Astronomy Research Works
Permanent URI for this collectionhttp://hdl.handle.net/1903/1587
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Item Animated Sequences Showing the Ejecta Produced in the DART Impact of Asteroid (65803) Didymos(2025-01-17) Farnham, TonyThis data collection contains animated sequences showing different aspects of the ejecta that were observed after the Double Asteroid Impact Test (DART) spacecraft crashed into Dimorphos, the moon of asteroid (65803) Didymos on September 26, 2022. The images comprising the sequences were obtained with the LICIACube Unit Key Explorer (LUKE) instrument on board the LICIACube spacecraft that flew by the Didymos system about 3 minutes after the impact event. Although the sequences are comprised of the same observations they are presented in different ways to emphasize various aspects of the ejecta field. These animations are intended as a supplement to the individual LUKE images, to provide insight and to help in the interpretation of the data in support of studies that address spatial and temporal changes in the DART ejecta field. Note that in some of the sequences, black sections may encroach in from the sides. These are gaps in the data where the asteroids moved to the edge of the camera's detector.Item Measurements of boulders ejected in the Double Asteroid Redirection Test (DART) impact(2025-01-17) Farnham, TonyThis data collection contains tables that provide measurements of the positions and brightnesses of meter-sized boulders that were ejected when the Double Asteroid Impact Test (DART) spacecraft crashed into Dimorphos, the moon of asteroid (65803) Didymos on September 26, 2022. The measurements come from the LICIACube Unit Key Explorer (LUKE) instrument on board the LICIACube spacecraft that flew by the Didymos system about 3 minutes after the impact event. The positions table provides the pixel locations of each boulder in the images where it was detected, while the photometry table gives the brightness for each boulder in each of the images where it was measured.Item Code and Data for 'Generalized Time-Series Analysis for In-Situ Spacecraft Observations: Anomaly Detection and Data Prioritization using Principal Components Analysis and Unsupervised Clustering'(2024) Finley, Matthew G.; Martinez-Ledesma, Miguel; Paterson, William R.; Argall, Matthew R.; Miles, David M.; Dorelli, John C.; Zesta, EftyhiaItem Dynamics of the Storm Time Magnetopause and Magnetosheath Boundary Layers: An MMS-THEMIS Conjunction(Wiley, 2024-02-13) Rice, Rachel C.; Chen, Li-Jen; Gershman, Dan; Fuselier, Stephen A.; Burkholder, Brandon L.; Gurram, Harsha; Beedle, Jason; Shuster, Jason; Petrinec, Steven M.; Pollock, Craig; Cohen, Ian; Gabrielse, Christine; Escoubet, Philippe; Burch, JamesThis letter uses simultaneous observations from Magnetosphere Multiscale (MMS) and Time History of Events and Macroscale Interactions during Substorms (THEMIS) to address the dynamics of the magnetopause and magnetosheath boundary layers during the main phase of a storm during which the interplanetary magnetic field (IMF) reverses from south to north. Near the dawn terminator, MMS observes two boundary layers comprising open and closed field lines and containing energetic electrons and ring current oxygen. Some closed field line regions exhibit sunward convection, presenting an avenue to replenish dayside magnetic flux lost during the storm. Meanwhile, THEMIS observes two boundary layers in the pre-noon sector which strongly resemble those observed at the flank by MMS. Observations from the three THEMIS spacecraft indicate the boundary layers are still evolving several hours after the IMF has turned northward. These observations advance our knowledge of the dynamic magnetopause and magnetosheath boundary layers under the combined effects of an ongoing storm and changing IMF.Item Surprising Decrease in the Martian He Bulge During PEDE-2018 and Changes in Upper Atmospheric Circulation(Wiley, 2023-07-12) Elrod, Meredith K.; Bougher, Stephen; Roeten, Kali; Arnold, KennethUsing the Neutral Gas and Ion Mass Spectrometer (NGIMS) on the Mars Atmosphere Volatile and Evolution spacecraft (MAVEN), we analyzed data from Mars Year (MY) 32, 34, and 35 to examine the He bulge during the northern winter solstice (Ls ∼ 180–240), specifically focusing on the effects from the planet encircling dust event (PEDE-2018). He collects on the dawn/nightside winter polar hemisphere of Mars. The seasonal migration of the He bulge has been observed and modeled (M. Elrod et al., 2017, https://doi.org/10.1002/2016JA023482; Gupta et al., 2021, https://doi.org/10.1029/2021JE006976). The MAVEN orbit precesses around Mars allowing for a variety of latitude and local time observations throughout the Martian year. MY 32, 34, and 35 had the best possible opportunities to observe the He bulge during northern winter (Ls ∼ 180–240). NGIMS observations during MY 32 and MY 35 revealed a He bulge from the nightside to dawn in alignment with modeling and previous publications. However, in MY 34, during the PEDE, the He bulge was not present, indicating that the PEDE directly impacted upper atmospheric circulation. Updates in modeling indicate changes in circulation and winds can cause He to shift further north than MAVEN was able to observe. While adding a simple static version of gravity waves to the Mars Global Ionosphere Thermosphere Model model may account for some of the variations in the global circulation during the dust event, other studies (e.g., Yiğit, 2023, https://doi.org/10.1038/s41561-022-01118-7) have posited that the gravity waves during the dust storm were more variable than the initial parameters we have included.Item Orbital Characterization of the Composition and Distribution of Spinels Across the Crisium Region: Insight From Luna 20 Samples(Wiley, 2023-04-28) Moriarty, D. P. III; Simon, S. B.; Shearer, C. K.; Haggerty, S. E.; Petro, N.; Li, ShuaiSpinels represent a small fraction of lunar surface materials but provide important insights into the petrological evolution of the lunar crust and mantle. Previous remote sensing analyses of highlands spinel-bearing lithologies have focused on pure Mg-Al spinels, which are rare in the lunar sample collection. Using Moon Mineralogy Mapper data, we develop and test an approach for detecting spectral signatures of spinel across a wider range of Mg, Al, Fe, Cr, Ti-bearing compositions than have been addressed in previous studies, including within mafic-bearing assemblages. This approach is validated through integration with laboratory-measured spinel spectra and petrographic observations of samples returned by the Luna 20 mission from the Hilly and Furrowed Terrain surrounding the Crisium Basin. Applying this approach to data from the Crisium region, small abundances of spinel (<∼5 vol%) with a range of Mg, Al, Fe, Cr, and Ti content and petrologic origin (inferred from Luna 20 samples) were found to be widespread within highlands soils across the Crisium region. This result diverges from previous remote sensing analyses, which only reported small, isolated exposures of pure Mg-Al spinel (as well as a possible detection of Fe, Cr-bearing spinels localized within pyroclastic materials at Sinus Aestuum). Geologic associations of candidate spinel detections across this region are consistent with a shallow crustal origin rather than excavation from depth during the Crisium-forming impact. These spinels are detectible in near-infrared spectroscopic data, particularly in areas of low optical maturity and may influence the spectral continuum of highlands soils.Item Soft X-Ray Imaging of Earth's Dayside Magnetosheath and Cusps Using Hybrid Simulations(Wiley, 2023-05-11) Ng, J.; Walsh, B.M.; Chen, L.-J.; Omelchenko, Y.Interactions between solar wind ions and neutral hydrogen atoms in Earth's exosphere can lead to the emission of soft X-rays. Upcoming missions such as SMILE and LEXI aim to use soft X-ray imaging to study the global structure of the magnetosphere. Although the magnetosheath and dayside magnetopause can often be driven by kinetic physics, it has typically been omitted from fluid simulations used to predict X-ray emissions. We study the possible results of soft X-ray imaging using hybrid simulations under quasi-radial interplanetary magnetic fields, where ion-ion instabilities drive ultra-low frequency foreshock waves, leading to turbulence in the magnetosheath, affecting the dynamics of the cusp and magnetopause. We simulate soft X-ray emission to determine what may be seen by missions such as LEXI, and evaluate the possibility of identifying kinetic structures. While kinetic structures are visible in high-cadence imaging, current instruments may not have the time resolution to discern kinetic signals.Item Temporal, Spatial, and Velocity-Space Variations of Electron Phase Space Density Measurements at the Magnetopause(Wiley, 2023-03-21) Shuster, J. R.; Gershman, D. J.; Giles, B. L.; Bessho, N.; Sharma, A. S.; Dorelli, J. C.; Uritsky, V.; Schwartz, S. J.; Cassak, P. A.; Denton, R. E.; Chen, L.-J.; Gurram, H.; Ng, J.; Burch, J.; Webster, J.; Torbert, R.; Paterson, W. R.; Schiff, C.; Viñas, A. F.; Avanov, L. A.; Stawarz, J.; Li, T. C.; Liu, Y.-H.; Argall, M. R.; Afshari, A.; Payne, D. S.; Farrugia, C.J.; Verniero, J.; Wilder, F.; Genestreti, K.; da Silva, D. E.Temporal, spatial, and velocity-space variations of electron phase space density are measured observationally and compared for the first time using the four magnetospheric multiscale (MMS) spacecraft at Earth's magnetopause. Equipped with these unprecedented spatiotemporal measurements offered by the MMS tetrahedron, we compute each term of the electron Vlasov equation that governs the evolution of collisionless plasmas found throughout the universe. We demonstrate how to use single spacecraft measurements to improve the resolution of the electron pressure gradient that supports nonideal parallel electric fields, and we develop a model to intuit the types of kinetic velocity-space signatures that are observed in the Vlasov equation terms. Furthermore, we discuss how the gradient in velocity-space sheds light on plasma energy conversion mechanisms and wave-particle interactions that occur in fundamental physical processes such as magnetic reconnection and turbulence.Item Hybrid Simulations of the Cusp and Dayside Magnetosheath Dynamics Under Quasi-Radial Interplanetary Magnetic Fields(Wiley, 2022-10-17) Ng, J.; Chen, L.-J.; Omelchenko, Y.; Zou, Y.; Lavraud, B.Under quasi-radial interplanetary magnetic fields (IMF), foreshock turbulence can have an impact on the magnetosheath and cusps depending on the location of the quasi-parallel shock. We perform three-dimensional simulations of Earth's dayside magnetosphere using the hybrid code HYPERS, and compare northward and southward quasi-radial IMF configurations. We study the magnetic field configuration, fluctuations in the magnetosheath and the plasma in the regions around the northern cusp. Under northward IMF with Earthward Bx, there is a time-varying plasma depletion layer immediately outside the northern cusp. In the southward IMF case, the impact of foreshock turbulence and high-speed jets, together with magnetopause reconnection, can lead to strong density enhancements in the cusp.Item Whistler Waves Associated With Electron Beams in Magnetopause Reconnection Diffusion Regions(Wiley, 2022-09-12) Wang, Shan; Bessho, Naoki; Graham, Daniel B.; Le Contel, Olivier; Wilder, Frederick D.; Khotyaintsev, Yuri V.; Genestreti, Kevin J.; Lavraud, Benoit; Choi, Seung; Burch, James L.Whistler waves are often observed in magnetopause reconnection associated with electron beams. We analyze seven MMS crossings surrounding the electron diffusion region (EDR) to study the role of electron beams in whistler excitation. Waves have two major types: (a) Narrow-band waves with high ellipticities and (b) broad-band waves that are more electrostatic with significant variations in ellipticities and wave normal angles. While both types of waves are associated with electron beams, the key difference is the anisotropy of the background population, with perpendicular and parallel anisotropies, respectively. The linear instability analysis suggests that the first type of wave is mainly due to the background anisotropy, with the beam contributing additional cyclotron resonance to enhance the wave growth. The second type of broadband waves are excited via Landau resonance, and as seen in one event, the beam anisotropy induces an additional cyclotron mode. The results are supported by particle-in-cell simulations. We infer that the first type occurs downstream of the central EDR, where background electrons experience Betatron acceleration to form the perpendicular anisotropy; the second type occurs in the central EDR of guide field reconnection. A parametric study is conducted with linear instability analysis. A beam anisotropy alone of above ∼3 likely excites the cyclotron mode waves. Large beam drifts cause Doppler shifts and may lead to left-hand polarizations in the ion frame. Future studies are needed to determine whether the observation covers a broader parameter regime and to understand the competition between whistler and other instabilities.
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