arXiv subjects

L. Roth

Publications and source records attributed to L. Roth.

8 recordsLinked to original sources

arXiv2026

Europa's Lyman-$\alpha$ emissions from HST/STIS observations

An image of Lyman-$\alpha$ (Ly$\alpha$) emission from Europa obtained with the Hubble Space Telescope Space Telescope Imaging Spectrograph (HST/STIS) has previously provided the first evidence of localized water vapor (H$_2$O) aurora, potentially originating from outgassing. Subsequent STIS observations have revealed the presence of a global atomic hydrogen (H) exosphere. We present a comprehensive analysis of STIS Ly$\alpha$ 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. We analyze the complete dataset of STIS observations obtained when Europa was sunlit and not transiting Jupiter. A forward model is constructed to account for all known sources of Ly$\alpha$ emission, including resonantly scattered sunlight from Europa's H exosphere. To identify localized anomalies, such as H$_2$O aurora, the modeled Ly$\alpha$ emission is subtracted and the residuals are examined. Emission from Europa's H exosphere is detected at all observing epochs, but is attenuated by absorption in Earth's exosphere when Europa's radial velocity relative to Earth (and thus the Doppler shift) is small. From the velocity dependence of this attenuation, we estimate an H-exosphere temperature of $\sim 1000$ K and derive an upper limit of 5100 K. For the best-constrained epoch in 2014--2015, we infer a vertical H column density of $1.4x10^{12}$ cm$^{-2}$ and an H source rate of $1.1x10^{27}$ s$^{-1}$. No localized emission enhancements are detected in any of the observations, including the image previously interpreted as evidence of H$_2$O 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, as well as from the inclusion of an H-exosphere signal in the present analysis...

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arXiv2025

Revealing Io's Surface using JWST-NIRISS Aperture Masking Interferometry and Neural Network Deconvolution

Io is one of Jupiter's largest moons and the most volcanically active body in the Solar System. Its very active surface has hot spots produced by volcanic eruptions popping up at seemingly random locations and times. Characterizing the complex surface of Io requires the highest angular resolution available. This work presents the analysis of Aperture Masking Interferometric observations (at 4.3 um) of Io taken with the Near-Infrared Imager and Slitless Spectrograph instrument on the James Webb Space Telescope. These are the first space-based infrared interferometric observations of a Solar System body ever taken. For complex extended objects like Io, the traditional visibility extraction algorithms from interferograms suffer from limitations. Here, new deconvolution methods based on Neural Networks allowed us to obtain reliable images from which a detailed analysis of the volcanically active surface of this moon was performed. Our study characterizes the loci and brightness of several unresolved volcanoes on the surface of Io, as well as the extended emission observed. We identified the brightest eruption (I_4.3um = 33 +/- 4.3 GW/um), referred to as V1, within an area to the North-East of Seth Patera (129.4 +/- 0.8 deg. W. Longitude, 1.5 +/- 0.7 deg. S. Latitude). Its projected speed (V_T = 86 +/- 34 m/s) is consistent with the rotational speed of Io. Additionally, six fainter volcanoes were identified and characterized. Complementary ground-based images, taken with the Keck II telescope, allowed us to benchmark the deconvolved Aperture Masking Interferometric images, showing consistency. Finally, we highlight the importance of characterizing Io's surface with long-term monitoring at high-angular resolution.

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arXiv2025

Study of the atmospheric effects of energetic particle precipitations on giant planets with HWO

UV auroral emissions from giant planets are produced by extra-atmospheric energetic particles interacting with an atmosphere. They have been observed on Jupiter, Saturn and Uranus and should be present on Neptune. Even if the mechanisms are similar, each planet is unique due to its specific source of magnetospheric plasma and the structure and dynamics of its magnetosphere. How these precipitations modify atmospheric heating, dynamics and chemical balance at local and global atmospheric scale is still poorly known, especially on Uranus and Neptune, and critical to understanding the global atmosphere-magnetosphere system of giant planets and exoplanets. In this manucript we present how future observations by instruments, aboard \textit{the Habitable World Observatory} (HWO) will provide new information to better understand the origin and the atmospheric effects of these precipitations. A major interest is for the distant magnetospheres of Uranus and Neptune, never explored by an orbital spacecraft whose UV auroral emissions remains at (Uranus) or below (Neptune) the HST sensitivity. \textit{Pollux} is one such UV instrument concept, which will enable unprecedented high spectral resolution at fine spatial scale not previously seen and polarimetric observations of the planetary aurorae while \textit{LUMOS}, another UV instrument will image the full auroral regions with a good spectral resolution.

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arXiv2024

Mass supply from Io to Jupiter's magnetosphere

Since the Voyager mission flybys in 1979, we have known the moon Io to be both volcanically active and the main source of plasma in the vast magnetosphere of Jupiter. Material lost from Io forms neutral clouds, the Io plasma torus and ultimately the extended plasma sheet. This material is supplied from Io's upper atmosphere and atmospheric loss is likely driven by plasma-interaction effects with possible contributions from thermal escape and photochemistry-driven escape. Direct volcanic escape is negligible. The supply of material to maintain the plasma torus has been estimated from various methods at roughly one ton per second. Most of the time the magnetospheric plasma environment of Io is stable on timescales from days to months. Similarly, Io's atmosphere was found to have a stable average density on the dayside, although it exhibits lateral and temporal variations. There is potential positive feedback in the Io torus supply: collisions of torus plasma with atmospheric neutrals are probably a significant loss process, which increases with torus density. The stability of the torus environment may be maintained by limiting mechanisms of either torus supply from Io or the loss from the torus by centrifugal interchange in the middle magnetosphere. Various observations suggest that occasionally the plasma torus undergoes major transient changes over a period of several weeks, apparently overcoming possible stabilizing mechanisms. Such events are commonly explained by some kind of change in volcanic activity that triggers a chain of reactions which modify the plasma torus state via a net change in supply of new mass. However, it remains unknown what kind of volcanic event (if any) can trigger events in torus and magnetosphere, whether Io's atmosphere undergoes a general change before or during such events, and what processes could enable such a change in the otherwise stable torus.

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arXiv2023

The RATT PARROT: serendipitous discovery of a peculiarly scintillating pulsar in MeerKAT imaging observations of the Great Saturn-Jupiter Conjunction of 2020. I. Dynamic imaging and data analysis

We report on a radiopolarimetric observation of the Saturn-Jupiter Great Conjunction of 2020 using the MeerKAT L-band system, initially carried out for science verification purposes, which yielded a serendipitous discovery of a pulsar. The radiation belts of Jupiter are very bright and time variable: coupled with the sensitivity of MeerKAT, this necessitated development of dynamic imaging techniques, reported on in this work. We present a deep radio "movie" revealing Jupiter's rotating magnetosphere, a radio detection of Callisto, and numerous background radio galaxies. We also detect a bright radio transient in close vicinity to Saturn, lasting approximately 45 minutes. Follow-up deep imaging observations confirmed this as a faint compact variable radio source, and yielded detections of pulsed emission by the commensal MeerTRAP search engine, establishing the object's nature as a radio emitting neutron star, designated PSR J2009-2026. A further observation combining deep imaging with the PTUSE pulsar backend measured detailed dynamic spectra for the object. While qualitatively consistent with scintillation, the magnitude of the magnification events and the characteristic timescales are odd. We are tentatively designating this object a pulsar with anomalous refraction recurring on odd timescales (PARROT). As part of this investigation, we present a pipeline for detection of variable sources in imaging data, with dynamic spectra and lightcurves as the products, and compare dynamic spectra obtained from visibility data with those yielded by PTUSE. We discuss MeerKAT's capabilities and prospects for detecting more of such transients and variables.

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arXiv2023

Composition and thermal properties of Ganymede's surface from JWST/NIRSpec and MIRI observations

JWST NIRSpec IFU (2.9-5.3 mu) and MIRI MRS (4.9-28.5 mu) observations were performed on both the leading and trailing hemispheres of Ganymede with a spectral resolution of ~2700. Reflectance spectra show signatures of water ice, CO2 and H2O2. An absorption feature at 5.9 mu is revealed and is tentatively assigned to sulfuric acid hydrates. The CO2 4.26-mu band shows latitudinal and longitudinal variations in depth, shape and position over the two hemispheres, unveiling different CO2 physical states. In the ice-rich polar regions, which are the most exposed to Jupiter's plasma irradiation, the CO2 band is redshifted with respect to other terrains. In the leading northern polar cap, the CO2 band is dominated by a high wavelength component at ~4.27 mu, consistent with CO2 trapped in amorphous water ice. At equatorial latitudes (and especially on dark terrains) the observed band is broader and shifted towards the blue, suggesting CO2 adsorbed on non-icy materials. Amorphous ice is detected in the ice-rich polar regions, and is especially abundant on the leading northern polar cap. In both hemispheres the north polar cap ice appears to be more processed than the south polar cap. A longitudinal modification of the H2O ice molecular structure and/or nano/micrometre-scale texture, of diurnal or geographic origin, is observed in both hemispheres. Ice frost is observed on the morning limb of the trailing hemisphere, possibly formed during the night from the recondensation of water subliming from the warmer subsurface. Reflectance spectra of the dark terrains are compatible with the presence of Na-/Mg-sulfate salts, sulfuric acid hydrates, and possibly phyllosilicates mixed with fine-grained opaque minerals, having an highly porous texture. Mid-IR brightness temperatures indicate a rough surface and a very low thermal inertia of 20-40 J m-2 s-0.5 K-1, consistent with a porous surface.

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arXiv2023

JWST molecular mapping and characterization of Enceladus' water plume feeding its torus

Enceladus is a prime target in the search for life in our solar system, having an active plume likely connected to a large liquid water subsurface ocean. Using the sensitive NIRSpec instrument onboard JWST, we searched for organic compounds and characterized the plume's composition and structure. The observations directly sample the fluorescence emissions of H2O and reveal an extraordinarily extensive plume (up to 10,000 km or 40 Enceladus radii) at cryogenic temperatures (25 K) embedded in a large bath of emission originating from Enceladus' torus. Intriguingly, the observed outgassing rate (300 kg/s) is similar to that derived from close-up observations with Cassini 15 years ago, and the torus density is consistent with previous spatially unresolved measurements with Herschel 13 years ago, suggesting that the vigor of gas eruption from Enceladus has been relatively stable over decadal timescales. This level of activity is sufficient to maintain a derived column density of 4.5x1017 m-2 for the embedding equatorial torus, and establishes Enceladus as the prime source of water across the Saturnian system. We performed searches for several non-water gases (CO2, CO, CH4, C2H6, CH3OH), but none were identified in the spectra. On the surface of the trailing hemisphere, we observe strong H2O ice features, including its crystalline form, yet we do not recover CO2, CO nor NH3 ice signatures from these observations. As we prepare to send new spacecraft into the outer solar system, these observations demonstrate the unique ability of JWST in providing critical support to the exploration of distant icy bodies and cryovolcanic plumes.

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arXiv2020

An attempt to detect transient changes in Io's SO2 and NaCl atmosphere

Io's atmosphere is predominately SO2 sustained by a combination of volcanic outgassing and sublimation. The loss from the atmosphere is the main mass source for Jupiter's large magnetosphere. Previous studies attributed various transient phenomena in Io's environment and Jupiter's magnetosphere to a sudden change in the mass loss from the atmosphere supposedly triggered by a change in volcanic activity. Since the gas in volcanic plumes does not escape directly, such causal correlation would require a transient volcano-induced change in atmospheric abundance, which has never been observed so far. Here we report four observations of atmospheric SO2 and NaCl obtained with the IRAM NOEMA interferometer. These observations are compared to measurements of volcanic hot spots and Io's neutral and plasma environment. We find a stable NaCl column density in Io's atmosphere. The SO2 column density derived for December 2016 is about 30% lower compared to the period of March to April 2017. This increase in SO2 from December 2016 to March 2017 might be related to increasing volcanic activity observed at several sites in spring 2017, but the stability of the volcanic trace gas NaCl and resulting decrease in NaCl/SO2 ratio do not support this interpretation. Observed dimmings in both the sulfur ion torus and Na neutral cloud suggest rather a decrease in mass loading in the period of increasing SO2 abundance. The dimming Na brightness and stable atmospheric NaCl furthermore dispute an earlier suggested positive correlation of the sodium cloud and the hot spot activity at Loki Patara, which considerably increased in this period. The environment of Io overall appears to be in a quiescent state, preventing further conclusions. Only Jupiter's aurora morphology underwent several short-term changes, which are apparently unrelated to Io's quiescent environment or the relatively stable atmosphere.

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