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In this work we present the results of a spectral observing campaign of Pluto to search for temporal changes in surface composition on 1- to 3-year timescales. Near-infrared spectra of Pluto were obtained from June 2014 to August 2017 with the TripleSpec cross-dispersed spectrograph at the Apache Point Observatory's 3.5-meter Astrophysical Research Consortium (ARC) telescope. Observations were requested in order to obtain spectra of approximately the same sub-observer hemisphere $\sim$14 months apart, thus removing the effects of viewing geometry and rotation phase. Comparison of the CH$_4$ (methane) band areas and band center shifts between each component of these "matched pairs" revealed a surface in transition. Band areas for the 1.66 and 1.72 $\mu$m CH$_4$ absorption features exhibited a $>$5-$\sigma$ increase between 2014-06-17 and 2015-08-19, corresponding to a sub-observer hemisphere centered at $\sim$280$^{\circ}$E, with the latter date only 1 month after the New Horizons flyby of Pluto. The majority of matched pairs were obtained of the anti-Charon hemisphere, home to the bright, volatile-rich Sputnik Planitia, and did not present statistically significant changes in CH$_4$ band areas. CH$_4$ band center shifts, which provide information on the mixing state of CH$_4$ and N$_2$ in solid solution, were calculated between components of each matched pair, with no significant band shifts detected. The favored explanation for these combined results is the sublimation of more-volatile N$_2$ from the northern latitudes of Pluto in the lead-up to northern hemisphere summer solstice in 2029, leading to an increase in CH$_4$ concentration., Comment: 28 pages, 8 figures, 5 tables

Here we present new ultraviolet–visible spectra of irradiated ammonium hydrosulfide (NH4SH), a reported jovian atmospheric cloud component, for a range of temperatures and radiation doses and make assignments to the spectral features. We show that the combination of radiolysis and thermal annealing of NH4SH causes the originally featureless ultraviolet–visible reflectance spectrum to evolve into one that absorbs in the ultraviolet–visible region. Furthermore, we find that our laboratory spectra resemble HST spectra below 500 nm, suggesting that the more stable reaction products of NH4SH radiolysis are likely an important component of the Great Red Spot.

We present analysis of high spectral resolution NIR spectra of CO and H$_2$O in comet C/2009 P1 (Garradd) taken during its 2011-2012 apparition with the CSHELL instrument on NASA's Infrared Telescope Facility (IRTF). We also present analysis of observations of atomic oxygen in comet Garradd obtained with the ARCES echelle spectrometer mounted on the ARC 3.5-meter telescope at Apache Point Observatory and the Tull Coude spectrograph on the Harlan J. Smith 2.7-meter telescope at McDonald Observatory. The observations of atomic oxygen serve as a proxy for H$_2$O and CO$_2$. We confirm the high CO abundance in comet Garradd and the asymmetry in the CO/H$_2$O ratio with respect to perihelion reported by previous studies. From the oxygen observations, we infer that the CO$_2$/H$_2$O ratio decreased as the comet moved towards the Sun, which is expected based on current sublimation models. We also infer that the CO$_2$/H$_2$O ratio was higher pre-perihelion than post-perihelion. We observe evidence for the icy grain source of H$_2$O reported by several studies pre-perihelion, and argue that this source is significantly less abundant post-perihelion. Since H$_2$O, CO$_2$, and CO are the primary ices in comets, they drive the activity. We use our measurements of these important volatiles in an attempt to explain the evolution of Garradd's activity over the apparition., 35 pages, 10 figures, 9 tables, accepted for publication in Icarus

We observed the Venusian 5577.3 A OI ( 1 S– 1 D) (oxygen green line) nightglow emission feature after solar flares, coronal mass ejections (CMEs), and solar wind streams from December 2010 to July 2012 using the high resolution Astrophysical Research Consortium Echelle Spectrograph on the Apache Point Observatory 3.5 m telescope. For the first time since 2004, we detected the green line. The emission is highly temporally variable, with the strongest emission detected being comparable to the previously known brightest detection, and to occur after each of the three types of solar events. We find the greatest emission occurs after CMEs and suggest that particle precipitation is the main contributor to green line emission.

We extracted physical atmospheric parameters from a 23 July 2008 single-chord stellar occultation of the star USNO-B1.0 0759-0739128 (I-band magnitude of 12.60) by Neptune using a light curve model fitting technique. We observed the occultation using the Agile CCD camera mounted on the Astrophysical Research Consortium 3.5 m telescope at Apache Point Observatory. We found isothermal temperatures of 116.5 ± 12.0 K and 154.0 ± 13.0 K for the immersion and emersion light curve profiles, respectively. We compare the stratospheric temperatures derived from the 2008 occultation to published temperatures of Neptune at similar atmospheric pressures derived from previous stellar occultations observed in the 1980s, and from long-term photometric measurements made routinely since the 1983–1990 occultation campaign. No obvious long-term temporal variation in stratospheric isothermal temperature is present. Fluctuations in the fitted isothermal temperature values, on the order of 20 K, is evident. We explore several hypotheses to explain the observed temperature variability of Neptune’s stratosphere, including seasonal variability, variations in the Lyman- α flux received at Neptune due to the 11-year solar cycle, diurnal variations, varying insolation due to heliocentric variability, IR and UV heating by hydrocarbons, aerosol precipitation, inertia-gravity wave dissipation, and effects due to atmospheric tidal perturbations by Triton. We investigate the effects of these mechanisms on the gradual temporal changes of Neptune’s stratospheric temperature and conclude that local variations in stratospheric temperature during each event, on the order of 20 K, are dominated by viscous dissipation of inertia-gravity waves.

We present analysis of high spectral resolution optical spectra of Comet 103P/Hartley taken during its Fall 2010 apparition. These spectra include transitions belonging to CN, C2, CH, NH2, and OI. We measure production rates and mixing ratios from these spectra. We find evidence for large changes in production rates (factors of a few) over the course of a nucleus rotation, in agreement with other measurements. We also measure variability with rotational phase in the CN/H2O and C2/CN ratios, which has not been previously reported for any comet. There may also be variability in the NH2/H2O ratio with rotational phase, but this trend is not as clear as for CN/H2O. We interpret the changing mixing ratios as due to H2O and C2 being released primarily from the icy grain halo, while the CN parent molecule comes directly from the nucleus. There is evidence that the CH/CN ratio is higher pre-perihelion than post-perihelion. We conclude that the observed CN and NH2 abundances are consistent with HCN and NH3 being the dominant parent molecules for these species. The C2 and CH abundances are higher than those of candidate parent molecules (C2H2 and CH4 respectively), so there must be another source for these molecules in 103P’s coma. Carbonaceous dust grains could serve as this source.

A superior mutual event of the Kuiper Belt binary system (79360) Sila-Nunam was observed over 15.47 h on UT 7/8 February 2013 by a coordinated effort at four different telescope facilities; it started approximately 1.5 h earlier than anticipated, the duration was approximately 9.5 h (about 10% longer than predicted), and was slightly less deep than predicted. It is the first full event observed for a comparably sized binary Kuiper Belt object. We provide predictions for future events refined by this and other partial mutual event observations obtained since the mutual event season began.

The oxygen green line is one of the most characteristic features in the terrestrial visible nightglow; it can be seen in the Venus nightglow, but with much greater intensity variation than in the terrestrial case. Here we synthesize our current understanding of the green line in the Venus nightglow and discuss what might be expected observationally in the rising phase of solar cycle 24.

The chromophores responsible for coloring the jovian atmosphere are embedded within Jupiter's vertical aerosol structure. Sunlight propagates through this vertical distribution of aerosol particles, whose colors are defined by omega-bar (sub 0)(lambda), and we remotely observe the culmination of the radiative transfer as I/F(lambda). In this study, we employed a radiative transfer code to retrieve omega-bar (sub 0)(lambda) for particles in Jupiter's tropospheric haze at seven wavelengths in the near-UV and visible regimes. The data consisted of images of the 2008 passage of Oval BA to the south of the Great Red Spot obtained by the Wide Field Planetary Camera 2 on-board the Hubble Space Telescope. We present derived particle colors for locations that were selected from 14 weather regions, which spanned a large range of observed colors. All omega-bar (sub 0)(lambda) curves were absorbing in the blue, and omega-bar (sub 0)(lambda) increased monotonically to approximately unity as wavelength increased. We found accurate fits to all omega-bar (sub 0)(lambda) curves using an empirically derived functional form: omega-bar (sub 0)(lambda) = 1 A exp(-B lambda). The best-fit parameters for the mean omega-bar (sub 0)(lambda) curve were A = 25.4 and B = 0.0149 for lambda in units of nm. We performed a principal component analysis (PCA) on our omega-bar (sub 0)(lambda) results and found that one or two independent chromophores were sufficient to produce the variations in omega-bar (sub 0)(lambda). A PCA of I/F(lambda) for the same jovian locations resulted in principal components (PCs) with roughly the same variances as the omega-bar (sub 0)(lambda) PCA, but they did not result in a one-to-one mapping of PC amplitudes between the omega-bar (sub 0)(lambda) PCA and I/F(lambda) PCA. We suggest that statistical analyses performed on I/ F(lambda) image cubes have limited applicability to the characterization of chromophores in the jovian atmosphere due to the sensitivity of 1/ F(lambda) to horizontal variations in the vertical aerosol distribution.

We observed Phoebe for 13 nights over a period of 55 days before, during, and after the 2005 Saturn opposition with the New Mexico State University (NMSU) 1-m telescope at Apache Point Observatory (APO) in Sunspot, NM and characterized the width and magnitude of Phoebe’s opposition surge in BVRI filters. Our observations cover a phase angle range of 4.87° to 0.0509°. We use a Hapke reflectance model incorporating shadow hiding and coherent backscatter to investigate the wavelength dependence of Phoebe’s opposition surge. We find a significant opposition surge magnitude of 55–58% between phase angles of 5° and 0°. We find the strongest opposition surge for phase angles less than 2° in the I-band. The coherent backscatter angular width is on the order of 0.50°. We find Phoebe’s albedo to be spectrally flat within our error limits, with a B-band albedo of 0.0855 ± 0.0031, a V-band albedo of 0.0856 ± 0.0023, an R-band albedo of 0.0843 ± 0.0020, and an I-band albedo of 0.0839 ± 0.0023. We compare Phoebe’s albedo, color, and opposition surge magnitudes and slopes with those of other outer solar system bodies and find similarities to Centaurs, Nereid, Puck, and Comets 19P/Borrelly, 9P/Tempel 1, and 81P/Wild 2. We find that this comparison supports the idea that Phoebe originated in the Kuiper Belt. We also discuss the caveats of using results from a Hapke reflectance model to derive specific surface particle properties.

We present a novel method of constructing streamlines to derive wind speeds within jovian vortices and demonstrate its application to Oval BA for 2001 pre-reddened Cassini flyby data, 2007 post-reddened New Horizons flyby data, and 1998 Galileo data of precursor Oval DE. Our method, while automated, attempts to combine the advantages of both automated and manual cloud tracking methods. The southern maximum wind speed of Oval BA does not show significant changes between these data sets to within our measurement uncertainty. The northern maximum dries appear to have increased in strength during this time interval, tvhich likely correlates with the oval's return to a symmetric shape. We demonstrate how the use of closed streamlines can provide measurements of vorticity averaged over the encircled area with no a priori assumptions concerning oval shape. We find increased averaged interior vorticity between pre- and post-reddened Oval BA, with the precursor Oval DE occupying a middle value of vorticity between these two.

We obtained near-infrared spectra of Uranus at NASA’s Infrared Telescope Facility during the planet’s September 2006 and September 2007 oppositions. Ratios between the spectra indicate that in 2006, Uranus’ methane windows appeared much brighter in the south than in the north, and that between 2006 and 2007 they grew dimmer in the south and brighter in the north; we interpret these variations to be primarily caused by changing brightness in Uranus’ upper cloud layer near 2 bars.

We observed the 15 August 2007 occultation of the uranian satellite Titania and the 19 August 2007 occultation of Ariel by Umbriel using the Agile high-speed photometer on the APO 3.5 m telescope. We find that the Titania event midpoint occurred at 09:16:39.20 UT and the Ariel event midpoint at 07:59:49.4 UT, which was 26.2 s and 37.4 s later than predicted, respectively. Our best fit impact parameter was 71.0 km for the Titania occultation and 476.9 km for the Ariel event, both of which were less than predicted.

We report on the analysis of high spatial resolution visible to near-infrared spectral images of Titan at Ls=240°Ls=240° in November 2000, obtained with the Space Telescope Imaging Spectrograph instrument on board the Hubble Space Telescope as part of program GO-8580. We employ a radiative transfer fractal particle aerosol model with a Bayesian parameter estimation routine that computes Titan's absolute reflectivity per pixel for 122 wavelengths by modeling the vertical distribution of the lower atmosphere haze and tropospheric methane. Analysis of these data suggests that Titan's haze concentration in the lower atmosphere varies in strength with latitude. We find Titan's tropospheric methane profile to be fairly consistent with latitude and longitude, and we find evidence for local areas of a CH4–N2 binary saturation in Titan's troposphere. Our results suggest that a methane and haze profile at one location on Titan would not be representative of global conditions.

Jupiter's remaining White Oval changed color in late 2005 and became noticeably red in early 2006, as reported by amateur observers. We present wind and color analyses from high spatial resolution images taken with the Hubble Space Telescope Advanced Camera for Surveys in April 2006. These images suggest that the recent color change was tied to a strengthening of this storm, as implied by increased vorticity, causing it to become more like the Great Red Spot. From a historical perspective, the current activity may be consistent with the generation of new anticyclones at this latitude in the coming months and years.

In 1999, observations of the Venus nightglow with the Keck I telescope showed that the 5577 A oxygen green line was a significant feature, comparable in intensity to the terrestrial green line. Subsequent measurements have been carried out at the Apache Point Observatory (APO) and again at Keck I, confirming the presence of the line with substantially varying intensity. The Herzberg II emission intensity, from the O2( c – X ) transition, was found to have an intensity near 3 kR in one APO run, comparable to the value found on all previous measurements. Thus, of the three oxygen features seen at Venus—the green line, the Herzberg II emission system, and the 1.27-μ 0–0 band of the IR atmospheric system—the first is quite variable, the second is relatively constant, while the third also shows large variations. The reaction between O2( c 1 Σ u − , v = 0 ) and CO is considered as a possible mechanism to explain green line production and its variability, as well as the variability of the 1.27-μ emission and the stability of the CO2 atmosphere. This reaction may catalyze CO2 recombination some five orders of magnitude faster than the slow three-body O + CO reaction.

High spatial resolution images of Mars were acquired with the Advanced Electro-Optical System (AEOS) 3.63-meter telescope at the Maui Space Surveillance System (MSSS) during both the 2001 and 2003 Mars apparitions. Comparisons are made of the surface albedo patterns obtained from these AEOS images to the surface albedo maps constructed from the Mars Global Surveyor (MGS) Thermal Emission Spectrometer (TES) data taken during the same time periods. These comparisons demonstrate that the images provide albedo information in a limited area surrounding the sub-Earth point that is consistent with the TES-derived albedo field. Additionally, it is shown that by employing adaptive optics (AO), the typical ground-based observing season of Mars can be extended. This is the only known published AO data set of Mars with temporal coverage over an entire apparition. Changes in the surface albedo affect the local ground temperature, which impacts the depth of the planetary boundary layer (PBL) above the surface. Since it is the state of the PBL that controls surface/atmospheric interaction, albedo variations have the power to alter the amount of dust that is lifted. A one-dimensional radiative/convective version of the NASA Ames Mars General Circulation Model is used to demonstrate that the measured albedo variations can alter the daytime ground temperatures by as much as 5 K, which in turn alters the structure of the planetary boundary layer (PBL). Therefore, albedo changes are thermodynamically important, and the ability to characterize them, should orbital observations become unavailable, is a valuable capability.

Narrow-band images of Titan were obtained in November 1999 with the NASA/GSFC- built acousto-optic imaging spectrometer (AImS) camera. This instrument utilizes a tunable filter element that was used within the 500- to 1050-nm range, coupled to a CCD camera system. The images were taken with the Mount Wilson 2.54-m (100 in.) Hooker telescope, which is equipped with a natural guide star adaptive optics system. We observed Titan at 830 and 890 nm and at a series of wavelengths across the 940-nm window in Titan’s atmosphere where the methane opacity is relatively low. We determined the absolute reflectivity (I/F) of Titan and fit the values at 940 nm to a Minnaert function at Titan’s equator and at −30° latitude (closer to the subsolar point) and obtained average values for the Minnaert limb-darkening slope, k, of 0.661 ± 0.007 and 0.775 ± 0.018, respectively. Comparison with models suggests that the equatorial value of k is consistent with rain removal of haze in the lower atmosphere. The higher value of k at −30° is consistent with the southern hemisphere being brighter than the equator. However, the fits are not unique. The data and models at 890 are consistent with no limb brightening or darkening at this wavelength either at the equator or at −30°.

The vertical structure of Jupiter's atmosphere is examined to better characterize the latitudinal region of the Galileo probe entry site: +5°–10° planetographic latitude. One-hundred Hubble Space Telescope images of Jupiter taken with the 893- and 953-nm filters on 13 and 17 February 1995, 5 October 1995, and 14 May 1996 are analyzed, and a two-cloud model of the jovian atmosphere (D. M. Kuehn and R. F. Beebe 1993, Icarus 101, 282–292) is used to interpret center-to-limb variations of bright plume heads and adjacent dark areas in the latitude region +2°–10°. For both the plume heads and dark areas, the top of the ammonia cloud deck reaches a pressure level of roughly 200 mbar, and the cloud has an optical depth of between 6 and 7. The optical depth of the stratospheric haze layer is 0.59 for the plumes and 0.34 for the dark regions, while the single scattering albedo of the ammonia cloud deck is 0.996 for the plumes and 0.950 for the dark regions. Sensitivity tests motivated by the preliminary results from the Galileo probe net flux radiometer and nephelometer experiments indicate that the ammonia cloud deck may have a patchy structure.

The world-wide observing campaign of the Comet P/Shoemaker–Levy 9 (SL9) impacts into Jupiter during July 1994 has led to an unprecedented quantity of imaging data, predominantly in the visible to near-infrared wavelength regime. In an effort to provide reference brightness values for Jupiter at all latitudes, we present a compilation of absolute reflectivity scans along the jovian central meridian during the impact epoch. Images from both Earth-orbiting and ground-based telescopes were photometrically calibrated and analyzed to provide as much spatial resolution and wavelength coverage as possible. This fundamental reference will be made available to the entire planetary science community as a means to photometrically reduce uncalibrated data from the SL9 impacts via the Planetary Data System (PDS). Until the entire data set is ingested into the PDS, it will be available through a World Wide Web site and the AAS CD-ROM series.

Schmider et al. (Schmider, F.-X., B. Mosser, and E. Fossat 1991. Astron. Astrophy. 248, 281-291) and Mosser et al. (Mosser, B., D. Mekarnia, J.P. Maillard, J. Gay, D. Gautier, and P. Delache 1993. Astron. Astrophys. 267, 604-622) report detection of Doppler shifts in reflected solar radiation from Jupiter purportedly induced by p-mode oscillations of the planet. We consider the possibility that these observations may be recording quasi-periodic albedo features in Jupiter's atmosphere rather than or in addition to jovian oscillations. We model the Fourier Transform Spectroscopy method of p-mode detection in detail and employ near-IR methane-band images of Jupiter to test the albedo feature hypothesis. The low frequency portion (

The pole direction and radius scale for the ring system of Saturn are presently determined by combining the July 3, 1989 observations of 28 Sgr's occultation by Saturn with Voyager 1 and 2 photopolarimeter occultation measurements. The computation of ring-orbit models is separately conducted via a sky-plane method and a solar system barycentric vector approach; the results obtained by both methods are in excellent agreement. If Voyager trajectory uncertainties are assumed to be negligible, these observations can be used to determine the precession rate of the pole of Saturn about the solar system's invariable pole.