arXiv subjects

S. A. Fuselier

Publications and source records attributed to S. A. Fuselier.

At least 19 recordsLinked to original sources

arXiv2026

Nitrogen- and nitrogen-oxygen-bearing organic molecules in comet 67P/Churyumov-Gerasimenko: An untargeted investigation

Comets provide a unique window into the history of the Solar System as they carry some of the best-preserved material and make it available to in situ exploration. A milestone in comet studies was the European Space Agency's Rosetta mission, which, for the first time, rendezvoused with a comet, namely 67P/Churyumov-Gerasimenko (67P), and studied it from a close range for two years. Amongst other unexpected insights, data from this mission show that comets contain a surprisingly large portion of organics, both in the refractory and the icy phases. For this work, we evaluated high-resolution mass spectra collected in comet 67P's inner coma by Rosetta's ROSINA-Double Focusing Mass Spectrometer (DFMS). In unprecedented detail, we investigated the N- and NO-bearing cometary complex organic molecules (COMs) of the general sum formula CnHmN and CnHmNO, where n and m are the stoichiometric coefficients of carbon and hydrogen. Our discussion-driven approach combines the empirical concept of Occam's razor with knowledge from studies of relevant astrophysical environments and constraints expected from naive bottom-up assembly of molecules. We present an exemplary minimal and non-unique set of molecules needed to explain the DFMS observations. While this set might not capture the full organic diversity, but rather its lower limit, it identifies many N- and NO-bearing COMs with reasonable certainty, while excluding others, potentially informing future observational campaigns, and hence contributes to the exploration of the origin and evolution of organic complexity in space. Among the key results is strong evidence for an abundant presence of heterocycles as well as substantial alkylation of both cyclic and acyclic species. These findings align well with reports on soluble organic matter in meteorites and asteroids and ...

astro-ph.EP↗

arXiv2026

Simultaneous TRACERS and THEMIS Observations of Reversed Cusp Ion Dispersions and Dual-Lobe Reconnection

We present observations from two consecutive TRACERS-2 orbits through the northern low-altitude cusp. During the first crossing, TRACERS-2 observed reversed cusp ion dispersion and sunward convection, consistent with magnetopause reconnection tailward of the cusp during this northward IMF interval. Simultaneous THEMIS-D observations at the equatorial magnetopause show heated magnetosheath plasma captured on closed field lines, with similar particle spectra as in in the low-altitude cusp, indicating that reconnection indeed occurred tailward of the cusp and in both hemispheres. When TRACERS-2 traversed the northern cusp again, 95 minutes later, the IMF was dominated by a negative BX component. Despite the different IMF conditions, TRACERS-2 recorded nearly the same cusp signatures as before, i.e., reversed ion dispersion and sunward convection. The observations indicate that tailward-of-cusp reconnection can occur for both northward and BX-dominated IMF and that these distinct IMF geometries can produce remarkably similar plasma and field signatures in the low-altitude cusp.

physics.space-ph↗

arXiv2025

Atomic and Molecular Nitrogen Ions at the Dayside Magnetopause During the 2024 Mother's Day Storm

Ion measurements made with the Hot Plasma Composition Analyzers of the Magnetospheric Multiscale Mission (MMS-HPCAs) during the Mother's Day Storm (Gannon Storm) of 10-13 May 2024 yield the first observations of atomic and molecular nitrogen ions in the Earth's dayside outer magnetosphere. A population of ions identified as doubly charged nitrogen and oxygen was also measured. These observations were made within a highly compressed magnetosphere at a geocentric distance of ~6 Earth Radii during the early recovery phase of the storm. From the ion composition measurements and accompanying magnetic field data, we determine the reconnection rate at the magnetopause; we compare this result to a model reconnection rate that assumes the presence of only atomic oxygen and hydrogen. The heavy ion-laden-mass density in the magnetosphere was greater than the shocked solar wind mass density in the magnetosheath. Despite these conditions, magnetic reconnection still occurred at the magnetopause.

physics.space-ph↗

arXiv2024

IBEX Observations of Elastic Scattering of Interstellar Helium by Solar Wind Particles

The IBEX-Lo instrument on the Interstellar Boundary Explorer (IBEX) mission observes primary and secondary interstellar helium in its 4 lowest energy steps. Observations of these helium populations have been systematically analyzed and compared to simulations using the analytic full integration of neutrals model (aFINM). A systematic difference is observed between the simulations and observations of secondary helium during solar cycle (SC) 24. We show that elastic scattering of primary helium by solar wind protons, which redistributes atoms from the core of the flux distribution, provides an explanation of the observed divergence from simulations. We verify that elastic scattering forms a halo in the wings of the primary He distribution in the spin-angle direction. Correcting the simulation for the effects of elastic scattering requires an increase of the estimated density of primary helium compared to previous estimates by Ulysses/GAS. Thus, based on our analysis of IBEX observations and $χ^2$ minimization of simulation data that include the effects of elastic scattering, any estimation of neutral interstellar helium density at 1 AU by direct detection of the peak flux of neutral helium needs to be adjusted by $~\sim$ 10%

astro-ph.SR↗

arXiv2024

Outstanding questions and future research of magnetic reconnection

This short article highlights the unsolved problems of magnetic reconnection in collisionless plasma. The advanced in-situ plasma measurements and simulations enabled scientists to gain a novel understanding of magnetic reconnection. Still, outstanding questions remain on the complex dynamics and structures in the diffusion region, on the cross-scale and regional couplings, on the onset of magnetic reconnection, and on the details of energetics. Future directions of the magnetic reconnection research in terms of new observations, new simulations and interdisciplinary approaches are discussed.

physics.plasm-ph↗

arXiv2024

Advanced methods for analyzing in-situ observations of magnetic reconnection

There is ample evidence for magnetic reconnection in the solar system, but it is a nontrivial task to visualize, to determine the proper approaches and frames to study, and in turn to elucidate the physical processes at work in reconnection regions from in-situ measurements of plasma particles and electromagnetic fields. Here an overview is given of a variety of single- and multi-spacecraft data analysis techniques that are key to revealing the context of in-situ observations of magnetic reconnection in space and for detecting and analyzing the diffusion regions where ions and/or electrons are demagnetized. We focus on recent advances in the era of the Magnetospheric Multiscale mission, which has made electron-scale, multi-point measurements of magnetic reconnection in and around Earth's magnetosphere.

physics.space-ph↗

arXiv2023

Ion Dynamics Across a Low Mach Number Bow Shock

A thorough understanding of collisionless shocks requires knowledge of how different ion species are accelerated across the shock. We investigate a bow shock crossing using the Magnetospheric Multiscale spacecraft after a coronal mass ejection crossed Earth, which led to solar wind consisting of protons, alpha particles, and singly charge helium ions. The low Mach number of the bow shock enabled the ions to be distinguished upstream and sometimes downstream of the shock. Some of the protons are specularly reflected and produce quasi-periodic fine structures in the velocity distribution functions downstream of the shock. Heavier ions are shown to transit the shock without reflection. However, the gyromotion of the heavier ions partially obscures the fine structure of proton distributions. Additionally, the calculated proton moments are unreliable when the different ion species are not distinguished by the particle detector. The need to high time-resolution mass-resolving ion detectors when investigating collisionless shocks is discussed.

physics.space-ph↗

arXiv2023

Oxygen-bearing organic molecules in comet 67P's dusty coma: first evidence for abundant heterocycles

The puzzling complexity of terrestrial biomolecules is driving the search for complex organic molecules in the Interstellar Medium (ISM) and serves as a motivation for many in situ studies of reservoirs of extraterrestrial organics from meteorites and interplanetary dust particles (IDPs) to comets and asteroids. Comet 67P/Churyumov-Gerasimenko (67P) -- the best-studied comet to date -- has been visited and accompanied for two years by the European Space Agency's Rosetta spacecraft. Around 67P's perihelion and under dusty conditions, the high-resolution mass spectrometer on board provided a spectacular glimpse into this comet's chemical complexity. For this work, we analyzed in unprecedented detail the O-bearing organic volatiles. In a comparison of 67P's inventory to molecules detected in the ISM, in other comets, and in Soluble Organic Matter (SOM) extracted from the Murchison meteorite, we also highlight the (pre)biotic relevance of different chemical groups of species. We report first evidence for abundant extraterrestrial O-bearing heterocycles (with abundances relative to methanol often on the order of 10% with a relative error margin of 30-50%) and various representatives of other molecule classes such as carboxylic acids and esters, aldehydes, ketones, and alcohols. Like with the pure hydrocarbons, some hydrogenated forms seem to be dominant over their dehydrogenated counterparts. An interesting example is tetrahydrofuran (THF) as it might be a more promising candidate for searches in the ISM than the long-sought furan itself. Our findings not only support and guide future efforts to investigate the origins of chemical complexity in space, but also they strongly encourage studies of, e.g., the ratios of unbranched vs. branched and hydrogenated vs. dehydrogenated species in astrophysical ice analogs in the laboratory as well as by modeling.

astro-ph.EP↗

arXiv2023

Interstellar Conditions Deduced from Interstellar Neutral Helium Observed by IBEX and Global Heliosphere Modeling

In situ observations of interstellar neutral (ISN) helium atoms by the IBEX-Lo instrument onboard the Interstellar Boundary Explorer (IBEX) mission are used to determine the velocity and temperature of the pristine very local interstellar medium (VLISM). Most ISN helium atoms penetrating the heliosphere, known as the primary population, originate in the pristine VLISM. As the primary atoms travel through the outer heliosheath, they charge exchange with He$^+$ ions in slowed and compressed plasma creating the secondary population. With more than 2.4 million ISN helium atoms sampled by IBEX during ISN seasons 2009-2020, we compare the observations with predictions of a parametrized model of ISN helium transport in the heliosphere. We account for the filtration of ISN helium atoms at the heliospheric boundaries by charge exchange and elastic collisions. We examine the sensitivity of the ISN helium fluxes to the interstellar conditions described by the pristine VLISM velocity, temperature, magnetic field, and composition. We show that comprehensive modeling of the filtration processes is critical for interpreting ISN helium observations, as the change in the derived VLISM conditions exceeds the statistical uncertainties when accounting for these effects. The pristine VLISM parameters found by this analysis are the flow speed (26.6 km s$^{-1}$), inflow direction in ecliptic coordinates (255.7$^\circ$, 5.04$^\circ$), temperature (7350 K), and B-V plane inclination to the ecliptic plane (53.7$^\circ$). The derived pristine VLISM He$^+$ density is $9.7\times10^3$ cm$^{-3}$. Additionally, we show a strong correlation between the interstellar plasma density and magnetic field strength deduced from these observations.

astro-ph.GA↗

arXiv2023

The Effect of Angular Scattering Imposed by Charge Exchange and Elastic Collisions on Interstellar Neutral Hydrogen Atoms

Angular scattering in charge exchange and elastic collisions between interstellar ions and neutral (ISN) atoms has been assumed to be negligible in previous studies. Here, we investigated the momentum transfer associated with the angular scattering of H atoms using Monte Carlo calculations to simulate their transport through the outer heliosheath. We considered two cases where charge exchange and elastic collisions between ISN H atoms and protons occur with and without momentum transfer in the outer heliosheath. We then simulated the transport of ISN H atoms inside the heliosphere to simulate count rates observed in the lowest energy bin of IBEX-Lo. We studied the effect of radiation pressure on the ISN H measurements for the cases with and without momentum transfer and compared them with our previous findings. We found an effective radiation parameter ($μ_{\scriptsize\textrm{eff}}$, which represents for force associated with radiation pressure relative to gravity) for the years 2009-2018 based on the longitudinal shift of the ISN H signal. The two cases with and without momentum transfer reproduce the longitudinal shift in accordance with variations in solar activity, in agreement with our previous results, and they result in similar values for the $μ_{\scriptsize\textrm{eff}}$, which is $\sim21-22 \%$ larger than the value found based on Ly$α$ observations.

physics.space-ph↗

arXiv2023

Relative In-flight Response of IBEX-Lo to Interstellar Neutral Helium Atoms

The IBEX-Lo instrument on the Interstellar Boundary Explorer (IBEX) mission measures interstellar neutral (ISN) helium atoms. The detection of helium atoms is made through negative hydrogen (H$^-$) ions sputtered by the helium atoms from the IBEX-Lo conversion surface. The energy spectrum of ions sputtered by ISN helium atoms is broad and overlaps the four lowest IBEX-Lo electrostatic analyzer (ESA) steps. Consequently, the energy response function for helium atoms does not correspond to the nominal energy step transmission. Moreover, laboratory calibration is incomplete because it is difficult to produce narrow-energy neutral atom beams that are expected for ISN helium atoms. Here, we analyze the ISN helium observations in ESA steps 1-4 to derive the relative in-flight response of IBEX-Lo to helium atoms. We compare the ratios of the observed count rates as a function of the mean ISN helium atom energy estimated using the Warsaw Test Particle Model (WTPM). The WTPM uses a global heliosphere model to calculate charge exchange gains and losses to estimate the secondary ISN helium population. We find that the modeled mean energies of ISN helium atoms, unlike their modeled fluxes, are not very sensitive to the very local interstellar medium parameters. The obtained relative responses supplement the laboratory calibration and enable more detailed quantitative studies of the ISN helium signal. A similar procedure that we applied to the IBEX-Lo observations may be used to complement laboratory calibration of the next-generation IMAP-Lo instrument on the Interstellar Mapping and Acceleration Probe (IMAP) mission.

physics.space-ph↗

arXiv2022

Abundant ammonium hydrosulphide embedded in cometary dust grains

Ammonium hydrosulphide has long since been postulated to exist at least in certain layers of the giant planets. Its radiation products may be the reason for the red colour seen on Jupiter. Several ammonium salts, the products of NH3 and an acid, have previously been detected at comet 67P/Churyumov-Gerasimenko. The acid H2S is the fifth most abundant molecule in the coma of 67P followed by NH3. In order to look for the salt NH4+SH-, we analysed in situ measurements from the Rosetta/ROSINA Double Focusing Mass Spectrometer during the Rosetta mission. NH3 and H2S appear to be independent of each other when sublimating directly from the nucleus. However, we observe a strong correlation between the two species during dust impacts, clearly pointing to the salt. We find that NH4+SH- is by far the most abundant salt, more abundant in the dust impacts than even water. We also find all previously detected ammonium salts and for the first time ammonium fluoride. The amount of ammonia and acids balance each other, confirming that ammonia is mostly in the form of salt embedded into dust grains. Allotropes S2 and S3 are strongly enhanced in the impacts, while H2S2 and its fragment HS2 are not detected, which is most probably the result of radiolysis of NH4+SH-. This makes a prestellar origin of the salt likely. Our findings may explain the apparent depletion of nitrogen in comets and maybe help to solve the riddle of the missing sulphur in star forming regions.

astro-ph.EP↗

arXiv2022

Ion Acceleration at Magnetotail Plasma Jets

We investigate a series of Earthward bursty bulk flows (BBFs) observed by the Magnetospheric Multiscale (MMS) spacecraft in Earth's magnetotail at (-24, 7, 4) RE in Geocentric Solar Magnetospheric (GSM) coordinates. At the leading edges of the BBFs, we observe complex magnetic field structures. In particular, we focus on one which presents a chain of small scale (~0.5 RE) dipolarizations, and another with a large scale (~3.5 RE) dipolarization. Although the two structures have different scales, both of these structures are associated with flux increases of supra-thermal ions with energies > 100 keV. We investigate the ion acceleration mechanism and its dependence on the mass and charge state. We show that the ions with gyroradii smaller than the scale of the structure are accelerated by the ion bulk flow. We show that whereas in the small scale structure, ions with gyroradii comparable with the scale of the structure undergo resonance acceleration, and the acceleration in the larger scale structure is more likely due to a spatially limited electric field.

physics.space-ph↗

arXiv2022

First comparison of composite 0.52-55 keV ENA spectra observed by IBEX and Cassini/INCA with simulated ENAs inferred by proton hybrid simulations downstream of the termination shock

We present a first comparison of Energetic Neutral Atom (ENA) heliosheath measurements, remotely sensed by the Interstellar Boundary Explorer (IBEX) mission and the Ion and Neutral Camera (INCA) on the Cassini mission, with modeled ENA inferred from interstellar pickup protons that have been accelerated at the termination shock, using hybrid simulations. The observed ENA intensities are an average value over the time period from 2009 to the end of 2012, along the Voyager 2 trajectory. The hybrid simulations parameters for the solar wind, interstellar pickup ions (PUIs), and magnetic field upstream of the termination shock, where Voyager 2 crossed, are based on observations. We report an energy dependent discrepancy between observed and simulated ENA fluxes, with the observed ENA fluxes, being consistently higher than the simulated ones, and discuss possible causes of this discrepancy.

physics.space-ph↗

arXiv2022

Very Local Interstellar Medium Revealed by Complete Solar Cycle of Interstellar Neutral Helium Observations with IBEX

The IBEX-Lo instrument on board the Interstellar Boundary Explorer (IBEX) mission samples interstellar neutral (ISN) helium atoms penetrating the heliosphere from the very local interstellar medium (VLISM). In this study, we analyze the IBEX-Lo ISN helium observations covering a complete solar cycle, from 2009 through 2020 using a comprehensive uncertainty analysis including statistical and systematic sources.W e employ the Warsaw Test Particle Model to simulate ISN helium fluxes at IBEX, which are subsequently compared with the observed count rate in the three lowest energy steps of IBEX-Lo. The $χ^2$ analysis shows that the ISN helium flows from ecliptic $(λ,β)=(255.59^{\circ}\pm0.23^{\circ}, 5.14^{\circ}\pm0.08^{\circ})$, with speed $v_\text{HP}=25.86\pm0.21$ km s$^{-1}$ and temperature $T_\text{HP}=7450\pm140$ K at the heliopause. Accounting for gravitational attraction and elastic collisions, the ISN helium speed and temperature in the pristine VLISM far from the heliopause are $v_\text{VLISM}=25.9$ km s$^{-1}$ and $T_\text{VLISM}=6150$ K, respectively. The time evolution of the ISN helium fluxes at 1 au over 12 years suggests significant changes in the IBEX-Lo detection efficiency, higher ionization rates of ISN helium atoms in the heliosphere than assumed in the model, or an additional unaccounted signal source in the analyzed observations. Nevertheless, we do not find any indication of the evolution of the derived parameters of ISN helium over the period analyzed. Finally, we argue that the continued operation of IBEX-Lo to overlap with the Interstellar Mapping and Acceleration Probe (IMAP) will be pivotal in tracking possible physical changes in the VLISM.

physics.space-ph↗

arXiv2021

The structure of a perturbed magnetic reconnection electron diffusion region

We report in situ observations of an electron diffusion region (EDR) and adjacent separatrix region. We observe significant magnetic field oscillations near the lower hybrid frequency which propagate perpendicularly to the reconnection plane. We also find that the strong electron-scale gradients close to the EDR exhibit significant oscillations at a similar frequency. Such oscillations are not expected for a crossing of a steady 2D EDR, and can be explained by a complex motion of the reconnection plane induced by current sheet kinking propagating in the out-of-reconnection-plane direction. Thus all three spatial dimensions have to be taken into account to explain the observed perturbed EDR crossing.

physics.plasm-ph↗

arXiv2021

Cyanogen, cyanoacetylene, and acetonitrile in comet 67P and their relationship to the cyano radical

The cyano radical (CN) is one of the most frequently remotely observed species in space, also in comets. Data from the high-resolution Double Focusing Mass Spectrometer (DFMS) on board the Rosetta orbiter, collected in the inner coma of comet 67P/Churyumov-Gerasimenko, revealed an unexpected chemical complexity, and, recently, also more CN than expected from photodissociation of its most likely parent hydrogen cyanide (HCN). This work is dedicated to the derivation of abundances relative to HCN of three cometary nitriles (including structural isomers) from DFMS data. Mass spectrometry of complex mixtures does not always allow distinction of structural isomers. We assumed the most stable and most abundant (in similar environments) structure in our analysis, that is HCN for CHN, CH3CN for C2H3N, HC3N for C3HN, and NCCN for C2N2. For cyanoacetylene (HC3N) and acetonitrile (CH3CN) the complete mission timeline was evaluated, while cyanogen (NCCN) often was below detection limit. By carefully selecting periods where cyanogen was above detection limit, we were able to follow the abundance ratio between NCCN and HCN from 3.16 au inbound to 3.42 au outbound. These are the first measurements of NCCN in a comet.We find that neither NCCN, nor any of the other two nitriles, is sufficiently abundant to be a relevant alternative parent to CN.

astro-ph.EP↗

arXiv2020

Molecule dependent oxygen isotopic ratios in the coma of comet 67P/Churyumov-Gerasimenko

The ratios of the three stable oxygen isotopes 16O, 17O and 18O on Earth and, as far as we know in the solar system, show variations on the order of a few percent at most, with a few outliers in meteorites. However, in the interstellar medium there are some highly fractionated oxygen isotopic ratios in some specific molecules. The goal of this work is to investigate the oxygen isotopic ratios in different volatile molecules found in the coma of comet 67P/Churyumov-Gerasimenko and compare them with findings from interstellar clouds in order to assess commonalities and differences. To accomplish this goal, we analyzed data from the ROSINA instrument on Rosetta during its mission around the comet. 16O/18O ratios could be determined for O2, methanol, formaldehyde, carbonyl sulfide and sulfur monoxide/dioxide. For O2 the 16O/17O ratio is also available. Some ratios are strongly enriched in the heavy isotopes, especially for sulfur bearing molecules and formaldehyde, whereas for methanol the ratios are compatible with the ones in the solar system. O2 falls in-between, but its oxygen isotopic ratios clearly differ from water, which likely rules out an origin of O2 from water, be it by radiolysis, dismutation during sublimation or the Eley-Rideal process from water ions hitting the nucleus as postulated in the literature.

astro-ph.EP↗