We present simulations of lunar exospheric neon (20Ne) that include diurnal variations of the surface temperature measured by the Diviner radiometer onboard the Lunar Reconnaissance Orbiter (LRO). The Diviner-based model predicts a different exospheric density than the models based on analytical and empirical expressions of the surface temperature. The discrepancy is most evident in craters with a high abundance of rocks, which at night radiate more heat compared to the surrounding areas. We focus on Tycho, Tsiolkovskiy, and Giordano Bruno. For Tycho, the most prominent of these, the expected local depletion in exospheric density can be as great as similar to 18%, up to an altitude of similar to 20 km. This deviation could be detectable by a mass spectrometer orbiting the Moon at a few tens of kilometers of altitude. We compare the modeled exospheric densities with data from the Neutral Mass Spectrometer (NMS) onboard the Lunar Atmosphere and Dust Environment Explorer (LADEE). The Diviner-based model and the model based on the empirical formula of the surface temperature demonstrate superior agreement with the data, compared to the model based on analytical expression of the surface temperature. The radial profiles of exospheric 20Ne density at several lunar phases, latitudes, and local time show a common altitude (90-100 km) above which the exospheric density is greater on the dayside compared to the nightside, opposite to what is observed at lower altitudes. We find that charge exchange with solar wind protons is a negligible loss process for lunar exospheric 20Ne.

Observations of Europa’s leading hemisphere reveal elevated H _2 O _2 in the warmer, low-latitude chaos terrains compared to the colder, polar regions. This distribution disagrees with prior laboratory radiolysis studies of pure water ice, which show higher H _2 O _2 yields at colder temperatures. The regions with higher peroxide abundance, Tara and Powys Regiones, also present increased amounts of CO _2 , possibly sourced from Europa’s interior. To investigate whether CO _2 influences radiolysis of water ice to boost H _2 O _2 production, we irradiated water ice doped with varying amounts of CO _2 with 10 keV electrons at 70 and 100 K. Our results indicate that CO _2 , even in trace amounts (<3%), significantly enhances H _2 O _2 yields at temperatures relevant to Europa. We discuss the mechanisms by which CO _2 boosts peroxide synthesis and quantify H _2 O _2 creation and destruction cross sections and G -values across different CO _2 concentrations. These findings provide a plausible explanation for the perplexing H _2 O _2 distribution on Europa and has implications for understanding peroxide on other icy bodies such as Ganymede and Charon, where it has been detected alongside CO _2 .

The MAss Spectrometer for Planetary EXploration (MASPEX) is a high-mass-resolution, high-sensitivity, multi-bounce time-of-flight mass spectrometer (MBTOF) capable of measuring minor species with abundances of sub-parts-per-million in Europa’s sputter-produced and radiolytically modified exosphere and in its oceanic plumes. The goal of the MASPEX-Europa investigation is to determine, through in-situ measurement of the exosphere and plume composition, whether the conditions for habitability exist or have existed on Europa. As conventionally defined, based on our knowledge of Earth life, the three fundamental conditions for habitability are: (1) the presence of liquid water; (2) the presence of organic compounds and the biogenic elements CHNOPS; and (3) a source of energy available for metabolic processes, which for Europa will most probably be chemosynthetic rather than photosynthetic. Condition (1) is already established by previous indirect (magnetic field) measurements, while MASPEX will contribute directly to the evaluation of condition (2) through highly specific compositional measurements in the Europan exosphere and plumes. The composition measurements will also contribute to the test of condition (3) through disequilibrium states of chemical reactions. Thus, the primary goal of MASPEX for Europa Clipper is to assess the habitability of Europa and specifically of its interior ocean. MASPEX has been developed successfully, and its calibration has demonstrated that it meets its specified requirements for sensitivity, dynamic range, and mass resolution. This paper reports the development of the MASPEX scientific investigation, the instrument, its performance, and calibration.

Juno flew over the northern mid-latitudes of Ganymede during orbit 34 of the Juno mission, reaching an altitude of 1,053 km (16:56:07.972 UTC) at a sub spacecraft latitude/longitude of 33.66N, 57.5W degrees on 7 June 2021. Between 16:43 and 17:02 UT, Juno pierced Ganymede's magnetosphere at a velocity relative to Ganymede of 18.57 km s-1. Juno's instrumentation provided a unique opportunity to sample the local environment of Ganymede and its magnetosphere. We present measurements of the composition of the polar ionospheric outflow and the energetic electrons that penetrate Ganymede's atmosphere and produce its aurora. When these new observations are combined with modeling, conclusions can be drawn that affect our understanding of the atmosphere of Ganymede. The measured JADE precipitating plasma electrons provide an energy flux beyond that needed to create the observed oxygen emissions measured by UVS, but the electron energy spectrum is optically thin to the sparse atmosphere and does not provide the observed oxygen ultraviolet emission unless the O2 column density is increased by over an order of magnitude compared to previous atmospheric models. More than 99% of the electron energy flux passes through the atmosphere into the ice, thereby increasing the H2 and O2 content of the atmosphere. The increased H2 and O2 production is largely responsible for increasing the oxygen column density to a level that produces within known uncertainties the OI135.6 and OI130.4 nm emissions when bombarded by the electron energy flux observed by JADE. This suggests that past modeling efforts have underestimated the density of the atmosphere by over an order of magnitude. Juno flew by the Jovian satellite Ganymede on orbit 34 of the mission coming within 1,053 km of the surface at high northern latitudes. Juno provides a unique data set from the particle, field, and ultraviolet imaging experiments that can be utilized to study the interaction between the magnetosphere of Ganymede and the magnetosphere of Jupiter. Compositionally diverse ion outflow was observed in the northern polar cap that can be linked to the exchange of plasma and energetic particles between Jupiter and Ganymede. Furthermore, an electron spectrum produced by magnetic reconnection processes was observed that can be linked to the aurora at Ganymede. These observations provide new information about Ganymede's atmosphere. They strongly suggest an increase in the column density of O2 in Ganymede's atmosphere of an order of magnitude relative to all previous models. The latter has implications for all water ice satellites in the outer solar system. Multiple data sets from Juno's flyby of Ganymede indicate energetic particle impact of the surface and atmosphere resulting in ion outflow Reconnection processes on the Jupiter-facing flank of the magnetospheric interaction provide constraints on the auroral excitation Initial modeling strongly suggests an order of magnitude increase in atmospheric O2 column density relative to previous models

Jupiter's icy moon, Europa, harbors a subsurface liquid water ocean; the prospect of this ocean being habitable motivates further exploration of the moon with the upcoming NASA Europa Clipper mission. Key among the mission goals is a comprehensive assessment of the moon's composition, which is essential for assessing Europa's habitability. Through powerful remote sensing and in situ investigations, the Europa Clipper mission will explore the composition of Europa's surface and subsurface, its tenuous atmosphere, and the local space environment surrounding the moon. Clues on the interior composition of Europa will be gathered through these assessments, especially in regions that may expose subsurface materials, including compelling geologic landforms or locations indicative of recent or current activity such as potential plumes. The planned reconnaissance of the icy world will constrain models that simulate the ongoing external and internal processes that act to alter its composition. This paper presents the composition-themed goals for the Europa Clipper mission, the synergistic, composition-focused investigations that will be conducted, and how the anticipated scientific return will advance our understanding of the origin, evolution, and current state of Europa.

Studying the evolution of the surfaces and atmospheres of planetary bodies in the solar system is fundamental to our understanding of the present state of the solar system.Exospheres are the interfaces between the planetary body and the open space, so that, studying the exospheric filling and loss processes is the way to expand knowledge of the body's evolution.This endeavour entails finding variation of the rates of the ongoing processes as a function of the space environment, or, in other words, how the planetary space weather affects these bodies.Aside from occasional catastrophic events, such as volcanic eruptions and geysers in a few bodies or occasional impacts of comets and asteroids, surface and atmospheric changes are caused predominantly by the continuous bombardment of the bodies by photons, energetic ions, and micrometeoroids.While the exospheres are present around any kind of planetary body, they are quite different if we consider the bodies with an atmosphere and those without a collisional gas envelope.In fact, in the former case the exosphere is the upper part of the gas envelope where collisions become less and less frequent with altitude, so that, the boundary, the exobase, is a thick shell only conventionally defined as the surface where Knudsen number, Kn (the ratio of the mean free path over the atmospheric scale height), is equal to unity.On the contrary, in the latter case the exosphere is directly connected to the surface, thus, it is called surfacebounded exosphere, since the surface release processes are also the exospheric filling ones and atoms and molecules collide with the surface far more frequently than collisions with each other.In this case, the exobase is considered the surface itself, but it has quite different characteristics from the exosphere -atmosphere boundary.

Folder "CharonCode": Charon model code in MATLAB script, used in "Extreme Exospheric Dynamics at Charon: Implications for the Red Spot", Geophysical Research Letters, 2022, by Ben Teolis, Ujjwal Raut, Joshua A. Kammer, Caleb J. Gimar, Carly J. A. Howett, G. Randall Gladstone, Kurt D. Retherford. File "Fig2plotData.txt": Data for Figure 2 bottom plot, in "Extreme Exospheric Dynamics at Charon: Implications for the Red Spot", Geophysical Research Letters, 2022, by Ben Teolis, Ujjwal Raut, Joshua A. Kammer, Caleb J. Gimar, Carly J. A. Howett, G. Randall Gladstone, Kurt D. Retherford. Data gives the total CH4 molecules in the exospheric model and on the surface versus time, and the cumulative number of CH4 molecules photo-converted to surface photoproducts over one Pluto orbit. File "Fig4plotData.txt": Data for Figure 4 bottom plot, in "Extreme Exospheric Dynamics at Charon: Implications for the Red Spot", Geophysical Research Letters, 2022, by Ben Teolis, Ujjwal Raut, Joshua A. Kammer, Caleb J. Gimar, Carly J. A. Howett, G. Randall Gladstone, Kurt D. Retherford. Data gives the time-averaged frozen methane and photo-product distributions versus latitude at three different thermal inertias. The results are averaged over Pluto perihelion longitude to capture the estimated distributions over geologic time.

We investigate a possible negative ion feature observed by the Cassini Plasma Spectrometer (CAPS) during a flyby of Saturn's moon Dione that occurred on 7 April 2010. By examining possible particle trajectories, we find that the observed particles are consistent with negative pickup ions originating near the moon's surface. We find that the mass of the negative pickup ions is in the range of 15-25 u and tentatively identify this species as O-, likely resulting from ionization and subsequent pickup from Dione's O-2-CO2 exosphere. Our estimates show that the negative ion density is similar to 3 x 10(-3) cm(-3). This is comparable to, but slightly smaller than, that previously reported for the density of O-2(+) pickup ions for the same flyby, indicating that negative pickup ions may represent a major loss channel for Dione's exosphere.

The MAss Spectrometer for Planetary Exploration Europa is a high-resolution mass spectrometer that will fly onboard the Europa Clipper mission to explore the habitability of Europa. The inclusion of a cryotrap sampling system provides over three order of sensitivity enhancement over previous mass spectrometers flown onboard space missions.

During Cassini's final, spectacular months, in situ instruments made the first direct measurements of nanoparticles, finding an exceptionally large flow from the rings into Saturn's atmosphere. Cassini's Ion and Neutral Mass Spectrometer measured material in three altitude bands and found a global‐integrated flux of 2–20 × 10 4 kg/s that is dominated by hydrocarbon material <10 4 u. Ranging from clusters of a few molecules to radii of several nanometers, nanoparticles are ubiquitous throughout Saturn's rings but embedded in the regolith of larger particles and not detectable as independent particles using remote observations. The smallest nanoparticles are susceptible to atmosphere drag by Saturn's tenuous exosphere that reaches the inner edge of the D ring. The unsustainable large flux suggests a recent disturbance of Saturn's inner ring material, possibly associated with the clumping that appeared in the D68 ringlet in 2015.

The Pioneer and Voyager spacecraft made close-up measurements of Saturn's ionosphere and upper atmosphere in the 1970s and 1980s that suggested a chemical interaction between the rings and atmosphere. Exploring this interaction provides information on ring composition and the influence on Saturn's atmosphere from infalling material. The Cassini Ion Neutral Mass Spectrometer sampled in situ the region between the D ring and Saturn during the spacecraft's Grand Finale phase. We used these measurements to characterize the atmospheric structure and material influx from the rings. The atmospheric He/H2 ratio is 10 to 16%. Volatile compounds from the rings (methane; carbon monoxide and/or molecular nitrogen), as well as larger organic-bearing grains, are flowing inward at a rate of 4800 to 45,000 kilograms per second.

Saturn's largest icy moon, Rhea, hosts a tenuous surface-sputtered exosphere composed primarily of molecular oxygen and carbon dioxide. In this Letter, we examine Cassini Plasma Spectrometer velocity space distributions near Rhea and confirm that Cassini detected nongyrotropic fluxes of outflowing CO2+ during both the R1 and R1.5 encounters. Accounting for this nongyrotropy, we show that these possess comparable along-track densities of similar to 2x10(-3) cm(-3). Negatively charged pickup ions, also detected during R1, are surprisingly shown as consistent with mass 26 +/- 3 u which we suggest are carbon-based compounds, such as CN-, C2H-, C-2(-), or HCO-, sputtered from carbonaceous material on the moon's surface. The negative ions are calculated to possess along-track densities of similar to 5x10(-4) cm(-3) and are suggested to derive from exogenic compounds, a finding consistent with the existence of Rhea's dynamic CO2 exosphere and surprisingly low O-2 sputtering yields. These pickup ions provide important context for understanding the exospheric and surface ice composition of Rhea and of other icy moons which exhibit similar characteristics.

M. E. Perry, J. H. Waite, Jr., R. S. Perryman, D. G. Mitchell, T. E. Cravens, L. Moore, K. E. Miller, R. V. Yelle, B. D. Teolis, R. L. McNutt, Jr.; Johns Hopkins Applied Physics Laboratory, 11100 Johns Hopkins Road, Laurel, MD. Southwest Research Institute, San Antonio, TX. Department of Physics and Astronomy, University of Kansas, Lawrence, Kansas. Center for Space Physics, Boston University, Boston, MA. Department of Planetary Sciences, University of Arizona, Tucson, AZ.

During three low-altitude (99, 66, 66 km) flybys through the Enceladus plume in 2010 and 2011, Cassini's ion neutral mass spectrometer (INMS) made its first high spatial resolution measurements of the plume's gas density and distribution, detecting in situ the individual gas jets within the broad plume. Since those flybys, more detailed Imaging Science Subsystem (ISS) imaging observations of the plume's icy component have been reported, which constrain the locations and orientations of the numerous gas/grain jets. In the present study, we used these ISS imaging results, together with ultraviolet imaging spectrograph stellar and solar occultation measurements and modeling of the three-dimensional structure of the vapor cloud, to constrain the magnitudes, velocities, and time variability of the plume gas sources from the INMS data. Our results confirm a mixture of both low and high Mach gas emission from Enceladus' surface tiger stripes, with gas accelerated as fast as Mach 10 before escaping the surface. The vapor source fluxes and jet intensities/densities vary dramatically and stochastically, up to a factor 10, both spatially along the tiger stripes and over time between flyby observations. This complex spatial variability and dynamics may result from time-variable tidal stress fields interacting with subsurface fissure geometry and tortuosity beyond detectability, including changing gas pathways to the surface, and fluid flow and boiling in response evolving lithostatic stress conditions. The total plume gas source has 30% uncertainty depending on the contributions assumed for adiabatic and nonadiabatic gas expansion/acceleration to the high Mach emission. The overall vapor plume source rate exhibits stochastic time variability up to a factor similar to 5 between observations, reflecting that found in the individual gas sources/jets.