Saturn's aurora observed by the Cassini camera at visible wavelengths

The first observations of Saturn's visible-wavelength aurora were made by the Cassini camera. The aurora was observed between 2006 and 2013 in the northern and southern hemispheres. The color of the aurora changes from pink at a few hundred km above the horizon to purple at 1000-1500 km above the horizon. The spectrum observed in 9 filters spanning wavelengths from 250 nm to 1000 nm has a prominent H-alpha line and roughly agrees with laboratory simulated auroras. Auroras in both hemispheres vary dramatically with longitude. Auroras form bright arcs between 70 and 80 degree latitude north and between 65 and 80 degree latitude south, which sometimes spiral around the pole, and sometimes form double arcs. A large 10,000-km-scale longitudinal brightness structure persists for more than 100 hours. This structure rotates approximately together with Saturn. On top of the large steady structure, the auroras brighten suddenly on the timescales of a few minutes. These brightenings repeat with a period of about 1 hour. Smaller, 1000-km-scale structures may move faster or lag behind Saturn's rotation on timescales of tens of minutes. The persistence of nearly-corotating large bright longitudinal structure in the auroral oval seen in two movies spanning 8 and 11 rotations gives an estimate on the period of 10.65 $\pm$0.15 h for 2009 in the northern oval and 10.8$\pm$ 0.1 h for 2012 in the southern oval. The 2009 north aurora period is close to the north branch of Saturn Kilometric Radiation (SKR) detected at that time.Comment: 39 pages, 8 figures, 1 table, 6 supplementary movies, accepted to Icaru

Lightning detection in planetary atmospheres

Lightning in planetary atmospheres is now a well-established concept. Here we discuss the available detection techniques for, and observations of, planetary lightning by spacecraft, planetary landers and, increasingly, sophisticated terrestrial radio telescopes. Future space missions carrying lightning-related instrumentation are also summarised, specifically the European ExoMars mission and Japanese Akatsuki mission to Venus, which could both yield lightning observations in 2016.Comment: Accepted for publication in Weather as part of a special issue on Advances in Lightning Detectio

Cassini Imaging Science: Initial Results on Saturn's Atmosphere

The Cassini Imaging Science Subsystem (ISS) began observing Saturn in early February 2004. From analysis of cloud motions through early October 2004, we report vertical wind shear in Saturn's equatorial jet and a maximum wind speed of ∼375 meters per second, a value that differs from both Hubble Space Telescope and Voyager values. We also report a particularly active narrow southern mid-latitude region in which dark ovals are observed both to merge with each other and to arise from the eruptions of large, bright storms. Bright storm eruptions are correlated with Saturn's electrostatic discharges, which are thought to originate from lightning

Light Scattering in the Clouds on Jupiter

We construct maps of jovian cloud properties from images taken simultaneously by the Galileo solid state imaging system (SSI) and the near-infrared mapping spectrometer (NIMS) at 26 visible and near infrared wavelengths, ranging from 0.41 to 5.2 µm. Three regions - the Great Red Spot (GRS), a 5-micron Hot Spot, and one of the White Ovals - are studied. We perform a principal component analysis (PCA) on the multispectral images. PCA shows that the pixel-to-pixel variations at the different wavelengths are highly correlated, and that 91% of the variance in the data can be summarized using only three maps. The three maps are combined into one color map, which indicates different 26-wavelength spectra as different colors. Using the representative spectra for each color we compare different areas on the map qualitatively. We find that in the GRS there is a red chromophore which is associated with clouds that block 5-µm emission. At the hot spot and white oval regions there is no chromophore associated with clouds. Most of the bright, optically thick clouds blocking thermal emission are also extended vertically to the upper troposphere. Some of the bright, optically thick clouds blocking thermal emission are deep and do not extend vertically to the upper troposphere. A small convective stormlike cloud to the northwest of the GRS is unusually reflective at long wavelengths (4µm) and might indicate large particles. We study lightning on Jupiter and the clouds illuminated by the lightning. The Galileo SSI lightning images have a resolution of 25 km/pixel and are able to resolve the diffuse spots of light scattered in the clouds, which have full widths at half maximum in the range 90-160 km. We compare the lightning images with the images produced by our 3D Monte Carlo light scattering model. The model reproduces non isotropic non-conservative scattering of the photons in the non-homogeneous opacity distribution. We derive that some of the observed scattering patterns are produced in a 3D cloud rather than in a plane-parallel cloud layer, suggesting deep convection. For the six flashes studied, the clouds above the lightning are optically thick (Γ > 5). Lightning is as deep as the bottom of the water cloud. Jovian flashes are more regular and circular than the largest terrestrial flashes observed from space.</p

Income taxation as a tool of income redistribution

© 2015, Mediterranean Center of Social and Educational Research. All rights reserved. Many countries use income taxation as one of the essential tools of income redistribution. This paper covers positive and negative effect of the proportional scale of individual taxation introduced by the Russian Federation. The observation suggests that the flat rate increases the social inequality, which, in turn, reflects adversely on the economic growth of the country. The document describes the contribution of the income tax to the budget revenues of the developed countries and provides the data of foreign practice to apply income tax rates. The authors demonstrate the need for the progressive taxation and establishment of a tax-free allowance

Cassini ISS Observation of Saturn’s North Polar Vortex and Comparison to the South Polar Vortex

We present analyses of Saturn’s north pole using high-resolution images captured in late 2012 by the Cassini spacecraft’s Imaging Science Subsystem (ISS) camera. The images reveal the presence of an intense cyclonic vortex centered at the north pole. In the red and green visible continuum wavelengths, the north polar region exhibits a cyclonically spiraling cloud morphology extending from the pole to 85°N planetocentric latitude, with a 4700 km radius. Images captured in the methane bands, which sense upper tropospheric haze, show an approximately circular hole in the haze extending up to 1.5° latitude away from the pole. The spiraling morphology and the “eye”-like hole at the center are reminiscent of a terrestrial tropical cyclone. In the System III reference frame (rotation period of 10h39m22.4s, Seidelmann et al. 2007; Archinal et al. 2011), the eastward wind speed increases to about 140 m s^(−1) at 89°N planetocentric latitude. The vorticity is (6.5± 1.5)×10^(−4)s^(−1) at the pole, and decreases to (1.3± 1.2)×10^(−4)s^(−1) at 89°N. In addition, we present an analysis of Saturn’s south polar vortex using images captured in January 2007 to compare its cloud morphology to the north pole. The set of images captured in 2007 includes filters that have not been analyzed before. Images captured in the violet filter (400 nm) also reveal a bright polar cloud. The south polar morphology in 2007 was more smooth and lacked the small clouds apparent around the north pole in 2012. Saturn underwent equinox in August 2009. The 2007 observation captured the pre-equinox south pole, and the 2012 observation captured the post-equinox north pole. Thus, the observed differences between the poles are likely due to seasonal effects. If these differences indeed are caused by seasonal effects, continuing observations of the summer north pole by the Cassini mission should show a formation of a polar cloud that appears bright in short-wavelength filters

Phase light curves for extrasolar Jupiters and Saturns

We predict how a remote observer would see the brightness variations of giant planets similar to Jupiter and Saturn as they orbit their central stars. We model the geometry of Jupiter, Saturn and Saturn's rings for varying orbital and viewing parameters. Scattering properties for the planets and rings at wavelenghts 0.6-0.7 microns follow Pioneer and Voyager observations, namely, planets are forward scattering and rings are backward scattering. Images of the planet with or without rings are simulated and used to calculate the disk-averaged luminosity varying along the orbit, that is, a light curve is generated. We find that the different scattering properties of Jupiter and Saturn (without rings) make a substantial difference in the shape of their light curves. Saturn-size rings increase the apparent luminosity of the planet by a factor of 2-3 for a wide range of geometries. Rings produce asymmetric light curves that are distinct from the light curve of the planet without rings. If radial velocity data are available for the planet, the effect of the ring on the light curve can be distinguished from effects due to orbital eccentricity. Non-ringed planets on eccentric orbits produce light curves with maxima shifted relative to the position of the maximum planet's phase. Given radial velocity data, the amount of the shift restricts the planet's unknown orbital inclination and therefore its mass. Combination of radial velocity data and a light curve for a non-ringed planet on an eccentric orbit can also be used to constrain the surface scattering properties of the planet. To summarize our results for the detectability of exoplanets in reflected light, we present a chart of light curve amplitudes of non-ringed planets for different eccentricities, inclinations, and the viewing azimuthal angles of the observer.Comment: 40 pages, 13 figures, submitted to Ap.

Photometric Orbits of Extrasolar Planets

We define and analyze the photometric orbit (PhO) of an extrasolar planet observed in reflected light. In our definition, the PhO is a Keplerian entity with six parameters: semimajor axis, eccentricity, mean anomaly at some particular time, argument of periastron, inclination angle, and effective radius, which is the square root of the geometric albedo times the planetary radius. Preliminarily, we assume a Lambertian phase function. We study in detail the case of short-period giant planets (SPGPs) and observational parameters relevant to the Kepler mission: 20 ppm photometry with normal errors, 6.5 hour cadence, and three-year duration. We define a relevant "planetary population of interest" in terms of probability distributions of the PhO parameters. We perform Monte Carlo experiments to estimate the ability to detect planets and to recover PhO parameters from light curves. We calibrate the completeness of a periodogram search technique, and find structure caused by degeneracy. We recover full orbital solutions from synthetic Kepler data sets and estimate the median errors in recovered PhO parameters. We treat in depth a case of a Jupiter body-double. For the stated assumptions, we find that Kepler should obtain orbital solutions for many of the 100-760 SPGP that Jenkins & Doyle (2003) estimate Kepler will discover. Because most or all of these discoveries will be followed up by ground-based radial-velocity observations, the estimates of inclination angle from the PhO may enable the calculation of true companion masses: Kepler photometry may break the "m sin i" degeneracy.Comment: V1: 27 pages, 12 figures, 2 tables - submitted to ApJ; V2: 31 pages, 16 figures, 2 tables - accepted by Ap

Photometric Phase Variations of Long-Period Eccentric Planets

The field of exoplanetary science has diversified rapidly over recent years as the field has progressed from exoplanet detection to exoplanet characterization. For those planets known to transit, the primary transit and secondary eclipse observations have a high yield of information regarding planetary structure and atmospheres. The current restriction of these information sources to short-period planets may be abated in part through refinement of orbital parameters. This allows precision targeting of transit windows and phase variations which constrain the dynamics of the orbit and the geometric albedo of the atmosphere. Here we describe the expected phase function variations at optical wavelengths for long-period planets, particularly those in the high-eccentricity regime and multiple systems in resonant and non-coplanar orbits. We apply this to the known exoplanets and discuss detection prospects and how observations of these signatures may be optimized by refining the orbital parameters.Comment: 9 pages, 8 figures, accepted for publication in Ap