arXiv subjects

Jamey R. Szalay

Publications and source records attributed to Jamey R. Szalay.

12 recordsLinked to original sources

arXiv2026

Local Interstellar Flow Parameters from the First Intersection of IMAP-Lo's Parameter Tubes

The Sun's motion through the interstellar medium creates a flow of interstellar neutral (ISN) atoms through the heliosphere. ISN He, due to its high universal abundance and relatively low ionization rate, is the most abundant of the interstellar species near 1 au and ideal for flow parameter determination. The Interstellar Boundary Explorer (IBEX) measurements of ISN He flow parameters (speed, temperature, and direction) yielded a tube in 4D parameter space -- narrow in cross-section but highly extended along one parameter axis (e.g., ecliptic longitude direction). This ``4D parameter tube'' results in large systematic uncertainties, a direct consequence of IBEX-Lo's fixed viewing orientation on the spacecraft. On the Interstellar Mapping and Acceleration Probe (IMAP), the articulation of the IMAP-Lo boresight using its pivot platform enables multiple viewing orientations of the ISN flow for significant systematic uncertainty reduction. We provide first results that definitively intersect ISN parameter tubes for elongation angles $79^\circ$, 94$^\circ$, and 109$^\circ$, resulting in precise interstellar parameters: speed $26.37 \pm 0.82$ km s$^{-1}$, ecliptic longitude direction $74.85^\circ \pm 0.96^\circ$, ecliptic latitude direction $-5.212^\circ \pm 0.035^\circ$, and temperature $7740^{+770}_{-730}$ K. The inferred flow of the Very Local Interstellar Medium is not consistent with either the Local Interstellar Cloud or the G-Cloud, but rather an intermediate state. IMAP is now positioned to study the detailed physics of this complex, nearby interstellar region. By resolving and understanding its physics, we determine how the heliosphere responds to the local interstellar flow, and how it may evolve in time

astro-ph.GA↗

arXiv2026

Constraining Electron-Impact Ionization of O$_2$ Through UV Aurora Observations at Ganymede

While photoionization rates of Ganymede's O$_2$ dominated atmosphere are well constrained, the contribution of electron-impact ionization is rather uncertain. Previous quantitative estimates have relied on assumptions about densities and energy distributions of precipitating electrons, or on rare spacecraft measurements that cannot be unambiguously mapped to the regions of ionization. In this study, we present a novel approach to quantify electron-impact ionization rates directly through OI 1356 Å emission brightness observations. The analysis of measured cross sections reveals that the ionization-to-excitation ratio is limited to 10-60 over all electron energies, reducing the uncertainty of estimating ionization rates to a factor less than 6. We apply this method to Juno UVS observations of Ganymede's aurora. We find that the OI 1356 Å brightness of the auroral ovals is well described by 3-5° latitude wide Gaussian distributions centered on the open-closed field line boundary, with an average peak of 120 R. The average brightness outside the ovals in the polar and equatorial background regions is ~8 R. From these observations, we derive a global map of electron-impact ionization rates, which are at least an order of magnitude higher than photoionization rates. The estimated total global ionization rate is 1.3-7.6$\times$10$^{26}$ s$^{-1}$, with average column rates of ~5$\times$10$^{9}$ cm$^{-2}$s$^{-1}$ in the ovals and ~3$\times$10$^{8}$ cm$^{-2}$s$^{-1}$ in the background regions. Comparison of radio occultation measurements with predicted electron densities indicates that transport processes are the dominant loss mechanism in Ganymede's ionosphere. The rate of ionospheric outflow of O$_2^+$ is 0.1-2$\times$10$^{26}$ s$^{-1}$ or 0.5-11 kg s$^{-1}$, indicating 0.03-0.5 cm Myr$^{-1}$ erosion of Ganymede's surface ice.

astro-ph.EP↗

arXiv2025

A Comparison of Geminid Models with the PSP/WISPR-observed Phaethon Dust Trail

White-light observations from the WISPR instrument on NASA's Parker Solar Probe recently revealed the presence of a narrow, dense dust trail close to the orbit of asteroid 3200 Phaethon. Although Geminid-related, it aligns imperfectly with Phaethon's orbit and known Geminid meteoroid orbits. To address the nature of this dust trail, we performed a detailed comparison between the WISPR trail observations and several well-developed Geminid models. Simulating these models in the WISPR field of view visually demonstrates that the WISPR trail almost certainly represents the true ``density core'' of the Geminid stream. Trends in model trail width and offset from Phaethon's orbit, both as functions of true anomaly, agree with observations to varying extents. All the models, however, place their apparent core interior to the parent orbit due to Poynting-Robertson forces, contradictory to the WISPR trail which is exterior to Phaethon's orbit. Therefore, Phaethon's current orbit likely does not represent the orbit of the system parent, which most probably had a larger semi-major axis. These findings provide new initial conditions for future Geminid models, with WISPR identifying the Geminid core's position.

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arXiv2025

A Rotational Disruption Crisis for Zodiacal Dust

A systematic torque from anisotropic radiation can rapidly spin up irregular grains to the point of breakup. We apply the standard theory of rotational disruption from radiative torques to solar system grains, finding that grains with radii $\sim$0.03 --3 $μ$m at 1 a.u. from the Sun are spun to the point of breakup on timescales $\lesssim1$ yr even when assuming them to have an unrealistically high tensile strength of pure meteoritic iron. Such a rapid disruption timescale is incompatible with both the abundance of micron-sized grains detected in the inner solar system and with the low production rate of $β$ meteoroids. We suggest the possibility that zodiacal grains have a strong propensity to attain rotational equilibrium at low angular velocity (a so-called low-$J$ attractor) and that the efficacy of rotational disruption in the Solar System -- and likely elsewhere -- has been greatly overestimated.

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arXiv2024

How long-lived grains dominate the shape of the Zodiacal Cloud

Grain-grain collisions shape the 3-dimensional size and velocity distribution of the inner Zodiacal Cloud and the impact rates of dust on inner planets, yet they remain the least understood sink of zodiacal dust grains. For the first time, we combine the collisional grooming method combined with a dynamical meteoroid model of Jupiter-family comets (JFCs) that covers four orders of magnitude in particle diameter to investigate the consequences of grain-grain collisions in the inner Zodiacal Cloud. We compare this model to a suite of observational constraints from meteor radars, the Infrared Astronomical Satellite (IRAS), mass fluxes at Earth, and inner solar probes, and use it to derive the population and collisional strength parameters for the JFC dust cloud. We derive a critical specific energy of $Q^*_D=5\times10^5 \pm 4\times10^5 R_\mathrm{met}^{-0.24}$ J kg$^{-1}$ for particles from Jupiter-family comet particles, making them 2-3 orders of magnitude more resistant to collisions than previously assumed. We find that the differential power law size index $-4.2\pm0.1$ for particles generated by JFCs provides a good match to observed data. Our model provides a good match to the mass production rates derived from the Parker Solar Probe observations and their scaling with the heliocentric distance. The higher resistance to collisions of dust particles might have strong implications to models of collisions in solar and exo-solar dust clouds. The migration via Poynting-Roberson drag might be more important for denser clouds, the mass production rates of astrophysical debris disks might be overestimated, and the mass of the source populations might be underestimated. Our models and code are freely available online.

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arXiv2023

Formation, Structure, and Detectability of the Geminids Meteoroid Stream

The Geminids meteoroid stream produces one of the most intense meteor showers at Earth. It is an unusual stream in that its parent body is understood to be an asteroid, (3200) Phaethon, unlike most streams which are formed via ongoing cometary activity. Until recently, our primary understanding of this stream came from Earth-based measurements of the Geminids meteor shower. However, the Parker Solar Probe (PSP) spacecraft has transited near the core of the stream close to its perihelion and provides a new platform to better understand this unique stream. Here, we create a dynamical model of the Geminids meteoroid stream, calibrate its total density to Earth-based measurements, and compare this model to recent observations of the dust environment near the Sun by PSP. For the formation mechanisms considered, we find the core of the meteoroid stream predominantly lies interior to its parent body orbit and expect grains in the stream to be $\gtrsim$10 $μ$m in radius. Data-model comparisons of the location of the stream relative to Phaethon's orbit are more consistent with a catastrophic formation scenario, in contrast to cometary formation. Finally, while PSP transits very near the core of the stream, the impact rate expected by Geminids meteoroids is orders of magnitude below the impact rates observed by PSP, and hence undetectable in-situ. We similarly expect the upcoming DESTINY+ mission to be unable to detect appreciable quantities of Geminids grains far from (3200) Phaethon.

astro-ph.EP↗

arXiv2023

The Io, Europa and Ganymede auroral footprints at Jupiter in the ultraviolet: positions and equatorial lead angles

Jupiter's satellite auroral footprints are a consequence of the interaction between the Jovian magnetic field with co-rotating iogenic plasma and the Galilean moons. The disturbances created near the moons propagate as Alfvén waves along the magnetic field lines. The position of the moons is therefore "Alfvénically" connected to their respective auroral footprint. The angular separation from the instantaneous magnetic footprint can be estimated by the so-called lead angle. That lead angle varies periodically as a function of orbital longitude, since the time for the Alfvén waves to reach the Jovian ionosphere varies accordingly. Using spectral images of the Main Alfvén Wing auroral spots collected by Juno-UVS during the first forty-three orbits, this work provides the first empirical model of the Io, Europa and Ganymede equatorial lead angles for the northern and southern hemispheres. Alfvén travel times between the three innermost Galilean moons to Jupiter's northern and southern hemispheres are estimated from the lead angle measurements. We also demonstrate the accuracy of the mapping from the Juno magnetic field reference model (JRM33) at the completion of the prime mission for M-shells extending to at least 15RJ . Finally, we shows how the added knowledge of the lead angle can improve the interpretation of the moon-induced decametric emissions.

astro-ph.EP↗

arXiv2023

Probing Ganymede's atmosphere with HST Ly$α$ images in transit of Jupiter

We report results from far-ultraviolet observations by the Hubble Space Telescope of Jupiter's largest moon Ganymede transiting across the planet's dayside hemisphere. {Within} a targeted campaign on 9 September 2021 two exposures were taken during one transit passage to probe for attenuation of Jupiter's hydrogen Lyman-$α$ dayglow above the moon limb. The background dayglow is slightly attenuated over an extended region around Ganymede, with stronger attenuation in the second exposure when Ganymede was near the planet's center. In the first exposure when the moon was closer to Jupiter's limb, the effects from the Ganymede corona are hardly detectable, likely because the Jovian Lyman-$α$ dayglow is spectrally broader and less intense at this viewing geometry. The obtained vertical H column densities of around $(1-2)\times 10^{12}$~cm$^{-2}$ are consistent with previous results. Constraining angular variability around Ganymede's disk, we derive an upper limit on a local H$_2$O column density of $(2-3)\times 10^{16}$~cm$^{-2}$, such as could arise from outgassing plumes in regions near the observed moon limb.

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arXiv2022

Continued PSP/WISPR Observations of a Phaethon-related Dust Trail

We present an update to the first white-light detections of a dust trail observed closely following the orbit of asteroid (3200) Phaethon, as seen by the Wide-field Imager for Parker Solar Probe (WISPR) instrument on the NASA Parker Solar Probe (PSP) mission. Here we provide a summary and analysis of observations of the dust trail over nine separate mission encounters between October 2018 and August 2021 that saw the spacecraft approach to within 0.0277 au of the orbit of Phaethon. We find the photometric and estimated dust mass properties to be inline with those in the initial publication, with a visual (V) magnitude of approximately 16.1$\pm$0.3 per pixel, corresponding to a surface brightness of 26.1 mag arcsec$^{-2}$, and an estimated mass of dust within the range $10^{10}$ kg - $10^{12}$ kg depending on the assumed dust properties. However, the key finding of this survey is the discovery that the dust trail does not perfectly follow the orbit of Phaethon, with a clear separation noted between them that increases as a function of true anomaly, though the trail may differ from Phaethon's orbit by as little as 1-degree in periapsis.

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arXiv2022

Modeling Meteoroid Impacts on the Juno spacecraft

Events which meet certain criteria from star tracker images onboard the Juno spacecraft have been proposed to be due to interplanetary dust particle impacts on its solar arrays. These events have been suggested to be caused by particles with diameters larger than 10 micrometers. Here, we compare the reported event rates to expected dust impact rates using dynamical meteoroid models for the four most abundant meteoroid/dust populations in the inner solar system. We find that the dust impact rates predicted by dynamical meteoroid models are not compatible with either the Juno observations in terms of the number of star tracker events per day, or with the variations of dust flux on Juno's solar panels with time and position in the solar system. For example, the rate of star tracker events on Juno's anti-sunward surfaces is the largest during a period during which Juno is expected to experience the peak impact fluxes on the opposite, sunward hemisphere. We also investigate the hypothesis of dust leaving the Martian Hill sphere originating either from the surface of Mars itself or from one of its moons. We do not find such a hypothetical source to be able to reproduce the star tracker event rate variations observed by Juno. We conclude that the star tracker events observed by Juno are unlikely to be the result of instantaneous impacts from the Zodiacal Cloud.

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arXiv2020

Lunar Volatiles and Solar System Science

Understanding the origin and evolution of the lunar volatile system is not only compelling lunar science, but also fundamental Solar System science. This white paper (submitted to the US National Academies' Decadal Survey in Planetary Science and Astrobiology 2023-2032) summarizes recent advances in our understanding of lunar volatiles, identifies outstanding questions for the next decade, and discusses key steps required to address these questions.

astro-ph.IM↗

arXiv2019

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

Given the compositional diversity of asteroids, and their distribution in space, it is impossible to consider returning samples from each one to establish their origin. However, the velocity and molecular composition of primary minerals, hydrated silicates, and organic materials can be determined by in situ dust detector instruments. Such instruments could sample the cloud of micrometer-scale particles shed by asteroids to provide direct links to known meteorite groups without returning the samples to terrestrial laboratories. We extend models of the measured lunar dust cloud from LADEE to show that the abundance of detectable impact-generated microsamples around asteroids is a function of the parent body radius, heliocentric distance, flyby distance, and speed. We use monte carlo modeling to show that several tens to hundreds of particles, if randomly ejected and detected during a flyby, would be a sufficient number to classify the parent body as an ordinary chondrite, basaltic achondrite, or other class of meteorite. Encountering and measuring microsamples shed from near-earth and main-belt asteroids, coupled with complementary imaging and multispectral measurements, could accomplish a thorough characterization of small, airless bodies.

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