Central Arizona College

Context. An image of Lyman-α (Lyα) emission from Europa obtained with the Hubble Space Telescope’s Space Telescope Imaging Spectrograph (HST/STIS) has provided the first evidence of localized water vapor (H2O) aurora, potentially originating from outgassing. Subsequent STIS observations have revealed the presence of a global atomic hydrogen (H) exosphere at Europa. Aims. We present a comprehensive analysis of STIS Lyα observations of Europa acquired in 1999 and between 2012 and 2020 to search for localized auroral emissions and constrain the properties of Europa’s H exosphere. Methods. We analyzed the complete dataset of the STIS observations obtained when Europa was sunlit and not transiting Jupiter. We constructed a model that accounts for all known sources of Lyα emission, including resonantly scattered sunlight from Europa’s H exosphere. To identify localized anomalies, such as H2O aurora, we subtracted the modeled Lyα emission and analyzed the residuals. Results. We detected emission from Europa’s H exosphere at all observing epochs, but we found that it is attenuated by absorption in Earth’s exosphere when Europa’s radial velocity relative to Earth (and, thus, the Doppler shift) is low. From the velocity dependence of this attenuation, we estimated an H-exosphere temperature of ∼1000 K and derived an upper limit of 5100 K. For the best-constrained epoch in 2014/2015, we inferred a vertical H column density of 1.4 × 1012 cm−2 and an H source rate of 1.1 × 1027 s−1. No localized emission enhancements were detected in any of the observations, including the image previously interpreted as evidence of H2O aurora near Europa’s south pole. The discrepancy with earlier results arises primarily from differences in the assumed position of Europa’s disk on the detector. The inclusion of an H-exosphere signal in the present analysis also contributes to this difference. When adopting the same disk position as in the previous study and neglecting the H-exosphere signal, the localized emission enhancement was again detected with a similar statistical significance. However, because of the updated approach to disk positioning and the more complete modeling of emission sources, including the H exosphere, we consider the results presented here as the preferred interpretation. Conclusions. We find evidence to support a persistent hydrogen exosphere at Europa, but no evidence of localized water vapor.

Background: Objective assessment of preclinical dental practices remains challenging, as it requires consistency, transparency, and standardization in the evaluation of practical competencies. Rubrics have been proposed as useful tools for improving the quality of assessment; however, evidence regarding their psychometric properties in preclinical orthodontic education remains limited. Aim: This study aimed to analyze the reliability, internal structure, and academic usefulness of assessment rubrics applied to preclinical orthodontic practice in undergraduate dental education. Methods: A cross-sectional psychometric retrospective study was conducted with 175 third-year dentistry students enrolled in Orthodontics I at the European University of Madrid. Two analytical rubrics designed to assess wire-bending and cephalometry practices were evaluated. Reliability was assessed using Cronbach’s alpha, construct validity using exploratory factor analysis, and associations with academic performance by correlation analyses. Results: The wire-bending rubric showed moderate internal consistency (α = 0.61), whereas the cephalometry rubric demonstrated adequate reliability (α = 0.71). Exploratory factor analysis yielded evidence consistent with a one-dimensional structure for both instruments. Cephalometry performance was positively associated with theoretical examination scores and seminar performance, whereas no significant associations were observed for wire-bending performance. Students reported generally positive perceptions of rubric use, although lower post-assessment ratings were observed in the wire-bending activity. Conclusions: These findings provide preliminary evidence supporting the reliability and educational usefulness of rubric-based assessment in preclinical orthodontic education. These instruments may contribute to greater transparency and consistency in student assessment. Further studies involving multiple evaluators, multicenter samples, longitudinal designs, and psychometric approaches specifically developed for ordinal data are required.

We present the first spatially resolved images of Lyman-alpha (Ly alpha) emissions from Uranus taken by the Hubble Space Telescope (HST). The observations were carried out using HST's Space Telescope Imaging Spectrograph instrument as part of two far-ultraviolet (FUV) observing campaigns in 1998 and 2011, before and after Uranus' equinox in 2007. The average intensities (+/- uncertainties) on Uranus' disk were 860 +/- 6 and 725 +/- 9 R, respectively. The images reveal widely extended emissions, detectable up to similar to 4 Uranus radii (R-U). We performed simulations of the Ly alpha radiative transfer in the atmosphere, considering resonant scattering by H, Rayleigh scattering by H-2, and absorption by CH4. We considered only solar Ly alpha fluxes at Uranus as the Ly alpha source for simulations. The effects of hydrogen in the interplanetary medium and Earth's exosphere on Uranus' Ly alpha emissions were taken into account. We find a good agreement between on-disk brightnesses from simulations and the HST observations assuming the (H, H-2, and CH4) atmosphere profile derived from Voyager 2 measurements. Only slight adjustments of the H or H-2 densities were required in some of the simulation cases, in particular, for the 1998 observations. To match the off-disk HST brightnesses in both years, a substantial exosphere of gravitationally bound hot H is required, which we modelled assuming the hot H number density has a Chapman profile. We find that compared to 1998, the hot H abundance required for 2011 is lower and the inferred hot H profiles seem to be more extended. This bound hot H is likely to be a persistent part of Uranus' upper atmosphere and is distinct from the escaping hot H population derived from Voyager 2 observations. We discuss the possible production mechanisms involving solar EUV radiation and study the sensitivity of the modelled brightness to the parameters of the hot H profile. We find that solar EUV radiation is not a sufficient source to explain the hot H in the exosphere of Uranus.

During 2023 September the Alice ultraviolet spectrograph on the New Horizons (NH) spacecraft was used to map diffuse Lyα emission over most of the sky, at a range of ∼56.9 au from the Sun. At that distance, models predict that the interplanetary medium Ly α emissions result from comparable amounts of resonant backscattering of the solar Ly α line by interstellar hydrogen atoms (H i ) passing through the solar system, in addition to an approximately isotropic background of ∼50 ± 20 R from the local interstellar medium (LISM). The NH observations show no strong correlations with nearby cloud structures of the LISM or with expected structures of the heliosphere, such as a hydrogen wall associated with the heliopause. To explain the relatively bright and uniform Ly α of the LISM, we propose that hot, young stars within the Local Hot Bubble shine on its interior walls, photoionizing H i atoms there. Recombination of these ions can account for the observed ∼50 R Ly α background, after amplification of the diffuse Ly α by resonant scattering, although sophisticated (i.e., 3D) radiative transfer models should be used to confirm this conjecture. Future observations of the diffuse Ly α , with instruments capable of resolving the line profile, could provide a new window on H i populations in the LISM and heliosphere. The NH Alice all-sky Ly α observations presented here may be repeated at some point in the future, if resources allow, and the two maps could be combined to provide a significant increase in angular resolution.

This article demonstrates the author’s ecopedagogical teaching model through text and image. I explain how I created a teaching framework based on culturally relevant and sustaining pedagogy but felt that the framework fell short in not including an earth-inclusive focus and ecojustice ethic. Through revision and re-envisioning, I arrived at a place-based ecopedagogical model of a saguaro cactus where multiple arms and the base represent eco-inclusive facets of this framework. I encourage other educators to consider how they, too, might create ecopedagogical frameworks for their own teaching.