Southwest Research Institute

MEGA-H is a multi-detector, wide-field telescope system that produces ultra-high-resolution, seamless images. The optical path employs pickoff mirrors that partition the image field onto three individual detectors. The detectors can be located conveniently apart from each other while preserving the whole FOV and producing a recombined image without any gaps. This architecture enables a scientist to choose the best detector for the task, which may have the good detection properties but insufficient number of pixels, and combine multiple detectors to achieve the desired pixel count. This camera system will initially be mounted behind a wide FOV white light imager and be capable of both wide FOV (10 degrees on diagonal) and high instantaneous field of view (iFOV) (

Stream interaction regions (SIRs) are formed where high-speed streams from coronal holes expand into slower preceding solar wind. Simulations have long shown significant latitudinal structuring to SIRs and their associated energetic populations, which have been additionally suggested from high-latitude Ulysses observations. However, multi-point observations of SIRs from observers at different latitudes are needed to constrain this variability. This includes better understanding the role of coronal hole properties and impacts of latitudinal variability in the preceding slow solar wind streams on the evolution of SIR structures. In this presentation, we focus on recent off-ecliptic Solar Orbiter observations in comparison with observations at ACE and STEREO-A to further explore the importance of latitudinal structuring of SIRs and associated energetic particles.

Auroral arcs in the high latitude are frequently observed during periods of northward interplanetary magnetic field (IMF). However, their generation mechanisms are not yet fully understood, due to the limited availability of simultaneous in-situ and optical auroral observations. In this talk, we present observations of recurrent tailward-propagating auroral arcs in the dawnside during a period of northward IMF. THEMIS satellites located near the dawnside magnetopause in the equatorial plane observed strong fluctuations in magnetic field and plasma parameters with periods of 5–7 minutes, suggesting the presence of surface waves or ULF waves. Subsequently, shorter-period fluctuations of 2-3 minutes were observed for an hour, which may indicate the development of Kelvin–Helmholtz instability (KHI). During these intervals, a ground-based all-sky imager detected recurrent auroral arcs detached from the poleward boundary of the auroral oval, with a period of 5–10 minutes, propagating predominantly tailward. DMSP observations revealed multiple auroral arcs on the dawnside, accompanied by electron precipitation associated with paired upward and downward field-aligned currents. Based on these coordinated space- and ground-based observations, we discuss several possible generation mechanisms for the observed auroral arcs, including surface waves, ULF waves, and KHI.

We report on new results analyzing Io’s upwelling thermal emission over the range of 0.6 to 22 GHz acquired with the Juno Microwave Radiometer (MWR) in December 2023 and February 2024. The microwave emission spectrum from the surface of Io is retrieved from the MWR calibrated brightness temperatures and represents the vertical temperature gradient in the upper 10s of meters of Io. A large spectral slope (>20K) is observed at all latitudes in the lowest frequency MWR channels suggesting significant endogenic near-surface heating. The spectral slope increases toward the north pole. We compare two end-member model fits to the MWR spectra; a conductive model and a model comprising cooling lava flows. The conductive model implies heat flows ranging from 1-3 W/m2. The alternative model of relatively fresh lava flows or heat vents covered by a cold, highly insulating crusts fits the MWR spectra with flows covering about 10% of the surface with a 3-8m thick crust. We show the regional distribution of sub-surface temperature anomalies with depth, comparing to previously catalogued hot spots, flow units and volcanic centers. We will discuss how model assumptions, such as the microwave loss tangent of the crust material and magma temperature, impact the results.

Magnetic reconnection at the near-Sun heliospheric current sheet (HCS) dissipates the Parker spiral and converts magnetic energy into kinetic energy of the plasma constituents. Observations at a radial distance of ~16.25 Rs by Parker Solar Probe associated with the encounter 14 (E14) HCS crossing have shown that reconnection-driven particle acceleration mechanisms, likely facilitated by the merging of large-scale flux tubes, are able to accelerate protons up to ~400 keV, which is ≈1000 times greater than the available magnetic energy per particle during this crossing (Desai et al. 2025; Phan et al. 2024). In this paper, we present a detailed analysis of the pitch-angle distributions, differential energy spectra, and maximum energies and spectra of protons and heavy ions (He, O, and Fe) in conjunction with observations of local wave activity during the E14 HCS crossing. Our results show the following: 1) First direct observations of the energization of protons and heavy ions during reconnection. 2) First direct observations that the power-law spectral slopes of heavy ions differ from that of protons, which contradicts previous simulation results where the spectral indices of all ion species are essentially identical. 3) First demonstration that the anisotropies and beams of ions produced during reconnection drive waves in the ion cyclotron range of frequencies. 4) First evidence that the pitch angle scattering of protons is stronger than that of the other ion species and that this might be responsible for the harder spectral slopes of the heavy ions compared with protons. In summary, PSP observations during the E14 HCS crossing provide strong evidence for in-situ reconnection-driven acceleration of protons and heavy ions at the near-Sun HCS that will need to be fully accounted for by contemporary reconnection-driven energization models.

Terrestrial planets—Mercury, Venus, Earth and Mars—formed by the accretion of smaller objects, each planet with their own timescale. The Earth was probably the latest terrestrial planet to form and reached about 99% of its final mass within about 60–100 Myr after condensation of the first solids in the Solar System. This contribution examines the disproportionate role of the last approximately 1% of Earth’s growth, or late accretion, in controlling its long-term interior evolution, and in particular metal-silicate mixing and bulk volatile budget. The coupling of impact and geodynamical simulations reveals underappreciated consequences of Earth’s late accretion with implications for a correct interpretation of the geochemical and geodynamical properties of the present Earth’s mantle. Similar implications are expected for Venus and Mars, and are also likely to occur and modulate the interior evolution of rocky exoplanets.

Jupiter’s moon Io is the most volcanically active body in the Solar System, powered by intense internal heating due to tidal dissipation. Although tidal friction is widely accepted as the main energy source, how this heat is distributed within Io and how it shapes the moon’s internal structure remain open questions. In this study, we use Io’s tidal response, quantified through the degree-2 Love number (k2), to constrain its interior, using recent estimates derived from Juno observations (Park et al., 2025).We model Io with a three-layer structure consisting of a fluid core, a viscoelastic mantle, and a crust, using an adapted version of the California Planetary Geophysics Code (CPGC). Tidal dissipation is self-consistently coupled to mantle rheology through an Andrade model, with viscosity and shear modulus updated as functions of the local melt fraction. We explore two end-member scenarios that differ in the treatment of the Andrade parameter β: in the first, β is held constant, representing a uniform dissipation regime dominated by deep-mantle heating; in the second, β varies with depth, allowing dissipation to be preferentially localized in the upper mantle. In both scenarios, viscosity and shear modulus evolve with melt fraction.Our results identify several partially molten mantle configurations whose real part of k2 is consistent with Juno constraints. In all acceptable models, melt fractions remain below the threshold required to form a global magma layer. To test the physical viability of these states, we compare thermodynamic melt production with the capacity for melt migration. We find that melt transport is efficient enough to prevent long-term melt accumulation, favoring a stable, partially molten “magma sponge” rather than a global magma ocean. These results provide new constraints on Io’s thermal state and are consistent with independent estimates of its global volcanic output.

Whistler-mode waves are a wave mode in plasma occurring near and below the electron cyclotron frequency. They are commonly observed in planetary magnetospheres and play a crucial role in accelerating and precipitating magnetospheric electrons. Using Juno’s observations, we investigate these waves in Jupiter’s magnetosphere, focusing on the region between 20 and 80 Jupiter radii on the post-midnight-to-dawn side. Observations from the Waves instrument show that these waves primarily occur in the lobes, where the magnetic field is strong and plasma density is low, rather than in the central magnetodisk, where the field is weaker and plasma is denser. Simultaneous electron measurements from JADE-E, combined with dispersion relation analysis, indicate that these waves are likely driven by a mono-directional electron population between ∼0.1 and 10 keV propagating anti-Jupiter-ward. Further controlled studies show that a local flux minimum at ∼0.3 keV in the electron energy spectrum, commonly observed during whistler-mode waves, is critical for wave growth. Based on their direction of motion, we suggest that these mono-directional electrons and the whistler-mode waves they generate are related to magnetosphere-ionosphere coupling. Our findings offer new insights into the interplay between whistler-mode waves and electrons in Jupiter’s magnetosphere.

We present observations of impulsive solar energetic particle events on 2025 March 20 observed at high heliolatitude by Solar Orbiter and compare them with near-ecliptic observations by the Wind spacecraft. Solar Orbiter, located at 0.38 au, a Carrington longitude of 139.7◦ and a latitude of −16.6◦, detected two ion events at ∼0.1-6 MeV and two electron events at ∼40-200 keV. These events exhibit clear velocity dispersion and strong field-aligned anisotropy. Velocity dispersion analysis of both ion and electron events yields path lengths consistent with the nominal Parker spiral length. Furthermore, the first electron event exhibits a double-power-law spectrum with an index of 2.3 ± 0.3 below a break energy of 58 ± 4 keV and an index of 4.0±0.2 at energies above, while the second electron event exhibits a single-power-law spectrum with an index of 4.6 ± 0.2. In contrast, the Wind spacecraft, located at 1 au, a Carrington longitude of 120.0◦, and a latitude of −7.1◦, observed only one electron event, which shows insignificant velocity dispersion and arrives ∼20 min later than expected. The Parker spiral footpoints of the two spacecraft were separated by ∼15◦ in longitude and ∼10◦ in latitude, providing a lower limit on the angular extent of impulsive electron events. The delayed arrival at Wind may be attributed to the electron diffusion in the solar source region.

Introduction Motivated by observed composition dependence in reconnection energy outflow and by theoretical and simulation studies predicting differences between heating of H+ and heavier ions, we investigated the ion composition dependence of heating associated with reconnection in 28 dayside magnetopause crossings in Magnetospheric Multiscale (MMS) data. Methods We applied Least Squares fitting to analyze the relationship of temperature change across the magnetopause exhaust to available magnetic energy. Available magnetic energy per ion-electron pair flowing into the magnetopause from the magnetosheath and magnetosphere ranged between a few tens of eV and ∼1750 eV. Results The individual fits for composition-nonspecific ions and for H+ were significantly lower than the empirical scaling relationship found previously between the temperature change and the inflowing magnetic energy; the fit for He++ was higher, with marginal significance. A composite data product combining H+ and He++ agreed with the empirical scaling relationship to within 95%. Discussion Although comparisons between heating of H+ and He++ are suggestive of enhanced heating of heavy ions, differences could not be identified conclusively due to high scatter and a small number of events with adequate densities of heavy ions.