperatures, and temperatures in the lower atmosphere to gain a better understanding of how gravitational effects from the moon and Jovian planets (Jupiter, Saturn, Uranus, and Neptune) influence solar activity and climatic conditions on Earth. Then, standard statistical methods are used to determine the degree of correlation among these time series and construct a Jovian gravitational model. The study reveals a direct relationship between JSUN perihelion coincidences and TSI amplitude variations in cycles up to 4,450 years. The forced solar accumulation of heat in oceans introduces a new phase relation between solar forced cycles and new climate variation. Earth’s axis nutation cycles have coincidences with lunar nodal tide cycles and lunar forced sea surface temperature cycle periods up to 446 years. Earth’s temperature variation shows coincidence with constructive and destructive interference between lunar-forced and accumulated solar-forced temperature variations in oceans. Upcoming events have a computed modern temperature maximum in 2025 and a deep minimum in 2070. Interference between solar-forced temperature cycles of 333,2142, and 4,450 years and a lunar-forced temperature cycle of 445 years indicates that “The Little Ice Age” covers a total period of 820 years from 1330 to 2150 A.D. and an upcoming temporary cold climate period from 2070 to 2150. PubDate: 2022-05-10T00:00:00Z
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