High-Resolution Spectroscopy of Auroras on Jupiter and Saturn/Earth Dayglow

The purpose of the grant was to allow the researcher to: (1) reduce and analyze Orbiting and Retrievable Far and Extreme Ultraviolet Spectrometers (ORFEUS) II observations of Jupiter (200s) and Saturn (1200s); (2) Reduce and analyze selected ORFEUS-II Earth Far Ultraviolet (FUV) airglow data; (3) Modify existing scripts for simulating Earth FUV airglow emissions to model a subset of the ORFEUS data

An analysis of the reflection spectrum of Jupiter from 1500 Å to 1740 Å

A study is made of the UV reflection spectrum of Jupiter as measured by the International Ultraviolet Explorer. Detailed modeling reveals the mixing ratios of C_2H_2, C_2H_6, and C_4H_2 to be (1.0 ± 0.1) x 10^(-1), (6.6 ± 5.3) x 10^(-6), and (2.9 ± 2.0) x 10^(-10), respectively, in the pressure region between ~3 and 40 mbar. Upper limits in this pressure region for the mixing ratios of C_2H_4 and NH_3 were determined to be (3.9^(+4.9)_(-3.9))x10^(-10) and (4.2^(+6.7)_(-4.2))x10^(-9), respectively. An upper limit to the optical depth of dust above the tropopause, assuming it is well mixed, is 0.2^(+0.3)_(-1.4), and an upper limit on the dayglow emission by the Lyman bands of H_2 is 1.4^(+2.4)_(-1.4) kR. Comparison with Voyager results suggests that the scale height of C_2H_2 in the region 150-10 mbar is approximately twice that of the bulk atmosphere, consistent with the IUE observation of cosine-like limb darkening in the north-south direction on Jupiter in this spectral range. These results are of use in the photochemical modeling of the upper atmosphere of Jupiter

Nitrogen and Oxygen Photochemistry following SL9

The collision of Shoemaker Levy 9 (SL9) with Jupiter caused many new molecular species to be deposited in the Jovian stratosphere. We use a photochemical model to follow the evolution of the impact derived species. Our results regarding the nitrogen and oxygen compounds are presented here. NH3 photolysis initiates the nitrogen photochemistry. Much of the nitrogen ends up in N2, nitrogen-sulfur compounds, and HCN, but NH3 and nitriles such as C2H3CN may also exist in observable quantities for a year or so after the impacts. Oxygen species survive for a long time in the Jovian stratosphere. The only major oxygen containing compounds that exhibit dramatic changes in the lower stratosphere in the first year following the impacts are SO, SO2, and OCS - H2O, CO2, and CO are comparatively stable. We discuss the important photochemical processes operating on the nitrogen and oxygen species in the Jovian stratosphere, make prediction concerning the temporal variation of the major species, and identify molecules that might act as good tracers for atmospheric dynamics

The atmosphere of Pluto as observed by New Horizons

In July 2015, the New Horizons spacecraft flew through the Pluto system at high speed, humanity's first close look at this enigmatic system on the outskirts of our solar system. In a series of papers, the New Horizons team present their analysis of the encounter data downloaded so far: Moore et al. present the complex surface features and geology of Pluto and its large moon Charon, including evidence of tectonics, glacial flow, and possible cryovolcanoes. Grundy et al. analyzed the colors and chemical compositions of their surfaces, with ices of H_2O, CH_4, CO, N_2, and NH_3 and a reddish material which may be tholins. Gladstone et al. investigated the atmosphere of Pluto, which is colder and more compact than expected and hosts numerous extensive layers of haze. Weaver et al. examined the small moons Styx, Nix, Kerberos, and Hydra, which are irregularly shaped, fast-rotating, and have bright surfaces. Bagenal et al. report how Pluto modifies its space environment, including interactions with the solar wind and a lack of dust in the system. Together, these findings massively increase our understanding of the bodies in the outer solar system. They will underpin the analysis of New Horizons data, which will continue for years to come

Chandra Observation of an X-ray Flare at Saturn: Evidence for Direct Solar Control on Saturn's Disk X-ray Emissions

Saturn was observed by Chandra ACIS-S on 20 and 26-27 January 2004 for one full Saturn rotation (10.7 hr) at each epoch. We report here the first observation of an X-ray flare from Saturn's non-auroral (low-latitude) disk, which is seen in direct response to an M6-class flare emanating from a sunspot that was clearly visible from both Saturn and Earth. Saturn's disk X-ray emissions are found to be variable on time scales of hours to weeks to months, and correlated with solar F10.7 cm flux. Unlike Jupiter, X-rays from Saturn's polar (auroral) region have characteristics similar to those from its disk. This report, combined with earlier studies, establishes that disk X-ray emissions of the giant planets Saturn and Jupiter are directly regulated by processes happening on the Sun. We suggest that these emissions could be monitored to study X-ray flaring from solar active regions when they are on the far side and not visible to Near-Earth space weather satellites.Comment: Total 12 pages including 4 figure

H_2 fluorescence spectrum from 1200 to 1700 Å by electron impact: Laboratory study and application to Jovian aurora

A combined experimental study of the fluorescence spectrum of H_2 at wavelengths of 1200-1700 Å by electron impact and its application to modeling the Jovian aurora have been carried out. Our laboratory data suggest that at 100 eV the relative cross sections for direct excitation of Lyɑ, Lyman bands (B^1Σ_u^+-X^1Σ_g^+), and Werner bands (C^1π_u-X^1Σ_g^+) are 1, 2.3±0.6, and 2.6±0.5, respectively, in conflict with Stone and Zipfs (1972) results for the Werner bands. Cascade from E,F^1Σ_g^+ states contributes an additional 31% to the B^1Σ_u^+ state population. It is shown that the most likely fate for the metastable H(2^2S) atoms produced in the Jovian aurora is collisional quenching to H(2^2P), and this could add as much as 60% to the predicted Lyɑ emission. On the basis of detailed atmospheric and radiative transfer modeling, we conclude that the recent IUE and Voyager observations are consistent with precipitation of electrons with energy in the range of 1-30 keV or other energetic particles that penetrate to number densities of 4 X 10^(10)-5 X 10^(13) cm^(-3) or column densities of 5 X 10^(17)-2 X 10^(20) cm^(-2) in the atmosphere. The globally averaged energy flux and production of hydrogen atoms are 0.5-2 ergs cm^(-2) s^(-1) and 1-4 X 10^(10) atoms cm^(-2) s^(-1), respectively

The crucial role of HST during the NASA Juno mission: a "Juno initiative"

In 2016, the NASA Juno spacecraft will initiate its one-year mission around Jupiter and become the first probe to explore the polar regions of Jupiter. The HST UV instruments (STIS and ACS) can greatly contribute to the success of the Juno mission by providing key complementary views of Jupiter's UV aurora from Earth orbit. Juno carries an ultraviolet Spectrograph (UVS) and an infrared spectral mapper (JIRAM) that will obtain high-resolution spectral images providing the auroral counterpart to Juno's in situ particles and fields measurements with the plasma JADE and JEDI particle detectors. The Juno mission will be the first opportunity to measure simultaneously the energetic particles at high latitude and the auroral emissions they produce. Following programmatic and technical limitations, the amount of UVS data transmitted to Earth will be severely restricted. Therefore, it is of extreme importance that HST captures as much additional information as possible on Jupiter's UV aurora during the one-year life of the Juno mission. This white paper is a plea for a "Juno initiative" that will ensure that a sufficient number of orbits is allocated to this unique solar system mission.Comment: Paper submitted to the Space Telescope Science Institute in response to the call for HST White Papers for Hubble's 2020 Visio

Two-Dimensional Distribution of Volatiles in the Lunar Regolith from Space Weathering Simulations

We present simulations of space weathering effects on ice deposits in regions of permanent shadow on the Moon. These Monte Carlo simulations follow the effects of space weathering processes on the distribution of the volatiles over time. The model output constrains the coherence of volatile deposits with depth, lateral separation, and time. The results suggest that ice sheets become broken and buried with time. As impacts begin to puncture an initially coherent surficial ice sheet, small areas with a deficit of ice compared to surrounding areas are formed first. As time progresses, holes become prevalent and the anomalous regions are local enhancements of ice concentration in a volume. The 3-D distribution is also heterogeneous because the ice is buried to varying depths in different locations. Analysis of the coherence of ice on 10 cm scales predicts that putative ice sheets in anomalous radar craters are 1000 Myr old. For future in situ analysis of cold trap volatiles, a horizontal range of 10 m is sufficient to acquire surface-based measurements of heterogeneously distributed ice. These results also support previous analyses that Mercury's cold traps are young

Discovery of Oxygen Kalpha X-ray Emission from the Rings of Saturn

Using the Advanced CCD Imaging Spectrometer (ACIS), the Chandra X-ray Observatory (CXO) observed the Saturnian system for one rotation of the planet (~37 ks) on 20 January, 2004, and again on 26-27 January, 2004. In this letter we report the detection of X-ray emission from the rings of Saturn. The X-ray spectrum from the rings is dominated by emission in a narrow (~130 eV wide) energy band centered on the atomic oxygen K-alpha fluorescence line at 0.53 keV. The X-ray power emitted from the rings in the 0.49-0.62 keV band is 84 MW, which is about one-third of that emitted from Saturn disk in the photon energy range 0.24-2.0 keV. Our analysis also finds a clear detection of X-ray emission from the rings in the 0.49-0.62 keV band in an earlier (14-15 April, 2003) Chandra ACIS observation of Saturn. Fluorescent scattering of solar X-rays from oxygen atoms in the H2O icy ring material is the likely source mechanism for ring X-rays, consistent with the scenario of solar photo-production of a tenuous ring oxygen atmosphere and ionosphere recently discovered by Cassini.Comment: 14 pages, 5 figures Astrophys. J Lett., in pres