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Reflected sunlight observations from the Ultraviolet Spectrograph (UVS) on the Juno spacecraft were used to study the distribution of acetylene (C$_2$H$_2$) at Jupiter's south pole. We find that the shape of the C$_2$H$_2$ absorption feature varies significantly across the polar region, and this can be used to infer spatial variability in the C$_2$H$_2$ abundance. There is a localized region of enhanced C$_2$H$_2$ absorption which coincides with the location of Jupiter's southern polar aurora; the C$_2$H$_2$ abundance poleward of the auroral oval is a factor of 3 higher than adjacent quiescent, non-auroral longitudes. This builds on previous infrared studies which found enhanced C$_2$H$_2$ abundances within the northern auroral oval. This suggests that Jupiter's upper-atmosphere chemistry is being strongly influenced by the influx of charged auroral particles and demonstrates the necessity of developing ion-neutral photochemical models of Jupiter's polar regions., Accepted in JGR: Planets

The UVS instrument on the Juno mission records far-ultraviolet reflected sunlight from Jupiter. These spectra are sensitive to the abundances of chemical species in the upper atmosphere and to the distribution of the stratospheric haze layer. We combine observations from the first 30 perijoves of the mission in order to study the meridional distribution of acetylene (C$_2$H$_2$) in Jupiter's stratosphere. We find that the abundance of C$_2$H$_2$ decreases towards the poles by a factor of 2-4, in agreement with previous analyses of mid-infrared spectra. This result is expected from insolation rates: near the equator, the UV solar flux is higher, allowing more C$_2$H$_2$ to be generated from the UV photolysis of CH$_4$. The decrease in abundance towards the poles suggests that horizontal mixing rates are not rapid enough to homogenize the latitudinal distribution., Accepted in JGR Planets. 19 pages, 3 figures

The UVS instrument on the Juno mission recorded transient bright emission from a point source in Jupiter's atmosphere. The spectrum shows that the emission is consistent with a 9600-K blackbody located 225 km above the 1-bar level and the duration of the emission was between 17 ms and 150 s. These characteristics are consistent with a bolide in Jupiter's atmosphere. Based on the energy emitted, we estimate that the impactor had a mass of 250-5000 kg, which corresponds to a diameter of 1-4 m. By considering all observations made with Juno UVS over the first 27 perijoves of the mission, we estimate an impact flux rate of 24,000 per year for impactors with masses greater than 250-5000 kg., Comment: Accepted in GRL. 21 pages, 3 figures

We describe the radiometric performance and ground calibration results of the JUpiter ICy moons Explorer Ultraviolet Spectrograph (JUICE-UVS) instrument. JUICE-UVS is a modest power (8 W) ultraviolet spectrograph that is the fifth in a series of Alice/UVS instruments built by Southwest Research Institute. JUICE-UVS covers a 50-204 nm bandpass with 0.4 nm spectral resolution over a 7.5° field of view with better than 0.3° spatial resolution. JUICE-UVS also features three different observing modes to allow higher-than-nominal spatial resolution observing as well as solar occultations in the Jupiter system. JUICE-UVS meets all performance requirements with margin, and is the first planetary UV spectrograph to feature a microchannel plate detector with an atomic layer deposition (ALD) coating to minimize in-flight gain loss due to accumulated fluence. JUICE-UVS also features both a time-tagged pixel list observing mode and a programmable histogram mode to maximize observational flexibility and data management. During the main JUICE mission, JUICE-UVS will explore the atmospheres and surfaces of the Galilean satellites, examine the dynamics of Jupiter’s upper atmosphere from pole to equator, and investigate the Jupiter-Io connection through observations of the Io torus.

11 transient bright flashes were detected in Jupiter's atmosphere using the UVS instrument on the Juno spacecraft. These bright flashes are only observed in a single spin of the spacecraft and their brightness decays exponentially with time, with a duration of ~1.4 ms. The spectra are dominated by H2 Lyman band emission and based on the level of atmospheric absorption, we estimate a source altitude of 260 km above the 1-bar level. Based on these characteristics, we suggest that these are observations of Transient Luminous Events (TLEs) in Jupiter's upper atmosphere. In particular, we suggest that these are elves, sprites or sprite halos, three types of TLEs that occur in the Earth's upper atmosphere in response to tropospheric lightning strikes. This is supported by visible light imaging, which shows cloud features typical of lightning source regions at the locations of several of the bright flashes. TLEs have previously only been observed on Earth, although theoretical and experimental work has predicted that they should also be present on Jupiter., Comment: Accepted in JGR: Planets. 28 pages, 8 figures

On February 7th 2018, during Juno’s 11th perijove observation sequence, Juno’s ultraviolet spectrograph (Juno-UVS) unveiled the development of a dawn storm in Jupiter's aurorae. These auroral events consist of spectacular brightenings of the midnight to dawn sector of the main emissions at Jupiter. At the end of the sequence, Juno crossed the magnetic field lines connected to this dawn storm, unraveling some of the processes giving rise to these spectacular events. All in situ instruments detected a sharp transition as the spacecraft entered the dawn storm at an altitude of approximately 5RJ in the southern hemisphere. The particle fluxes detected by the JADE and JEDI instruments, including electrons and ions, increased dramatically. A strong flux of penetrating radiation was also detected by the UVS instrument. The Alfvén waves spectrograms derived from the MAG instrument also show a clear transition between a quiet and an extremely active regime as the spacecraft entered the dawn storm. Furthermore, the orientation of the magnetic field showed a very strong perturbation, associated with intense currents. And, finally, intense bKOM emissions were also observed during this time interval. Combined with the remote sensing observations of the aurora, these datasets strongly suggest that Juno witnessed a strong magnetospheric reconfiguration that started in the magneto-tail and then evolved toward dawn as the planet rotated.

In July of 2016, NASA began a new era in Jupiter exploration by placing the Juno spacecraft and its highly capable suite of scientific instrumentation in a polar orbit about Jupiter. It was a unique opportunity to study Jupiter’s auroras in great details with the Ultraviolet Spectrograph (UVS) instrument during the first 25 perijoves. Here we present a systematic analysis of a newly identified feature of the polar emissions called the auroral bright spot. The bright spots have power ranging from tens to a hundred gigawatts. In a given perijove, bright spot reoccurs at almost the same system III (SIII) position within a time interval of a few to tens of minutes. Furthermore, we found a brightness quasiperiodicity of 22-28 minutes in the southern bright spots observed during perijove 4 and perijove 16. The northern bright spots locate in a confined region, near 175° SIII longitude and 65 degrees latitude, while the southern spots scatter randomly around the pole. The bright spots’ positions reported here are usually located on the edge of the swirl region (the polar-most region of Jupiter’s auroras). This feature is observed at all magnetic local times rather than being confined to the noon sector. Therefore, the bright spot is incompatible with the auroral signature of Earth-like Sun-facing cusp, as proposed in earlier works. However, due to Jupiter's rapid rotation with respect to the size of the magnetosphere, the topology of the cusp region at Jupiter is expected to be considerably complicated by the twisting of the field lines. Hence, we cannot conclude whether the bright spot is related to the Jovian cusp processes yet. Finally, we also have identified time intervals during which Juno flew through the field lines connected to the bright spot allowing further investigations of the associated particles and responsible processes.

Polar aurorae are a direct consequence of the dynamics of the plasma in the magnetosphere. The sources of mass and energy differ between the Earth’s and Jupiter’s magnetospheres, hence leading to f...

During the New Horizons spacecraft's encounter with Pluto, the Alice ultraviolet spectrograph conducted a series of observations that detected emissions from both the interplanetary medium (IPM) and Pluto. In the direction of Pluto, the IPM was found to be 133.4$\pm$0.6R at Lyman $\alpha$, 0.24$\pm$0.02R at Lyman $\beta$, and, Comment: 27 pages, 8 figures

Recent observations of interplanetary medium (IPM) atomic hydrogen Lyman-{\alpha} (Ly{\alpha}) emission in the outer solar system, made with the Alice ultraviolet spectrograph on New Horizons (NH), are presented. The observations include regularly spaced great-circle scans of the sky and pointed observations near the downstream and upstream flow directions of interstellar H atoms. The NH Alice data agree very well with the much earlier Voyager UVS results, after these are reduced by a factor of 2.4 in brightness, in accordance with recent re-analyses. In particular, the falloff of IPM Ly{\alpha} brightness in the upstream-looking direction as a function of spacecraft distance from the Sun is well-matched by an expected 1/r dependence, but with an added constant brightness of ~40 Rayleighs. This additional brightness is a possible signature of the hydrogen wall at the heliopause or of a more distant background. Ongoing observations are planned at a cadence of roughly twice per year., Comment: 21 pages, 5 figures, 1 table, accepted for publication in Geophys. Res. Lett

We describe the stray and scattered light properties of the Juno Ultraviolet Spectrograph (Juno-UVS). Juno-UVS is a modest-powered (9.0 W) instrument that is designed to characterize Jupiter’s auroral emissions and relate them to in situ measurements made by Juno’s particle and wave instruments. A notable scattered light feature has been discovered during UVS operations; a minor solar glint that reveals itself during specific spacecraft orientations when the spin axis is pointed a certain angle away from the sun. This scattered light feature has become more important now that the Juno mission has decided to stay in its 53-day parking orbit instead of transitioning to the planned 14-day science orbit. The impact of the scattered light feature on future instrument operations is discussed.

The Juno Ultraviolet Spectrograph (Juno-UVS) is a remote-sensing science instrument onboard the Juno spacecraft that has been in polar orbit around Jupiter since July 2016. Juno-UVS measures photon events in the ultraviolet from about 68 to 210 nm. It is primarily used to observe emission from the Jovian aurorae, but is also sensitive to other sources such as UV-bright stars, sky background Lyman-alpha emission, and reflected sunlight. However, Juno-UVS is also sensitive to the effects of penetrating high-energy radiation, which results in elevated count rates as measured by the instrument detector array. This radiation presents a challenge for efficiently planning the acquisition of mission science data, as data volume is a valuable (and finite) resource that can quickly be filled when the spacecraft periodically passes through regions of high radiation. This background radiation has been found to vary significantly on both short (spacecraft spin-modulated) time scales, as well as longer timescales from minutes to hours during each close approach to Jupiter. This variability has required a multi-pronged approach in the operation planning of hardware (such as dynamic instrument voltage adjustment) as well as onboard software (such as utilizing data quality factors for the selective storage of science data). We present an overview of these current mitigation/optimization techniques and planning strategies used for this instrument, which will likely also be useful for the development and operations of future instruments within high radiation space environments (e.g., the ESA JUICE mission or NASA’s Europa Clipper).

This paper explores the uniqueness of ESA Rosetta mission operations from the Alice ultraviolet spectrograph instrument point of view, documents lessons learned, and suggests operations ideas for f...

The Alice instrument on NASA's New Horizons spacecraft observed an ultraviolet solar occultation by Pluto's atmosphere on 2015 July 14. The transmission vs. altitude was sensitive to the presence of N_2, CH_4, C_2H_2, C_2H_4, C_2H_6, and haze. We derived line-of-sight abundances and local number densities for the 5 molecular species, and line-of-sight optical depth and extinction coefficients for the haze. We found the following major conclusions: (1) We confirmed temperatures in Pluto's upper atmosphere that were colder than expected before the New Horizons flyby, with upper atmospheric temperatures near 65–68 K. The inferred enhanced Jeans escape rates were (3–7) × 10^(22) N_2 s^(−1) and (4–8) × 10^(25) CH_4 s^(−1) at the exobase (at a radius of ∼ 2900 km, or an altitude of ∼1710 km). (2) We measured CH_4 abundances from 80 to 1200 km above the surface. A joint analysis of the Alice CH_4 and Alice and REX N_2 measurements implied a very stable lower atmosphere with a small eddy diffusion coefficient, most likely between 550 and 4000 cm^2 s^(−1). Such a small eddy diffusion coefficient placed the homopause within 12 km of the surface, giving Pluto a small planetary boundary layer. The inferred CH_4 surface mixing ratio was ∼ 0.28–0.35%. (3) The abundance profiles of the “C_2H_x hydrocarbons” (C_2H_2, C_2H_4, C_2H_6) were not simply exponential with altitude. We detected local maxima in line-of-sight abundance near 410 km altitude for C_2H_4, near 320 km for C_2H_2, and an inflection point or the suggestion of a local maximum at 260 km for C_2H_6. We also detected local minima near 200 km altitude for C_2H_4, near 170 km for C_2H_2, and an inflection point or minimum near 170–200 km for C_2H_6. These compared favorably with models for hydrocarbon production near 300–400 km and haze condensation near 200 km, especially for C_2H_2 and C_2H_4 (Wong et al., 2017). (4) We found haze that had an extinction coefficient approximately proportional to N_2 density.

The Lunar Reconnaissance Orbiter’s (LRO) Lyman Alpha Mapping Project (LAMP) is a lightweight (6.1 kg), lowpower (4.5 W), ultraviolet spectrograph based on the Alice instruments aboard the European Space Agency’s Rosetta spacecraft and NASA’s New Horizons spacecraft. Its primary job is to identify and localize exposed water frost in permanently shadowed regions (PSRs) near the Moon’s poles, and to characterize landforms and albedos in PSRs. LRO launched on June 18, 2009 and reached lunar orbit four days later. LAMP operated with its failsafe door closed for its first seven years in flight. The failsafe door was opened in October 2016 to increase light throughput during dayside operations at the expense of no longer having the capacity to take further dark observations and slightly more operational complexity to avoid saturating the instrument. This one-time irreversible operation was approved after extensive review, and was conducted flawlessly. The increased throughput allows measurement of dayside hydration in one orbit, instead of averaging multiple orbits together to reach enough signal-to-noise. The new measurement mode allows greater time resolution of dayside water migration for improved investigations into the source and loss processes on the lunar surface. LAMP performance and optical characteristics after the failsafe door opening are described herein, including the new effective area, wavelength solution, and resolution.

The Juno Ultraviolet Spectrograph (Juno-UVS) is a remote-sensing science instrument onboard the Juno spacecraft that has been in polar orbit around Jupiter since July 2016. Juno-UVS measures photon events in the ultraviolet from 68 to 210 nm. It is primarily used to observe emission from the Jovian aurorae but is also sensitive to other sources, such as UV-bright stars, sky background Lyman-alpha emission, and reflected sunlight. However, Juno-UVS is also sensitive to the effects of penetrating high-energy radiation, which results in elevated count rates as measured by the instrument detector array. This radiation presents a challenge for efficiently planning the acquisition of mission science data, as data volume is a valuable (and finite) resource that can quickly be filled when the spacecraft periodically passes through regions of high radiation. This background radiation has been found to vary significantly on both short (spacecraft spin-modulated) timescales, as well as longer timescales from minutes to hours during each close approach to Jupiter. This variability has required a multipronged approach in the operation planning of hardware (such as, dynamic instrument voltage adjustment) as well as onboard software (such as, utilizing data quality factors for the selective storage of science data). We present an overview of these current mitigation/optimization techniques and planning strategies used for this instrument, which will likely also be useful for the development and operations of future instruments within high radiation space environments (e.g., the ESA JUICE mission or NASA’s Europa Clipper).

The ultraviolet spectrograph instrument on the Juno mission (Juno-UVS) is a long-slit imaging spectrograph designed to observe and characterize Jupiter’s far-ultraviolet (FUV) auroral emissions. These observations will be coordinated and correlated with those from Juno’s other remote sensing instruments and used to place in situ measurements made by Juno’s particles and fields instruments into a global context, relating the local data with events occurring in more distant regions of Jupiter’s magnetosphere. Juno-UVS is based on a series of imaging FUV spectrographs currently in flight—the two Alice instruments on the Rosetta and New Horizons missions, and the Lyman Alpha Mapping Project on the Lunar Reconnaissance Orbiter mission. However, Juno-UVS has several important modifications, including (1) a scan mirror (for targeting specific auroral features), (2) extensive shielding (for mitigation of electronics and data quality degradation by energetic particles), and (3) a cross delay line microchannel plate detector (for both faster photon counting and improved spatial resolution). This paper describes the science objectives, design, and initial performance of the Juno-UVS.

Watering the Moon About a year ago, a spent upper stage of an Atlas rocket was deliberately crashed into a crater at the south pole of the Moon, ejecting a plume of debris, dust, and vapor. The goal of this event, the Lunar Crater Observation and Sensing Satellite (LCROSS) experiment, was to search for water and other volatiles in the soil of one of the coldest places on the Moon: the permanently shadowed region within the Cabeus crater. Using ultraviolet, visible, and near-infrared spectroscopy data from accompanying craft, Colaprete et al. (p. 463 ; see the news story by Kerr ; see the cover) found evidence for the presence of water and other volatiles within the ejecta cloud. Schultz et al. (p. 468 ) monitored the different stages of the impact and the resulting plume. Gladstone et al. (p. 472 ), using an ultraviolet spectrograph onboard the Lunar Reconnaissance Orbiter (LRO), detected H 2 , CO, Ca, Hg, and Mg in the impact plume, and Hayne et al. (p. 477 ) measured the thermal signature of the impact and discovered that it had heated a 30 to 200 square-meter region from ∼40 kelvin to at least 950 kelvin. Paige et al. (p. 479) mapped cryogenic zones predictive of volatile entrapment, and Mitrofanov et al. (p. 483 ) used LRO instruments to confirm that surface temperatures in the south polar region persist even in sunlight. In all, about 155 kilograms of water vapor was emitted during the impact; meanwhile, the LRO continues to orbit the Moon, sending back a stream of data to help us understand the evolution of its complex surface structures.

The Lyman Alpha Mapping Project (LAMP) is a far-ultraviolet (FUV) imaging spectrograph on NASA’s Lunar Reconnaissance Orbiter (LRO) mission. Its main objectives are to (i) identify and localize exposed water frost in permanently shadowed regions (PSRs), (ii) characterize landforms and albedos in PSRs, (iii) demonstrate the feasibility of using natural starlight and sky-glow illumination for future lunar surface mission applications, and (iv) characterize the lunar atmosphere and its variability. As a byproduct, LAMP will map a large fraction of the Moon at FUV wavelengths, allowing new studies of the microphysical and reflectance properties of the regolith. The LAMP FUV spectrograph will accomplish these objectives by measuring the signal reflected from the night-side lunar surface and in PSRs using both the interplanetary HI Lyman-α sky-glow and FUV starlight as light sources. Both these light sources provide fairly uniform, but faint, illumination. With the expected LAMP sensitivity, by the end of the primary 1-year LRO mission, the SNR for a Lyman-α albedo map should be >100 in polar regions >1 km2, providing useful FUV constraints to help characterize subtle compositional and structural features. The LAMP instrument is based on the flight-proven Alice series of spectrographs flying on the Rosetta comet mission and the New Horizons Pluto mission. A general description of the LAMP instrument and its initial ground calibration results are presented here.

The New Horizons ALICE instrument is a lightweight (4.4 kg), low-power (4.4 Watt) imaging spectrograph aboard the New Horizons mission to Pluto/Charon and the Kuiper Belt. Its primary job is to determine the relative abundances of various species in Pluto's atmosphere. ALICE will also be used to search for an atmosphere around Pluto's moon, Charon, as well as the Kuiper Belt Objects (KBOs) that New Horizons hopes to fly by after Pluto-Charon, and it will make UV surface reflectivity measurements of all of these bodies as well. The instrument incorporates an off-axis telescope feeding a Rowland-circle spectrograph with a 520-1870 angstroms spectral passband, a spectral point spread function of 3-6 angstroms FWHM, and an instantaneous spatial field-of-view that is 6 degrees long. Different input apertures that feed the telescope allow for both airglow and solar occultation observations during the mission. The focal plane detector is an imaging microchannel plate (MCP) double delay-line detector with dual solar-blind opaque photocathodes (KBr and CsI) and a focal surface that matches the instrument's 15-cm diameter Rowland-circle. In what follows, we describe the instrument in greater detail, including descriptions of its ground calibration and initial in flight performance., Comment: 24 pages, 29 figures, 2 tables; To appear in a special volume of Space Science Reviews on the New Horizons mission

Four compact planetary ultraviolet spectrographs have been built by Southwest Research Institute and successfully operated on different planetary missions. These spectrographs underwent a series of ground radiometric calibrations before delivery to their respective spacecraft. In three of the four cases, the in-flight measured sensitivity was approximately 50% lower than the ground measurement. Recent tests in the Southwest Research Institute Ultraviolet Radiometric Calibration Facility (UV-RCF) explain the discrepancy between ground and flight results. Revised ground calibration results are presented for the Rosetta-Alice, New Horizons-Alice, the Lunar Reconnaissance Orbiter Lyman- Alpha Mapping Project, and Juno-Ultraviolet Spectrograph (UVS) and are then compared to the original ground and flight calibrations. The improved understanding of the calibration system reported here will result in improved ground calibration of the upcoming Jupiter Icy Moons Explorer (JUICE)-UVS.

[1] We present an analysis of Lunar Reconnaissance Orbiter (LRO) Lyman Alpha Mapping Project (LAMP) measurements of the dayside lunar surface at far-ultraviolet wavelengths. We use the strong 165 nm H2O absorption edge to look for diurnal variations in hydration. We find that diurnal variations in spectral slope are indeed present; they are superimposed on latitudinal and spatial variations related to composition and weathering. We use two different spectral regions (164–173 nm and 175–190 nm) to separate out these effects. Highlands and mare regions have distinct reflectance spectra, with mare regions being spectrally bluer than highlands regions, a consequence of the greater abundance of opaque minerals in mare regions. Bright ray terrains and areas known to be young such as Giordano Bruno crater, are found to be relatively spectrally flat or red in the far-UV; this is consistent with a lack of space weathering, which tends to make the far-UV spectrum bluer due to the spectral behavior of nanophase iron. Large-scale latitudinal variations in FUV slope are distinct and are likely due to a gradient in space weathering. The diurnal variation in hydration is consistent with a solar wind origin and with loss of H2O at temperatures above ∼320 K. Far-UV spectroscopy is thus shown to represent a viable method for mapping aqueous alteration, even on the dayside of the Moon, and potentially elsewhere in the solar system.

[1] Using a Monte Carlo model, we analyze the evolution of the vapor plume emanating from the Lunar Crater Observation and Sensing Satellite (LCROSS) impact into Cabeus as seen by the Lyman Alpha Mapping Project (LAMP), a far-ultraviolet (FUV) imaging spectrograph onboard the Lunar Reconnaissance Orbiter. The best fit to the data utilizes a bulk velocity between 3.0 and 4.0 km/s. The fits to the light curve comprised of Hg, Ca, and Mg are not strongly dependent on the temperature. In contrast, the best fit to the light curve from H2 and CO corresponds to a 500 K thermal velocity distribution. The LAMP field of view primarily encounters particles released at low angles to the horizontal and misses fast moving particles released at more vertical angles. The isotropic model suggests that 117 ± 16 kg H2, 41 ± 3 kg CO, 16 ± 1 kg Ca, 12.4 ± 0.8 kg Hg, and 3.8 ± 0.3 kg Mg are released by the LCROSS impact. Additional errors could arise from an anisotropic plume, which cannot be distinguished with LAMP data. Mg and Ca are likely incompletely volatilized owing to their high vapor temperatures. The highly volatile components (H2 and CO) might derive from a greater mass of material. To agree with predicted abundances by weight of 0.047%, 0.023%, 11%, 0.28% and 3.4% for H2, CO, Ca, Hg, and Mg, respectively, the species would be released from 250,000 kg, 180,000 kg, 140 kg, 4400 kg, and 110 kg of regolith, respectively. This is consistent with the relative volatility of these species.

We report observations of the lunar helium exosphere made between December 29, 2011, and January 26, 2012, with the Lyman Alpha Mapping Project (LAMP) ultraviolet spectrograph on NASA's Lunar Reconnaissance Orbiter Mission (LRO). The observations were made of resonantly scattered He I 584 from illuminated atmosphere against the dark lunar surface on the dawn side of the terminator. We find no or little variation of the derived surface He density with latitude but day-to-day variations that likely reflect variations in the solar wind alpha flux. The 5-day passage of the Moon through the Earth's magnetotail results in a factor of two decrease in surface density, which is well explained by model simulations., Comment: 21 pages, 5 figures, 3 supplementary figures, accepted for publication in Icarus

We describe the radiometric performance and ground calibration results of the Juno mission's Ultraviolet Spectrograph (Juno-UVS) flight model. Juno-UVS is a modest power (9.0 W) ultraviolet spectrograph based on the Alice instruments now in flight aboard the European Space Agency's Rosetta spacecraft, NASA's New Horizons spacecraft, and the LAMP instrument aboard NASA's Lunar Reconnaissance Orbiter. Its primary job will be to characterize Jupiter's UV auroral emissions and relate them to in situ particle measurements.

The Lyman Alpha Mapping Project (LAMP) is a lightweight (6.1 kg), low-power (4.5 W), ultraviolet spectrograph based on the Alice instruments now in flight aboard the European Space Agency's Rosetta spacecraft and NASA's New Horizons spacecraft. Its primary job on NASA's Lunar Reconnaissance Orbiter (LRO) is to identify and localize exposed water frost in permanently shadowed regions (PSRs) near the Moon's poles, and to characterize landforms and albedos in PSRs. In this paper we describe the in-flight radiometric performance and commissioning results and compare them to ground calibration measurements.

The European Space Agency's Rosetta spacecraft, en route to a 2014 encounter with comet 67P/Churyumov-Gerasimenko, made a gravity assist swing-by of Mars on 25 February 2007, closest approach being at 01:54UT. The Alice instrument on board Rosetta, a lightweight far-ultraviolet imaging spectrograph optimized for in situ cometary spectroscopy in the 750-2000 A spectral band, was used to study the daytime Mars upper atmosphere including emissions from exospheric hydrogen and oxygen. Offset pointing, obtained five hours before closest approach, enabled us to detect and map the HI Lyman-alpha and Lyman-beta emissions from exospheric hydrogen out beyond 30,000 km from the planet's center. These data are fit with a Chamberlain exospheric model from which we derive the hydrogen density at the 200 km exobase and the H escape flux. The results are comparable to those found from the the Ultraviolet Spectrometer experiment on the Mariner 6 and 7 fly-bys of Mars in 1969. Atomic oxygen emission at 1304 A is detected at altitudes of 400 to 1000 km above the limb during limb scans shortly after closest approach. However, the derived oxygen scale height is not consistent with recent models of oxygen escape based on the production of suprathermal oxygen atoms by the dissociative recombination of O2+., Comment: 17 pages, 8 figures, accepted for publication in Icarus

International audience; During Rosetta's flyby of the asteroid (2867) Šteins in 2008, we used the ALICE instrument to measure the first far-ultraviolet (FUV) reflectivity spectrum of an asteroid (850-2000 Å). It is very dark in the FUV, ~4%, compared to its very high reflectivity (40%) at optical wavelengths. The FUV albedo does not exhibit a systematic color trend across the spectral range, but there is a broad absorption feature, not yet identified with a specific mineral, with maximum depth near 1650 Å. The shape of this feature implies a very low abundance of Fe2+ ions in the surface minerals. The FUV brightness exhibits a significant opposition surge at phases below 10°. The visible/FUV color gets much redder with increasing phase angle inside the opposition surge and gets gradually redder at larger phase angles. We also conducted a deep search for an exosphere of atoms sputtered from the surface and set upper limits on any column densities of oxygen and hydrogen atoms at the time of our observations. The upper limit for H is comparable to that predicted by the only theoretical prediction of which we are aware, while that for O is higher than predicted by about an order of magnitude.

We describe the pre-flight radiometric performance and calibration results of the Lunar Reconnaissance Orbiter's Lyman Alpha Mapping Project (LRO/LAMP) flight model. LAMP is a lightweight (6.1 kg), low-power (4.5 W), ultraviolet spectrograph based on the ALICE instruments now in flight aboard the European Space Agency's Rosetta spacecraft and NASA's New Horizons spacecraft. Its primary job will be to identify and localize exposed water frost in permanently shadowed regions (PSRs), and to characterize landforms and albedos in PSRs. Detailed radiometric performance results of the LAMP flight model are presented and discussed.

Southwest Research Institute's (SwRI's) "ALICE" line of ultraviolet spectrographs (UVS) is founded on a lightweight, low power, and highly versatile instrument design. Generally small changes in detector photocathode, pixel size, slit shape, optical coatings, pinhole aperture implementations, and other minor tweaks have enabled a wide variety of applications for the ALICE design, including investigations of comets (Rosetta-ALICE), Pluto (New Horizons-ALICE), the Moon (Lunar Reconnaissance Orbiter (LRO)-Lyman Alpha Mapping Project (LAMP)), and Jupiter (Juno-UVS). ALICE's high capability and our experience with high radiation environment and outer solar system requirements make this UVS a good choice for future planetary mission concepts.

Observations of Jupiter's nightside airglow (nightglow) and aurora obtained during the flyby of the New Horizons spacecraft show an unexpected lack of ultraviolet nightglow emissions, in contrast to the case during the Voyager flybys in 1979. The flux and average energy of precipitating electrons generally decrease with increasing local time across the nightside, consistent with a possible source region along the dusk flank of Jupiter's magnetosphere. Visible emissions associated with the interaction of Jupiter and its satellite Io extend to a surprisingly high altitude, indicating localized low-energy electron precipitation. These results indicate that the interaction between Jupiter's upper atmosphere and near-space environment is variable and poorly understood; extensive observations of the day side are no guide to what goes on at night.