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H$_2$O$_2$ is part of Europa's water-ice radiolytic cycle and a potential source of oxidants to Europa's subsurface ocean. However, factors controlling the concentration of this critical surface species remain unclear. Though laboratory experiments suggest that Europa's H$_2$O$_2$ should be concentrated in the coldest, most ice-rich regions toward the poles, Keck adaptive optics observations have shown the strongest H$_2$O$_2$ signatures in comparatively warm, salt-bearing terrain at low latitudes. As a result, it was suggested that the local non-ice composition of these terrains -- particularly hypothesized enrichments of CO$_2$ -- may be a more dominant control on H$_2$O$_2$ than temperature or water-ice abundance. Here, we use observations of Europa from the NASA Infrared Telescope Facility, Keck Observatory, and JWST to disentangle the potential effects of temperature and composition. In order to isolate the effect of temperature on Europa's H$_2$O$_2$, we use the ground-based observations to assess its response to temperature changes over timescales associated with Europa's daily eclipse and diurnal cycle. We use JWST Cycle 1 data to look for any geographic correlation between Europa's H$_2$O$_2$ and CO$_2$. Both changes in Europa's 3.5-$\mu$m H$_2$O$_2$ absorption band from pre to post eclipse and across a local day suggest minimal effects of the local temperature on these timescales. In contrast, the JWST observations show a strong positive correlation between Europa's H$_2$O$_2$ and CO$_2$ bands, supporting the previously suggested possibility that the presence of CO$_2$ in the ice may enhance H$_2$O$_2$ concentrations via electron-scavenging., Comment: 17 pages, 4 figures, Accepted to the Planetary Science Journal

An important testable prediction of dynamical instability models for the early evolution of the Solar System is that Jupiter Trojans share a source population with the Kuiper belt. Concrete evidence of this prediction remains elusive, as Kuiper belt objects (KBOs) and Jupiter Trojans appear to have different surface compositions. We address the long-standing question of Trojan origin by finding a dynamical sub-population in the Kuiper belt with Trojan-like colors. Combining existing photometric data with our own surveys on Keck I and Palomar P200, we find that the low-perihelion ($q<30 $AU, $a>30 $AU) component of the Kuiper belt has colors that bifurcate similarly to the Jupiter Trojans, unlike Centaurs ($a<30 $AU) which have redder, Kuiper belt-like colors. To connect the Jupiter Trojans to the Kuiper belt, we test whether the distinct Trojan-like colors of low-perihelion KBOs result from surface processing, or are sourced from a specific population in the Kuiper belt. By simulating the evolution of the Canada-France Ecliptic Plane Survey synthetic population of KBOs for four billion years, we find that differences in heating timescales cannot result in a significant depletion of Very Red low-perihelion KBOs as compared to the Centaurs. We find that the neutrally-colored scattered disk objects ($e>0.6$ KBOs) contribute more to the low-perihelion KBO population rather than Centaurs, resulting in their different colors., Comment: 17 pages, 7 figures, Accepted to PSJ

We examine high spatial resolution Galileo/NIMS observations of the young (~1 My - 20 My) impact features, Pwyll and Manann\'{a}n craters, on Europa's trailing hemisphere in an effort to constrain irradiation timescales. We characterize their composition using a linear spectral modeling analysis and find that both craters and their ejecta are depleted in hydrated sulfuric acid relative to nearby older terrain. This suggests that the radiolytic sulfur cycle has not yet had enough time to build up an equilibrium concentration of H2SO4, and places a strong lower limit of the age of the craters on the equilibrium timescale of the radiolytic sulfur cycle on Europa's trailing hemisphere. Additionally, we find that the dark and red material seen in the craters and proximal ejecta of Pwyll and Manann\'{a}n show the spectroscopic signature of hydrated, presumably endogenic salts. This suggests that the irradiation-induced darkening and redenning of endogenic salts thought to occur on Europa's trailing hemisphere has already happened at Pwyll and Manann\'{a}n, thereby placing an upper limit on the timescale by which salts are irradiation reddened., Comment: 13 pages, 6 figures

The solar system's distant reaches exhibit a wealth of anomalous dynamical structure, hinting at the presence of a yet-undetected, massive trans-Neptunian body - Planet 9. Previous analyses have shown how orbital evolution induced by this object can explain the origins of a broad assortment of exotic orbits, ranging from those characterized by high perihelia to those with extreme inclinations. In this work, we shift the focus toward a more conventional class of TNOs, and consider the observed census of long-period, nearly planar, Neptune-crossing objects as a hitherto-unexplored probe of the Planet 9 hypothesis. To this end, we carry out comprehensive $N-$body simulations that self-consistently model gravitational perturbations from all giant planets, the Galactic tide, as well as passing stars, stemming from initial conditions that account for the primordial giant planet migration and sun's early evolution within a star cluster. Accounting for observational biases, our results reveal that the orbital architecture of this group of objects aligns closely with the predictions of the P9-inclusive model. In stark contrast, the P9-free scenario is statistically rejected at a $\sim5\,\sigma$ confidence-level. Accordingly, this work introduces a new line of evidence supporting the existence of Planet 9 and further delineates a series of observational predictions poised for near-term resolution., Comment: 11 pages, 5 figures, accepted for publication in The Astrophysical Journal Letters

We use 1.4-4.6 micron multi-band photometry of the small inner Uranian and Neptunian satellites obtained with the James Webb Space Telescope's near-infrared imager NIRCam to characterize their surface compositions. We find that the satellites of the ice giants have, to first-order, similar compositions to one another, with a 3.0 micron absorption feature possibly associated with an O-H stretch, indicative of water ice or hydrated minerals. Additionally, the spectrophotometry for the small ice giant satellites matches spectra of some Neptune Trojans and excited Kuiper belt objects, suggesting shared properties. Future spectroscopy of these small satellites is necessary to identify and better constrain their specific surface compositions., Comment: 14 pages, 5 figures, Accepted to the Planetary Science Journal

We present a search for Planet Nine using the second data release of the Pan-STARRS1survey. We rule out the existence of a Planet Nine with the characteristics of that predicted in Brown & Batygin (2021) to a 50% completion depth of $V=21.5$. This survey, along with previous analyses of the Zwicky Transient Facility (ZTF) and Dark EnergySurvey (DES) data, rules out 78% of the Brown \& Batygin parameter space. Much of the remaining parameter space is at $V>21$ in regions near and in the area where the northern galactic plane crosses the ecliptic., Comment: AJ, in press

We present observations obtained with the Near Infrared Spectrograph on JWST of the five Jupiter Trojans that will be visited by the Lucy spacecraft -- the Patroclus-Menoetius binary, Eurybates, Orus, Leucus, and Polymele. The measured 1.7-5.3 $\mu$m reflectance spectra, which provide increased wavelength coverage, spatial resolution, and signal-to-noise ratio over previous ground-based spectroscopy, reveal several distinct absorption features. We detect a broad OH band centered at 3 $\mu$m that is most prominent on the less-red objects Eurybates, Patroclus-Menoetius, and Polymele. An additional absorption feature at 3.3-3.6 $\mu$m, indicative of aliphatic organics, is systematically deeper on the red objects Orus and Leucus. The collisional fragment Eurybates is unique in displaying an absorption band at 4.25 $\mu$m that we attribute to bound or trapped CO$_2$. Comparisons with other solar system small bodies reveal broad similarities in the 2.7-3.6 $\mu$m bands with analogous features on Centaurs, Kuiper belt objects (KBOs), and the active asteroid 238P. In the context of recent solar system evolution models, which posit that the Trojans initially formed in the outer solar system, the significant attenuation of the 2.7-3.6 $\mu$m absorption features on Trojans relative to KBOs may be the result of secondary thermal processing of the Trojans' surfaces at the higher temperatures of the Jupiter region. The CO$_2$ band manifested on the surface of Eurybates suggests that CO$_2$ may be a major constituent in the bulk composition of Trojans, but resides in the subsurface or deeper interior and is largely obscured by refractory material that formed from the thermophysical processes that were activated during their inward migration., Comment: Published in PSJ. 13 pages, 6 figures

Jupiter's moon Europa has a subsurface ocean, the chemistry of which is largely unknown. Carbon dioxide (CO$_2$) has previously been detected on the surface of Europa, but it was not possible to determine whether it originated from subsurface ocean chemistry, was delivered by impacts, or was produced on the surface by radiation processing of impact-delivered material. We map the distribution of CO$_2$ on Europa using observations obtained with the James Webb Space Telescope (JWST) and find a concentration of CO$_2$ within Tara Regio, a recently resurfaced terrain. This indicates the CO$_2$ is derived from an internal carbon source. We propose the CO$_2$ formed in the internal ocean, though we cannot rule out formation on the surface by radiolytic conversion of ocean-derived organics or carbonates., Comment: This is the author's version of the work. It is posted here by permission of the AAAS for personal use, not for redistribution. The definitive version was published in Science on September 21, 2023, DOI: https://doi.org/10.1126/science.adg4155

A weak absorption feature at 2.07 \textmu m on Europa's trailing hemisphere has been suggested to arise from radiolytic processing of an endogenic salt, possibly sourced from the interior ocean. However, if the genesis of this feature requires endogenic material to be present, one might expect to find a correlation between its spatial distribution and the recently disrupted chaos terrains. Using archived near-infrared observations from Very Large Telescope/SINFONI with a $\sim$1 nm spectral resolution and a linear spatial resolution $\sim$130 km, we examine the spatial distribution of this feature in an effort to explore this endogenic formation hypothesis. We find that while the presence of the 2.07 \textmu m feature is strongly associated with the irradiation pattern on Europa's trailing hemisphere, there is no apparent association between the presence or depth of the absorption feature and Europa's large-scale chaos terrain. This spatial distribution suggests that the formation pathway of the 2.07 \textmu m feature on Europa is independent of any endogenous salts within the recent geology. Instead, we propose that the source of this feature may simply be a product of the radiolytic sulfur cycle or arise from some unidentified parallel irradiation process. Notably, the 2.07 \textmu m absorption band is absent from the Pwyll crater ejecta blanket, suggesting that radiolytic processing has not had enough time to form the species responsible and placing a lower limit on the irradiation timescale. We are unable to find a plausible spectral match to the 2.07 \textmu m feature within the available laboratory data., Comment: 12 pages, 3 figures, published in PSJ

We have used the Atacama Large Millimeter Array (ALMA) to measure precise absolute astrometric positions and detect the astrometric wobble of dwarf planet Orcus and its satellite Vanth over a complete orbit. We also place upper limits to the astrometric wobble induced by Dysnomia on dwarf planet Eris around its orbit. From the Vanth-Orcus barycentric motion, we find a Vanth-Orcus mass ratio of 0.16$\pm$0.02 -- the highest of any known planet or dwarf planet. This large ratio is consistent with the hypothesis that Vanth is a largely-intact impactor from a giant collision in the system, and that the system has likely evolved to a double synchronous state. We find only an upper limit of the barycenter motion of Eris, which implies a one sigma upper limit to the Dysnomia-Eris mass ratio of 0.0085, close to the modeled transition region between giant impact generated satellites which are largely intact remnants of the original impactor and those which form out of reaccreted disk material left over post-impact. The low albedo of Dysnomia leads us to marginally favor the intact impactor scenario. We find that Dysnomia has density of <1.2 g cm$^{-3}$, significantly lower than the 2.4 g cm$^{-3}$ of Eris., Comment: Planetary Science Journal, in press

JWST has shown that CO2 and CO are common on the surfaces of objects in the Kuiper belt and have apparent surface coverages even higher than that of water ice, though water ice is expected to be significantly more abundant in the bulk composition. Using full Mie scattering theory, we show that the high abundance and the unusual spectral behaviour around the 4.26 micron v1 band of CO2 can be explained by a surface covered in a few micron thick layer of ~ 1-2 micron CO2 particles. CO is unstable at the temperatures in the Kuiper belt, so the CO must be trapped in some more stable species. While hydrate clathrates or amorphous water ice are often invoked as a trapping mechanism for outer solar system ices, the expected spectral shift of the absorption line for a CO hydrate clathrates or trapping in amorphous ice is not seen, nor does the H2O abundance appear to be high enough to explain the depth of the CO absorption line. Instead, we suggest that the CO is created via irradiation of CO2 and trapped in the CO2 grains during this process. The presence of a thin surface layer of CO2 with embedded CO suggests volatile differentiation driving CO2 from the interior as a major process driving the surface appearance of these mid-sized Kuiper belt objects, but the mechanisms that control the small grain size and depth of the surface layer remain unclear., Comment: Planetary Science Journal, in press