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On 2016 Feb 19, nine Rosetta instruments serendipitously observed an outburst of gas and dust from the nucleus of comet 67P/Churyumov-Gerasimenko. Among these instruments were cameras and spectrometers ranging from UV over visible to microwave wavelengths, in situ gas, dust and plasma instruments, and one dust collector. At 09:40 a dust cloud developed at the edge of an image in the shadowed region of the nucleus. Over the next two hours the instruments recorded a signature of the outburst that significantly exceeded the background. The enhancement ranged from 50 per cent of the neutral gas density at Rosetta to factors >100 of the brightness of the coma near the nucleus. Dust related phenomena (dust counts or brightness due to illuminated dust) showed the strongest enhancements (factors>10). However, even the electron density at Rosetta increased by a factor 3 and consequently the spacecraft potential changed from ~-16 V to -20 V during the outburst. A clear sequence of events was observed at the distance of Rosetta (34 km from the nucleus): within 15 min the Star Tracker camera detected fast particles (~25 m s-1) while 100 ¿m radius particles were detected by the GIADA dust instrument ~1 h later at a speed of 6 m s-1. The slowest were individual mm to cm sized grains observed by the OSIRIS cameras. Although the outburst originated just outside the FOV of the instruments, the source region and the magnitude of the outburst could be determined. © 2016 The Authors., Rosetta is an ESA mission with contributions from its member states and NASA. Rosetta's Philae lander is provided by a consortium led by DLR, MPS, CNES and ASI. We thank all elements of the Rosetta project for the magnificent job they are doing to make this mission an astounding success. The Alice team acknowledges continuing support from NASA's Jet Propulsion Laboratory through contract 1336850. GIADA/Univ Parthenope NA/INAFOAC/IAA/INAF-IAPS: this research was supported by the Italian Space Agency (ASI) within the ASI-INAF agreements I/032/05/0 and I/024/12/0. OSIRIS was built by a consortium of the Max-Planck- Institut für Sonnensystemforschung, Göttingen, Germany, CISAS University of Padova, Italy, the Laboratoire d'Astrophysique de Marseille, France, the Instituto de Astrofìsica de Andalucia, CSIC, Granada, Spain, the Research and Scientific Support Department of the European Space Agency, Noordwijk, The Netherlands, the Instituto Nacional de Técnica Aeroespacial, Madrid, Spain, the Universidad Politéechnica de Madrid, Spain, the Department of Physics and Astronomy of Uppsala University, Sweden, the UK(STFC), and the Institut für Datentechnik und Kommunikationsnetze der Technischen Universität Braunschweig, Germany. The support of the national funding agencies of Germany (DLR), France(CNES), Italy(ASI), Spain(MEC), Sweden(SNSB), and the ESA Technical Directorate is gratefully acknowledged. Work at LPC2E/CNRS was supported by CNES and by ANR under the financial agreement ANR-15-CE31-0009-01. Work on ROSINA COPS at the University of Bern was funded by the State of Bern, the Swiss National Science Foundation and by the European Space Agency PRODEX program. OM: this work has been partly carried out thanks to the support of the A*MIDEX project (no ANR-11-IDEX-0001-02) funded by the ‘Investissements d'Avenir’ French Government program, managed by the French National Research Agency (ANR). This work also benefited from the support of CNRS-INSU national program for planetology (PNP).

Thermal-infrared imaging of Jupiter and Saturn using the NASA/IRTF and Subaru observatories are quantitatively analyzed to assess the capabilities for reproducing and extending the zonal mean atmospheric results of the Cassini/CIRS experiment. We describe the development of a robust, systematic and reproducible approach to the acquisition and reduction of planetary images in the mid-infrared (7-25 μm), and perform an adaptation and validation of the optimal estimation, correlated-k retrieval algorithm described by Irwin et al. [Irwin, P., Teanby, N., de Kok, R., Fletcher, L., Howett, C., Tsang, C., Wilson, C., Calcutt, S., Nixon, C., Parrish, P., 2008. J. Quant. Spectrosc. Radiat. Trans. 109 (6), 1136-1150] for channel-integrated radiances. Synthetic spectral analyses and a comparison to Cassini results are used to verify our abilities to retrieve temperatures, haze opacities and gaseous abundances from filtered imaging. We find that ground-based imaging with a sufficiently high spatial resolution is able to reproduce the three-dimensional temperature and para-H2 fields measured by spacecraft visiting Jupiter and Saturn, allowing us to investigate vertical wind shear, pressure and, with measured cloud-top winds, Ertel potential vorticity on potential temperature surfaces. Furthermore, by scaling vertical profiles of NH3, PH3, haze opacity and hydrocarbons as free parameters during thermal retrievals, we can produce meridional results comparable with CIRS spectroscopic investigations. This paper demonstrates that mid-IR imaging instruments operating at ground-based observatories have access to several dynamical and chemical diagnostics of the atmospheric state of the gas giants, offering the prospect for quantitative studies over much longer baselines and often covering much wider areas than is possible from spaceborne platforms. © 2008 Elsevier Inc.

Near-infrared and mid-infrared observations of the site of the 2009 July 19 impact of an unknown object with Jupiter were obtained within days of the event. The observations were used to assess the properties of a particulate debris field, elevated temperatures, and the extent of ammonia gas redistributed from the troposphere into Jupiter's stratosphere. The impact strongly influenced the atmosphere in a central region, as well as having weaker effects in a separate field to its west, similar to the Comet Shoemaker-Levy 9 (SL9) impact sites in 1994. Temperatures were elevated by as much as 6K at pressures of about 50-70mbar in Jupiter's lower stratosphere near the center of the impact site, but no changes above the noise level (1K) were observed in the upper stratosphere at atmospheric pressures less than ∼1mbar. The impact transported at least ∼2×1015g of gas from the troposphere to the stratosphere, an amount less than derived for the SL9 C fragment impact. From thermal heating and mass-transport considerations, the diameter of the impactor was roughly in the range of 200-500m, assuming a mean density of 2.5g/cm3. Models with temperature perturbations and ammonia redistribution alone are unable to fit the observed thermal emission; non-gray emission from particulate emission is needed. Mid-infrared spectroscopy of material delivered by the impacting body implies that, in addition to a silicate component, it contains a strong signature that is consistent with silica, distinguishing it from SL9, which contained no evidence for silica. Because no comet has a significant abundance of silica, this result is more consistent with a " rocky" or " asteroidal" origin for the impactor than an " icy" or " cometary" one. This is surprising because the only objects generally considered likely to collide with Jupiter and its satellites are Jupiter-Family Comets, whose populations appear to be orders of magnitude larger than the Jupiter-encountering asteroids. Nonetheless, our conclusion that there is good evidence for at least a major asteroidal component of the impactor composition is also consistent both with constraints on the geometry of the impactor and with results of contemporaneous Hubble Space Telescope observations. If the impact was not simply a statistical fluke, then our conclusion that the impactor contained more rocky material than was the case for the desiccated Comet SL9 implies a larger population of Jupiter-crossing asteroidal bodies than previously estimated, an asteroidal component within the Jupiter-Family Comet population, or compositional differentiation within these bodies. © 2010 Elsevier Inc.

We obtained longitudinally resolved thermal infrared spectra (8-13μm and 17-25μm) of Jupiter's impact debris at the Gemini South Telescope on July 24, 2009; five days after the July 19th collision. These were used to study the mechanisms responsible for the redistribution of thermal energy and material (ammonia and stratospheric particulates) following the impact. Upwelling of (8.5±4.1)×10 14g of tropospheric air was sufficient to deposit (6.7±4.1)×10 12g of NH 3 over a 6° longitude range above the impact core. The NH 3 was distributed over the 20-80mbar region with a peak abundance of 1.0±0.6ppm at 45mbar. Only a 10th of this abundance was observed over the western ejecta, and it is unlikely that these observations were sensitive to NH 3 entrained in the ballistic plume itself. The pattern of excess thermal energy was markedly different from that of Shoemaker-Levy 9 (SL9), with a localized tropospheric perturbation of 2.0±1.0K at 200-300 mbar and a broader stratospheric warming of up to 3.5±2.0K at 10-30mbar. We find no evidence of residual warmth at p

We report Hubble Space Telescope images of Jupiter during the aftermath of an impact by an unknown object in 2009 July. The 2009 impact-created debris field evolved more slowly than those created in 1994 by the collision of the tidally disrupted comet D/Shoemaker-Levy 9 (SL9). The slower evolution, in conjunction with the isolated nature of this single impact, permits a more detailed assessment of the altitudes and meridional motion of the debris than was possible with SL9. The color of the 2009 debris was markedly similar to that seen in 1994, thus this dark debris is likely to be Jovian material that is highly thermally processed. The 2009 impact site differed from the 1994 SL9 sites in UV morphology and contrast lifetime; both are suggestive of the impacting body being asteroidal rather than cometary. Transport of the 2009 Jovian debris as imaged by Hubble shared similarities with transport of volcanic aerosols in Earth's atmosphere after major eruptions.

To coincide with the flyby of the Pluto-bound New Horizons probe, Jupiter was the target of intensive observation, starting in February 2007, from a battery of ground-based telescopes and the Hubble Space Telescope (HST). Weeks into the project, on 25 March, an intense disturbance developed in Jupiter's strongest jet at 23° North latitude, lasting to June 2007. This type of event is rare — the last ones were seen in 1990 and 1975. The onset of the disturbance was captured by the HST, and the development of two plumes was followed in unprecedented detail. The two plumes (bright white spots in the small infrared image on the cover) towered 30 km above the surrounding clouds. The nature of the power source for the jets that dominate the atmospheres of Jupiter and Saturn is a controversial matter, complicated by the interplay of local and planet-wide meteorological factors. The new observations are consistent with a wind extending deep into the atmosphere, well below the level reached by solar radiation. In the larger cover image, turbulence caused by the plumes can be seen in the band that is home to the jet. Observations and modelling of two plumes in Jupiter's atmosphere that erupted at the same latitude as the strongest jet (23° North) are reported. Based on dynamical modelling it is concluded that the data are consistent only with a wind that extends well below the level where solar radiation is deposited. The atmospheres of the gas giant planets (Jupiter and Saturn) contain jets that dominate the circulation at visible levels1,2. The power source for these jets (solar radiation, internal heat, or both) and their vertical structure below the upper cloud are major open questions in the atmospheric circulation and meteorology of giant planets1,2,3. Several observations1 and in situ measurements4 found intense winds at a depth of 24 bar, and have been interpreted as supporting an internal heat source. This issue remains controversial5, in part because of effects from the local meteorology6. Here we report observations and modelling of two plumes in Jupiter’s atmosphere that erupted at the same latitude as the strongest jet (23° N). The plumes reached a height of 30 km above the surrounding clouds, moved faster than any other feature (169 m s-1), and left in their wake a turbulent planetary-scale disturbance containing red aerosols. On the basis of dynamical modelling, we conclude that the data are consistent only with a wind that extends well below the level where solar radiation is deposited.

We present polarization images of Comet ISON (C/2012 S1) taken with the Hubble Space Telescope (HST) on UTC 2013 May 8 (rh = 3.81 AU, Delta = 4.34 AU), when the phase angle was alpha = 12.16 degrees. This phase angle is approximately centered in the negative polarization branch for cometary dust. The region beyond 1000 km from the nucleus shows a negative polarization amplitude of p% -1.6%. Within 1000 km of the nucleus, the polarization position angle rotates to be approximately perpendicular to the scattering plane, with an amplitude p% +2.5%. Such positive polarization has been observed previously as a characteristic feature of cometary jets, and we show that Comet ISON does indeed harbor a jet-like feature. These HST observations of Comet ISON represent the first visible light, imaging polarimetry with sub-arcsecond spatial resolution of a Nearly Isotropic Comet (NIC) beyond 3.8 AU from the Sun at a small phase angle. The observations provide an early glimpse of the properties of the cometary dust preserved in this Oort-cloud comet., Comment: 18 pages, 4 figures. Accepted for publication in Astrophysical Journal Letters

New 5.2-μm thermal images of Saturn's clouds reveal a strong axisymmetric banded structure centered at 45°S with discrete cold spots about 30,000–50,000 km long that: (i) lower the ∼180-K brightness temperature by 8–10 K; (ii) rotate at a rate that is consistent with cloud-tracked zonal winds; and (iii) exhibit no correlation with structures seen in reflected sunlight. They are explained by variations of optical thickness of clouds just below the 1-bar level.

We report the first absolutely calibrated photometry of nine saturnian satellites beyond 1.0 μm, in canonical near-infrared filters, including the first such spectrum of the leading side of Enceladus. The satellites were observed during Ring Plane Crossing in August and September of 1995 with the NSFCAM instrument at the NASA/IRTF. These observations were contemporaneous with those of the uranian system, acquired by K. H. Baines et al. (1998, Icarus132, 266–284), using the same instrument and filters. Results are reported for J, H, and K filters near 1.27, 1.62, and 2.20 μm; a 0.1-μm-wide H′ filter centered at 1.73 μm; and a 0.17-μm-wide K′ filter centered at 2.27 μm. We find that the opposition surge, absolute brightness, and spectral band depths of Enceladus are consistent with fresh water ice, uncontaminated by the kinds of low albedo, spectrally neutral materials encountered in the uranian system. Specifically, Enceladus displays a large near-infrared opposition surge of 0.0817 mag deg−1 between 3.51° and 0.39° solar phase and a peak brightness at 1.27 μm with a geometric albedo of 0.904±0.063, while also having a J–H band depth of about 30%. All of these are consistent with a highly backscattering coating of fresh water frost on the surface of the satellite. The J–H band-depth is consistent with the relatively large (30–56%) water-ice-induced 1.52-μm band depths noted for the other saturnian satellites by Clark et al. (1984, Icarus58, 265–281). By contrast, the darker uranian satellites display a J–H band-depth of less than 10%. From H to 1.73 μm, the full-disk albedo of Enceladus increases by 27%, similar to the uranian satellites. We find that Dione, Janus, and Epimetheus are all brighter on the leading sides than the trailing sides. However, Enceladus is brighter on the trailing side, consistent with 0.89 μm measurements of B. J. Buratti et al. (1998, Icarus136, 223–231) and with the suggestion by M. R. Showalter et al. (1991, Icarus94, 451–473) that negatively charged E-ring particles would preferentially impact Enceladus' trailing side. Further, there is a bluish slope to the satellite's spectrum, similar to that of the E-ring itself. These observations suggest, along with various other lines of evidence, that a substantial and evolving interaction between the E-ring and Enceladus exists, with Enceladus possibly being the source (and sink) of E-ring material. Finally, our results for the 2.27-μm albedos of some of the other saturnian satellites—including Prometheus, Janus, Epimetheus, Mimas, Tethys, Dione, Rhea, and Hyperion, as well as Enceladus—are comparable to the visible albedos reported for these satellites by B. J. Buratti and J. Veverka (1984, Icarus58, 254–264) and D. Morrison et al. (1986, Satellites (Burns and Matthews, Eds.), pp. 764–801).

Scattering Calculations of none-spherical particles have been carried out in order to explain observed optical properties of cometary dust. We focused on two optical properties of cometary dust sensitive to particle shape.

The results of the nephelometer experiment conducted aboard the probe of the Galileo mission to Jupiter are presented. The tenuous clouds and sparse particulate matter in the relatively particle-free 5-μm “hot spot” region of the probe's descent were documented from about 0.46 bar to about 12 bars. Three regions of apparent coherent structure were noted, in addition to many indications of extremely small particle concentrations along the descent path. From the first valid measurement at about 0.46 bar down to about 0.55 bar, a feeble decaying lower portion of a cloud, corresponding with the predicted ammonia particle cloud, was encountered. A denser, but still very modest, particle structure was present in the pressure regime extending from about 0.76 bar to a distinctive base at 1.34 bars and is compatible with the expected ammonium hydrosulfide cloud. No massive water cloud was encountered, although below the second structure, a small, vertically thin layer at about 1.65 bars may be detached from the cloud above, but may also be water condensation, compatible with reported measurements of water abundance from other Galileo Mission experiments. A third small signal region, extending from about 1.9 to 4.5 bars, exhibited quite weak but still distinctive structure and, although the identification of the light scatterers in this region is uncertain, may also be a water cloud, perhaps associated with lateral atmospheric motion and/or reduced to a small mass density by atmospheric subsidence or other causes. Rough descriptions of the particle size distributions and cloud properties in these regions have been derived, although they may be imprecise because of the small signals and experimental difficulties. These descriptions document the small number densities of particles, the moderate particle sizes, generally in the slightly submicron to few micron range, and the resulting small optical depths, mass densities due to particles, column particle number loading, and column mass loading in the atmosphere encountered by the Galileo probe during its descent.

We report the first multi-filter set of absolutely-calibrated near-infrared images of Uranus, its rings, and three major satellites - Titania, Ariel, and Miranda.

Clouds formed on Jupiter by the impact of July 19, 2009 were observed from the IRTF with the same instrument and near-infrared filters during four observing runs over 50 days, beginning one day after impact, providing comprehensive diagnostics of cloudtop altitude, particle size and opacity and yielding quantitative information on the temporal evolution of the impact cloud (IC). The IC evolved relatively rapidly during the first 26 days after impact (Period I) and relatively slowly for the next 23 days (Period II). For the column volume density of the IC core, analyzed over a range of models with varying Mie-scattering particle radii over 0.1–1.1 μm and imaginary indices of refraction ( n i ) from 0.001 to the limiting model-constrained value of 0.03, the Period I e-folding timescale is 4–16 times less than for Period II, with a best-fit timescale of of 23 days (Period I) increasing to 117 days (Period II) for the nominal best-fit case of large (0.7–1.1 μm) dark ( n i =0.01) particles consistent with previous determinations of the size and near-infrared brightness of impact cloud particles ( de Pater et al. Icarus 210, 722–741, 2010 ). Over the entire period, the nominal model mean particle radius ranges from ∼0.85 μm one day after impact to 0.89–1.06 μm 49 days later, considerably larger than the 0.21–0.28 μm particles determined for the Shoemaker Levy 9 impact (SL9; West et al., Science 267, 1296–1301, 1995). The 1.69 and 2.12 μm nominal model IC core opacities show timescales averaged over the entire seven-week period of ∼33 and ∼35 days, respectively, ∼60% longer than the 18–23 day timescales of small-particle models (∼0.36 μm radius) which are more consistent with the ∼15-day visible timescale reported by Sanchez-Lavega et al. (2011, Icarus 214,462–476) . Including the area of the entire IC, we find that the total particle volume over the 49 days changes from ∼0.036 to ∼0.022 km 3 for the nominal model, corresponding to a variation of the diameter of an equivalent sphere from ∼0.41 to ∼0.35 km, close to the ∼10% diameter change over one month reported for SL9 clouds ( West et al, ibid ). Nominal Period II timescales for opacities and total cloud volume – 50–300 days – are 2–11 times longer than nominal Period I timescales; indeed, values of infinity are consistent with the uncertainties. The relatively long timescales found for total cloud dissipation are consistent with (1) material dispersal by wind shears, and (2) relatively weak sedimentation/coagulation, consistent with SL9 results (West et al., ibid). Finally, the IC thickness of ∼1 scale-height permits a vertical windshear of ∼1 m/s, inconsistent with the derived ∼7 m/s cloud spreading, thus implying that the meridional shear is the dominant cloud shear component, as reported for visible measurements (Sanchez-Lavega et al. ibid).

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Mid-infrared 7-20 $\mu$m imaging of Jupiter demonstrates that the increased albedo of Jupiter's South Equatorial Belt (SEB) during the `fade' (whitening) event of 2009-2010 was correlated with changes to atmospheric temperature and aerosol opacity. The opacity of the tropospheric condensation cloud deck at pressures less than 800 mbar increased by 80% between May 2008 and July 2010, making the SEB ($7-17^\circ$ S) as opaque in the thermal infrared as the adjacent equatorial zone. After the cessation of discrete convective activity within the SEB in May 2009, a cool quiescent band of high aerosol opacity (the SEB zone at $11-15^\circ$ S) was observed separating the cloud-free northern and southern SEB components. The cooling of the SEBZ (with peak-to-peak contrasts of $1.0\pm0.5$ K), as well as the increased aerosol opacity at 4.8 and 8.6 $\mu$m, preceded the visible whitening of the belt by several months. A chain of five warm, cloud-free `brown barges' (subsiding airmasses) were observed regularly in the SEB between June 2009 and June 2010, by which time they too had been obscured by the enhanced aerosol opacity of the SEB, although the underlying warm circulation was still present in July 2010. The cool temperatures and enhanced aerosol opacity of the SEBZ after July 2009 are consistent with an upward flux of volatiles from deeper levels (e.g., ammonia-laden air) and enhanced condensation, obscuring the blue-absorbing chromophore and whitening the SEB by April 2010. Revival of the dark SEB coloration in the coming months will ultimately require sublimation of these ices by subsidence and warming of volatile-depleted air. [Abridged], Comment: 22 pages, 11 figures, published in Icarus (2011)

International audience

On 2009 July 19, we observed a single, large impact on Jupiter at a planetocentric latitude of 55^{\circ}S. This and the Shoemaker-Levy 9 (SL9) impacts on Jupiter in 1994 are the only planetary-scale impacts ever observed. The 2009 impact had an entry trajectory opposite and with a lower incidence angle than that of SL9. Comparison of the initial aerosol cloud debris properties, spanning 4,800 km east-west and 2,500 km north-south, with those produced by the SL9 fragments, and dynamical calculations of pre-impact orbit, indicate that the impactor was most probably an icy body with a size of 0.5-1 km. The collision rate of events of this magnitude may be five to ten times more frequent than previously thought. The search for unpredicted impacts, such as the current one, could be best performed in 890-nm and K (2.03-2.36 {\mu}m) filters in strong gaseous absorption, where the high-altitude aerosols are more reflective than Jupiter's primary cloud.

Thermal-IR imaging from space-borne and ground-based observatories was used to investigate the temperature, composition and aerosol structure of Jupiter's Great Red Spot (GRS) and its temporal variability between 1995 and 2008. An elliptical warm core, extending over 8° of longitude and 3° of latitude, was observed within the cold anticyclonic vortex at 21°S. The warm airmass is co-located with the deepest red coloration of the GRS interior. The maximum contrast between the core and the coldest regions of the GRS was 3.0-3.5. K in the north-south direction at 400. mbar atmospheric pressure, although the warmer temperatures are present throughout the 150-500. mbar range. The resulting thermal gradients cause counter-rotating flow in the GRS center to decay with altitude into the lower stratosphere. The elliptical warm airmass was too small to be observed in IRTF imaging prior to 2006, but was present throughout the 2006-2008 period in VLT, Subaru and Gemini imaging.Spatially-resolved maps of mid-IR tropospheric aerosol opacity revealed a well-defined lane of depleted aerosols around the GRS periphery, and a correlation with visibly-dark jovian clouds and bright 4.8-μm emission. Ammonia showed a similar but broader ring of depletion encircling the GRS. This narrow lane of subsidence keeps red aerosols physically separate from white aerosols external to the GRS. The visibility of the 4.8-μm bright periphery varies with the mid-IR aerosol opacity of the upper troposphere. Compositional maps of ammonia, phosphine and para-H2 within the GRS interior all exhibit north-south asymmetries, with evidence for higher concentrations north of the warm central core and the strongest depletions in a symmetric arc near the southern periphery. Small-scale enhancements in temperature, NH3 and aerosol opacity associated with localized convection are observed within the generally-warm and aerosol-free South Equatorial Belt (SEB) northwest of the GRS. The extent of 4.8-μm emission from the SEB varied as a part of the 2007 'global upheaval,' though changes during this period were restricted to pressures greater than 500mbar. Finally, a region of enhanced temperatures extended southwest of the GRS during the survey, restricted to the 100-400mbar range and with no counterpart in visible imaging or compositional mapping. The warm airmass was perturbed by frequent encounters with the cold airmass of Oval BA, but no internal thermal or compositional effects were noted in either vortex during the close encounters. © 2010 Elsevier Inc.

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The similarity of density waves in the rings of Saturn and Uranus are addressed. It is found that all ring systems are grossly similar in that they all encircle the primary in its equatorial plane and exhibit responses to resonant satellite perturbations. The dominant response of Saturn's rings is the clearing of gaps and generation of density and bending waves. The Uranian rings appear to be confined by the presence of shepherd satellites. Three possible density waves have been identified, two in the epsilon ring and one in the delta ring.

Occultation profiles have been derived from Voyager 2 photopolarimeter observations of the nine pre-Voyager Uranian rings as well as of 1986U1R. The epsilon ring, which is the broadest and most massive, is noted to possess a wealth of structure which appears to persist coherently around the ring. The photopolarimeter data do not show any features globally ascribable to all the rings observed. Results are presented from a statistical analysis of photopolarimeter data for previously undetected or partial ring arcs.

A Monte Carlo dust tail model has been applied to extract the dust environment parameters of the comet C/2012 S1 (ISON) from both Earth-based and SOHO LASCO C3 observations, performed from about six astronomical units (AU) inbound, to just after perihelion passage, when only a small portion of the original comet nucleus has survived in the form of a cloud of tiny particles. The early Afρ and image data are consistent with particle ejection from an extended active area located at latitudes 35°N to 90°N (for a prograde rotating nucleus), with the spin axis having a large obliquity (I ∼ 70°). This configuration nicely fits the early images and Afρ data until 3.9 AU inbound, when the emission should become isotropic in order to fit the data. The analysis of LASCO images reveals that, assuming an original nucleus of R{sub N} = 500 m with ρ = 1000 kg m{sup –3}, at least half of its mass was vaporized when the comet was at about 17 R {sub ☉} inbound. We conclude that at that time the nucleus suffered a cataclysmic fragmentation releasing a huge amount of material of 2.3 ×10{sup 11} kg, equivalent to a sphere of 380 m more » in radius with density 1000 kg m{sup –3}. The surviving material after perihelion passage consists of very small dust particles of 0.1-50 μm in radius with a total mass of just 6.7×10{sup 8} kg. « less

Earth-based observations of Jupiter indicate that the Galileo probe probably entered Jupiter's atmosphere just inside a region that has less cloud cover and drier conditions than more than 99 percent of the rest of the planet. The visual appearance of the clouds at the site was generally dark at longer wavelengths. The tropospheric and stratospheric temperature fields have a strong longitudinal wave structure that is expected to manifest itself in the vertical temperature profile.

The spatial organization and time dependence of Jupiter's temperatures near 250-millibar pressure were measured through a jovian year by imaging thermal emission at 18 micrometers. The temperature field is influenced by seasonal radiative forcing, and its banded organization is closely correlated with the visible cloud field. Evidence was found for a quasi-periodic oscillation of temperatures in the Equatorial Zone, a correlation between tropospheric and stratospheric waves in the North Equatorial Belt, and slowly moving thermal features in the North and South Equatorial Belts. There appears to be no common relation between temporal changes of temperature and changes in the visual albedo of the various axisymmetric bands.

The National Aeronautics and Space Administration (NASA) Infrared Telescope Facility was used to investigate the collision of comet Shoemaker-Levy 9 with Jupiter from 12 July to 7 August 1994. Strong thermal infrared emission lasting several minutes was observed after the impacts of fragments C, G, and R. All impacts warmed the stratosphere and some the troposphere up to several degrees. The abundance of stratospheric ammonia increased by more than 50 times. Impact-related particles extended up to a level where the atmospheric pressure measured several millibars. The north polar near-infrared aurora brightened by nearly a factor of 5 a week after the impacts.