Search

Abstract: Titan's atmosphere has been extensively studied during the Cassini–Huygens Mission. The polar environment undergoes considerable seasonal variation and is distinct from the more quiescent equatorial environment experienced by the Huygens probe in 2005. The thermal structure of the upper atmosphere is affected by interaction of Titan's atmosphere with the plasma and energetic particles in Saturn's magnetosphere or in the solar wind. Titan's polar regions, and its hydrocarbon lakes in particular, are of interest for future exploration as is the complex organic chemistry that takes place in the upper atmosphere. Thus, specific environmental models are required for future exploration. Furthermore, the models developed to support the design of Huygens had to accommodate wide uncertainties, requiring large design margins. The extensive observations by the Cassini spacecraft (and indeed Huygens itself) provide a basis for narrowing these uncertainties, notably in composition. We provide a description of these new data sets, their scientific basis, and present limitations. The empirically constrained neutral temperatures and densities presented here also have important implications for fundamental chemical modeling. The empirical modeling presented here provides constraints on these models, which will lead to improved estimations of chemical products. Therefore, the paper describes a new model of Titan's atmospheric structure to guide both scientific studies and future engineering studies of exploration of the Saturn system. Of particular interest are aero-capture and aero-braking missions that may enable future exploration of the Saturnian satellite system. [Copyright &y& Elsevier]

Abstract: The Cassini spacecraft Radio and Plasma Wave Science (RPWS) Langmuir Probe (LP) provides in-situ measurements of Titan's ionosphere. We present here data from 47 deep flybys in the time period October 2004–July 2012 of charge densities of positive and negative ions as well as electrons. These densities have been mapped with respect to altitude and solar zenith angle (SZA) in an altitude range of 880–1400km. The inferred electron number densities are consistent with earlier presented observational results. Negative ion charge densities exhibit a trend that exponentially increases towards lower altitudes within the covered altitude range. This is especially evident on the nightside of Titan (SZA >110°). The negative ion charge densities at the lowest traversed altitudes (near 960km) are inferred to be in the range 300–2500cm−3. The results show that very few free electrons (n e /n i ∼0.1–0.7) exist in the deepest regions (880–1050km) of Titan's nightside ionosphere. Instead the deep nightside part of Titan's ionosphere is dominated by both negatively and positively charged heavy (>100amu) organic ions. We therefore believe a dust/aerosol-ion plasma exists here, similar to what is found in noctilucent clouds in Earth's mesosphere. [Copyright &y& Elsevier]

Basic documents that are made according to measurements and topographic surveying for the purpose of creating various projects are plans and topographic maps. Achieving these documents must accurately represent the earth's surface with its representative elements. These documents are made by using cartographic projections that must be analyzed according to the quality of the representation in order to obtain plans and maps with high accuracy and superior quality. Regarding the elements that can be deformed within a projection, these are angles, distance or acres. Between the years 1855-1857, the first map of Wallachia was made (also known as "Satmari Map") using the scale 1:57 600. This map contains the historical provinces Wallachia and Oltenia, and it is the first map under the name of Romania. After the First World War, due to economic, political and administrative reasons, the necessity arose for a large-scale map (1:20 000, 1:10 000 or even 1:5 000) by reproducing and multiplying existing land originals. The new cartographic documents, known as "drawing master plans" were drawn up in a unique projection throughout the country, namely the Lambert projection. After the Second World War, the Romanian Cartography has strongly developed. Thus, in order to obtain plans and topographic maps in the shortest time and at the lowest possible price, the Photogrammetry Center was established in 1958, which later in 1970 became the Institute of Geodesy, Photogrammetry, Cartography and Land Management (IGFCOT), where plans were drawn up to the scales 1:2 000, 1:5 000 and 1:10 000 required either by national economy, or for land records, or to urban planning. The modern topographic map was also created to the scale 1:25 000 (1972-1981) using the Gauss-Krüger transverse cylindrical projection. In Romania, over time many cartographic projections were used to create basic maps, as follows: Muffling polyhedral projection introduced in 1873 - for the Austrian map covering also Transilvania; Cassini cylindrical projection introduced in 1876 based on Bessel ellipsoid; Bonne equivalent conical projection introduced in 1873, based on Clarke 1880 and Bessel 1841 ellipsoid; Lambert- Cholesky conformal conic projection - introduced in 1917, based on Clarke ellipsoid; Gauss Kruger transverse cylindrical conformal projection introduced in 1951, based on ellipsoid Krasovski 1940; Stereographic secant conformal perspective azimuthal projection 1970 plan introduced in 1970, based on ellipsoid Krasovski 1940;UTM conformal secant transversal cylindrical projection (Universal Transverse Mercator) introduced in 1947 based on WGS 84 ellipsoid. [ABSTRACT FROM AUTHOR]

Abstract: Even though the solar wind is highly supersonic, intense ultra-low frequency (ULF) wave activity has been detected in regions just upstream of the bow shocks of magnetized planets. This feature was first observed ahead of the Earth's bow shock, and the corresponding region was called the ULF wave foreshock, which is embedded within the planet's foreshock. The properties as well as the spatial distribution of ULF waves within the Earth's foreshock have been extensively studied over the last three decades and have been explained as a result of plasma instabilities triggered by solar wind ions backstreaming from the bow shock. Since July 2004, the Cassini spacecraft has characterized the Saturnian plasma environment including its upstream region. Since Cassini's Saturn orbit insertion (SOI) in June 2004 through August 2005, we conducted a detailed survey and analysis of observations made by the Vector Helium Magnetometer (VHM). The purpose of the present study is to characterize the properties of waves observed in Saturn's ULF wave foreshock and identify its boundary using single spacecraft techniques. The amplitude of these waves is usually comparable to the mean magnetic field intensity, while their frequencies in the spacecraft frame yields two clearly different types of waves: one with frequencies below the local proton cyclotron frequency ( ) and another with frequencies above . All the wave crossings described here, clearly show that these waves are associated to Saturn's foreshock. In particular, the presence of waves is associated with the change in to quasi-parallel geometries. Our results show the existence of a clear boundary for Saturn's ULF wave foreshock, compatible with surfaces. [Copyright &y& Elsevier]

Abstract: The Cassini Imaging Science Subsystem (ISS) acquired many high-resolution images (<1km/pixel) of the Icy Saturnian satellites during the nominal mission of the Cassini spacecraft between 2004 and 2008. These images were used to create high-resolution mosaics of these satellites. The Cassini mission is expected to continue till 2017 and high-resolution images of the first three years of the extension were used to improve the mosaics, especially in the Northern parts which were not illuminated during the nominal mission. These improved mosaics were the baseline for new versions of the atlases of Mimas, Enceladus, and Dione described in this paper. These new atlases supersede the previous versions from 2006 (Enceladus) and 2008 (Mimas and Dione), and include the official names of additional features, proposed by the Cassini imaging team, approved by the International Astronomical Union (IAU). The new atlases are available to the public through the Imaging Team''s website and the Planetary Data System (PDS). [Copyright &y& Elsevier]

Abstract: We present plasma data from the Cassini Radio and Plasma Wave Science (RPWS) Langmuir probe (LP), mapping the ion density and velocity of Saturn''s inner plasma torus. Data from 129 orbits, recorded during the period from the 1st of February 2005 to the 27th of June 2010, are used to map the extension of the inner plasma torus. The dominant part of the plasma torus is shown to be located in between 2.5 and 8 Saturn radii (1RS=60,268km) from the planet, with a north-southward extension of . The plasma disk ion density shows a broad maximum in between the orbits of Enceladus and Tethys. Ion density values vary between 20 and 125cm−3 at the location of the density maximum, indicating considerable dynamics of the plasma disk. The equatorial density structure, , shows a slower decrease away from the planet than towards. The outward decrease, from 5RS, is well described by the relation . The plume of the moon Enceladus is clearly visible as an ion density maximum of 105 cm−3, only present at the south side of the ring plane. A less prominent density peak, of 115cm−3, is also detected at the orbit of Tethys, at . No density peaks are recorded at the orbits of the moons Mimas, Dione, and Rhea. The presented ion velocity shows a clear general trend in the region between 3 and 7RS, described by . The average starts to deviate from corotation at around 3RS, reaching of corotation close to 5RS. [Copyright &y& Elsevier]

Abstract: We have processed all images of Titan''s surface acquired by the Visual and Infrared Mapping Spectrometer between 2004 and 2010, with the objective of producing seamless global mosaics of the surface in the six infrared atmospheric windows at 1.08, 1.27, 1.59, 2.03, 2.6–2.7 and 5μm. A systematic study of the photometry at 5μm, where haze scattering can be neglected, shows that the surface behaves to first order like a Lambert surface. The results at 5μm are generalized to lower wavelengths, adding an empirical correction accounting for scattering from atmospheric aerosols, using methane band wings as a proxy for the calculation of the scattering additive term. Mosaics incorporating this empirical correction for the geometry and haze scattering show significantly less seams than any previous maps integrating data acquired over such a wide range of observing geometries, and may therefore be used for the study of surface properties. We provide several suggestions for further studies aimed at improving the global mapping of the surface of Titan. With the considered thresholds limits on the acquisition parameters, we found that 13% of Titan''s surface has been mapped at an instrument resolution better than 10km/pixel, 56% of the surface was seen at a resolution between 10 and 20km/pixel, and 24% of the coverage falls in the range 20–50km/pixel. [Copyright &y& Elsevier]

Abstract: Potential encore-mission scenarios have been considered for the Cassini mission. In this paper we discuss one of the end-of-life scenarios in which the Cassini spacecraft could perform a Saturn escape via gravity assists from Titan. It is shown that such satellite-aided escape requires a small deterministic maneuver (e.g., Δv<50m/s), but provides enough energy for the Cassini spacecraft to reach a range of targets in our Solar System, as close to the Sun as the asteroid belt or as far as the Kuiper belt. The escape sequence could be initiated from an arbitrary point during the on-going Cassini mission. Example tours are presented in which the final Titan flyby places the spacecraft into ballistic trajectories that reach Jupiter, Uranus, and Neptune. After years of heliocentric flight, the spacecraft could impact on the target gas giant or perform a flyby to escape from the Solar System (if not to another destination). The concept can be generalized to a new kind of missions, including nested-grand tours, which may involve satellite-aided captures and escapes at more than one planet. [Copyright &y& Elsevier]

Abstract: Cassini radar images of Titan''s surface reveal numerous dark circular features in the equatorial region. These may be related to methane sublimation and have been interpreted as pits. In the T8 equatorial swath, we identify 199 individual pits and estimate their diameters. We analyze the observed spatial distribution and size to characterize these features and understand their formation. Chi-square analysis confirms a significant deviation from a random distribution and shows clustering over the entire swath. However, analysis of the densest cluster of pits, a group of 50, shows a more random distribution. Fractal analysis and comparison with a same-sized random set find only a hint of linearity. A Poisson distribution fits the observed pit-sizes, although resolution limits size determination for the smallest pits, those less than 1km in diameter. Models for random pit generation and evolution simulate the observed Poisson distribution of pit sizes, with larger pits forming by the coalescing of smaller, overlapping ones. Pits, estimated to cover 0.5% of the equatorial T8 swath, could be an erosion mechanism that significantly contributes to the negative skew that has been observed in Titan''s hypsography. [Copyright &y& Elsevier]

Abstract: The Cassini Imaging Science Subsystem (ISS) acquired 370 high-resolution images (<500m/pixel) of Rhea during two close flybys and 9 non-targeted flybys between 2004 and 2010. We combined these images with lower-resolution Cassini images and others taken by the Voyager cameras to produce a high-resolution semi-controlled mosaic of Rhea. This global mosaic is the baseline for a high-resolution Rhea atlas. The nomenclature used in this atlas was proposed by the Cassini imaging team and approved by the International Astronomical Union (IAU). The atlas is available to the public through the Imaging Team''s website 〈http://ciclops.org/maps〉 and the Planetary Data System 〈http://pds.jpl.nasa.gov〉. This atlas completes the series of the atlases of the Saturnian medium-sized satellites Mimas, Enceladus, Tethys, Dione, Rhea, and Iapetus. [Copyright &y& Elsevier]

Both the Gershgorin and Brauer eigenvalue inclusion sets reduce to a single disc when applied to a matrix with a constant main diagonal. We show that a union of ovals of Cassini containing all the eigenvalues of such a matrix can nonetheless be derived and that this union is guaranteed to lie inside the Brauer set. We then apply our results to Toeplitz matrices. [ABSTRACT FROM PUBLISHER]

Abstract: Saturn''s Moon Titan has a thick atmosphere with a meteorological cycle. We report on the evolution of the giant cloud system covering its north pole using observations acquired by the Visual and Infrared Mapping Spectrometer onboard the Cassini spacecraft. A radiative transfer model in spherical geometry shows that the clouds are found at an altitude between 30 and 65km. We also show that the polar cloud system vanished progressively as Titan approached equinox in August 2009, revealing at optical wavelengths the underlying sea known as Kraken Mare. This decrease of activity suggests that the north-polar downwelling has begun to shut off. Such a scenario is compared with the Titan global circulation model of , which predicts a decrease of cloud coverage in northern latitudes at the same period of time. [Copyright &y& Elsevier]

Abstract: Titan''s fluvial channels have been investigated based on data obtained by the Synthetic Aperture Radar (SAR) instrument and the Visible and Infrared Mapping Spectrometer (VIMS) onboard the Cassini spacecraft. In this paper, a database of fluvial features is created based on radar-SAR data aiming to unveil the distribution and the morphologic and spectral characteristics of valleys on Titan on a global scale. It will also study the spatial relations between fluvial valleys and Titan''s geologic units and spectral surface units which have become accessible thanks to Cassini-VIMS data. Several distinct morphologic types of fluvial valleys can be discerned by SAR-images. Dendritic valley networks appear to have much in common with terrestrial dendritic systems owing to a hierarchical and tree-shaped arrangement of the tributaries which is indicative of an origin from precipitation. Dry valleys constitute another class of valleys resembling terrestrial wadis, an indication of episodic and strong flow events. Other valley types, such as putative canyons, cannot be correlated with rainfall based on their morphology alone, since it cannot be ruled out that they may have originated from volcanic/tectonic action or groundwater sapping. Highly developed and complex fluvial networks with channel lengths of up to 1200km and widths of up to 10km are concentrated only at a few locations whereas single valleys are scattered over all latitudes. Fluvial valleys are frequently found in mountainous areas. Some terrains, such as equatorial dune fields and undifferentiated plains at mid-latitudes, are almost entirely free of valleys. Spectrally, fluvial terrains are often characterized by a high reflectance in each of Titan''s atmospheric windows, as most of them are located on Titan''s bright ‘continents’. Nevertheless, valleys are spatially associated with a surface unit appearing blue due to its higher reflection at in a VIMS false color RGB composite with R: , G: , and B: ; the channels either dissect pure bluish surface units or they are carved into terrain with a mixed spectral signature between bright and bluish surface materials. The global picture of fluvial flows clearly indicates a high diversity of parameters controlling fluvial erosion, such as climatic processes, as well as surface and bedrock types. Recent fluvial activity is very likely in the north polar region in contrast to more arid conditions at lower latitudes and at the south pole of Titan. This divergence is probably an indication of seasonal climatic asymmetries between the hemispheres. However, traces of previous fluvial activity are scattered over all latitudes of Titan, which is indicative of previous climatic conditions with at least episodic rainfall. [Copyright &y& Elsevier]

His improved telescope gave Huygens a better vision of the sky, but his ideas about light lay buried for a century. [ABSTRACT FROM AUTHOR]

Saturn's rich magnetospheric environment is unique in the solar system, with a large number of active magnetospheric processes and phenomena. Observations of this environment from the Cassini spacecraft has enabled the study of a magnetospheric system which strongly interacts with other components of the saturnian system: the planet, its rings, numerous satellites (icy moons and Titan) and various dust, neutral and plasma populations. Understanding these regions, their dynamics and equilibria, and how they interact with the rest of the system via the exchange of mass, momentum and energy is important in understanding the system as a whole. Such an understanding represents a challenge to theorists, modellers and observers. Studies of Saturn's magnetosphere based on Cassini data have revealed a system which is highly variable which has made understanding the physics of Saturn's magnetosphere all the more difficult. Cassini's combination of a comprehensive suite of magnetospheric fields and particles instruments with excellent orbital coverage of the saturnian system offers a unique opportunity for an in-depth study of the saturnian plasma and fields environment. In this paper knowledge of Saturn's equatorial magnetosphere will be presented and synthesised into a global picture. Data from the Cassini magnetometer, low-energy plasma spectrometers, energetic particle detectors, radio and plasma wave instrumentation, cosmic dust detectors, and the results of theory and modelling are combined to provide a multi-instrumental identification and characterisation of equatorial magnetospheric regions at Saturn. This work emphasises the physical processes at work in each region and at their boundaries. The result of this study is a map of Saturn's near equatorial magnetosphere, which represents a synthesis of our current understanding at the end of the Cassini Prime Mission of the global configuration of the equatorial magnetosphere. [ABSTRACT FROM AUTHOR]

The interplanetary space probe Cassini/Huygens reached Saturn in July 2004 after 7 years of cruise phase. The German cosmic dust analyser (CDA) was developed under the leadership of the Max Planck Institute for Nuclear Physics in Heidelberg under the support of the DLR e.V. This instrument measures the interplanetary, interstellar and planetary dust in our solar system since 1999 and provided unique discoveries. In 1999, CDA detected interstellar dust in the inner solar system followed by the detection of electrical charges of interplanetary dust grains during the cruise phase between Earth and Jupiter. The instrument determined the composition of interplanetary dust and the nanometre-sized dust streams originating from Jupiter's moon Io. During the approach to Saturn in 2004, similar streams of submicron grains with speeds in the order of 100 km/s were detected from Saturn's inner and outer ring system and are released to the interplanetary magnetic field. Since 2004 CDA measured more than one million dust impacts characterising the dust environment of Saturn. The instrument is one of the three experiments which discovered the active ice geysers located at the south pole of Saturn's moon Enceladus in 2005. Later, a detailed compositional analysis of the water ice grains in Saturn's E ring system led to the discovery of large reservoirs of liquid water (oceans) below the icy crust of Enceladus. Finally, the determination of the dust-magnetosphere interaction and the discovery of the extended E ring (at least twice as large as predicted) allowed the definition of a dynamical dust model of Saturn's E ring describing the observed properties. This paper summarizes the discoveries of a 10-year story of success based on reliable measurements with the most advanced dust detector flown in space until today. This paper focuses on cruise results and findings achieved at Saturn with a focus on flux and density measurements. CDA discoveries related to the detailed dust stream dynamics, E ring dynamics, its vertical profile and E ring compositional analysis are published elsewhere (see Hus et al. in AIP Conference Proccedings 1216:510-513, ; Hsu et al. in Icarus 206:653-661, ; Kempf et al. in Icarus 193:420, ; 206(2):446, ; Postberg et al. in Icarus 193(2):438, ; Nature 459:1098, ; Nature, , doi:). [ABSTRACT FROM AUTHOR]

Abstract: The helium resonance line at 584Å has been observed with the UltraViolet Imaging Spectrograph (UVIS) Extreme Ultraviolet channel during the flyby of Venus by Cassini at a period of high solar activity. The brightness was measured along the disk from the morning terminator up to the bright limb near local noon. The mean disk intensity was ∼320R, reaching ∼700R at the bright limb. These values are slightly higher than those determined from previous observations. The sensitivity of the 584Å intensity to the helium abundance is analyzed using recent cross-sections and solar irradiance measurements at 584Å. The intensity distribution along the UVIS footprint on the disk is best reproduced using the EUVAC solar flux model and the helium density distribution from the VTS3 empirical model. It corresponds to a helium density of 8×106 cm−3 at the level of where the CO2 is 2×1010 cm−3. [Copyright &y& Elsevier]

Abstract: During the final three of the five consecutive and similar Cassini Titan flybys T55–T59 we observe a region characterized by high plasma densities (electron densities of 1–8cm−3) in the tail/nightside of Titan. This region is observed progressively farther downtail from pass to pass and is interpreted as a plume of ionospheric plasma escaping Titan, which appears steady in both location and time. The ions in this plasma plume are moving in the direction away from Titan and are a mixture of both light and heavy ions with composition revealing that their origin are in Titan''s ionosphere, while the electrons are more isotropically distributed. Magnetic field measurements indicate the presence of a current sheet at the inner edge of this region. We discuss the mechanisms behind this outflow, and suggest that it could be caused by ambipolar diffusion, magnetic moment pumping or dispersive Alfvén waves. [Copyright &y& Elsevier]

Abstract: We present RPWS Langmuir probe data from the third Enceladus flyby (E3) showing the presence of dusty plasma near Enceladus’ South Pole. There is a sharp rise in both the electron and ion number densities when the spacecraft traverses through Enceladus plume. The ion density near Enceladus is found to increase abruptly from about 102 cm−3 before the closest approach to 105 cm−3 just 30s after the closest approach, an amount two orders of magnitude higher than the electron density. Assuming that the inconsistency between the electron and ion number densities is due to the presence of dust particles that are collecting the missing electron charges, we present dusty plasma characteristics down to sub-micron particle sizes. By assuming a differential dust number density for a range in dust sizes and by making use of Langmuir probe data, the dust densities for certain lower limits in dust size distribution were estimated. In order to achieve the dust densities of micrometer and larger sized grains comparable to the ones reported in the literature, we show that the power law size distribution must hold down to at least 0.03μm such that the total differential number density is dominated by the smallest sub-micron sized grains. The total dust number density in Enceladus’ plume is of the order of 102 cm−3 reducing to 1cm−3 in the E-ring. The dust density for micrometer and larger sized grains is estimated to be about 10−4 cm−3 in the plume while it is about 10−6–10−7 cm−3 in the E-ring. Dust charge for micron sized grains is estimated to be about eight thousand electron charges reducing to below one hundred electron charges for 0.03μm sized grains. The effective dusty plasma Debye length is estimated and compared with inter-grain distance as well as the electron Debye length. The maximum dust charging time of 1.4h is found for 0.03μm sized grains just 1min before the closest approach. The charging time decreases substantially in the plume where it is only a fraction of a second for 1μm sized grains, 1s for 0.1μm sized grains and about 10s for 0.03μm sized grains. [Copyright &y& Elsevier]

Abstract: The MIMI experiment (Magnetosphere Imaging Instrument) onboard Cassini is dedicated to the study of energetic particles, with in particular LEMMS analyzing charged particles, or the INCA detector which can image the Energetic Neutral Atoms produced by charge exchange collisions between cold neutrals and energetic ions. The MIMI experiment is thus well adapted to the study of the interaction between the Titan nitrogen rich atmosphere and the energetic Saturnian magnetospheric plasma. We analyze here the energetic protons at the Titan orbit crossings before January 2008 (MIMI-LEMMS data; 27–255keV), which are very dynamic, with tri-modal flux spectra and probably quasi-isotropic pitch angle distributions. We provide statistical parameters for the proton fluxes, leading to estimates of the average energy deposition into Titan''s atmosphere, before we discuss the possible influence of Titan on the magnetopause. We then analyze the H ENA images (24–55keV) during the Titan flybys before June 2006 to obtain a better diagnostic of the Titan interaction: the ENAs variability is mostly related to the magnetospheric variability (the exosphere being roughly stable) or the distance from the moon, the ENAs halo around Titan is very stable (corresponding to a lower limit for ENAs emission at the exobase), and strong asymmetries are observed, due to finite gyroradii effects for the parent ions. [Copyright &y& Elsevier]

Abstract: We present a hybrid simulation study (kinetic ions, fluid electrons) of Titan''s plasma interaction during an excursion of this moon from Saturn''s magnetosphere into its magnetosheath, as observed for the first time during Cassini''s T32 flyby on 13 June 2007. In contrast to earlier simulations of Titan''s plasma environment under non-stationary upstream conditions, our model considers a difference in the flow directions of magnetospheric and magnetosheath plasma. Two complementary scenarios are investigated, with the flow directions of the impinging magnetospheric/magnetosheath plasmas being (A) antiparallel and (B) parallel. In both cases, our simulations show that due to the drastically reduced convection speed in the slow and dense heavy ion plasma near Titan, the satellite carries a bundle of “fossilized” magnetic field lines from the magnetosphere in the magnetosheath. Furthermore, the passage through Saturn''s magnetopause goes along with a disruption of Titan''s pick-up tail. Although the tail is not detached from the satellite, large clouds of heavy ion plasma are stripped of its outer flank, featuring a wave-like pattern. Whereas in case (B) under parallel flow conditions there is only a small retardation of about 5min between the passage of Titan through the magnetopause and the reconfiguration of the pick-up tail, the tail reconfiguration in the case (A) scenario is completed not until 25min after the magnetopause passage. The lifetime of fossil fields in the moon''s ionosphere is approximately 25min, regardless of whether parallel or antiparallel flow conditions are applied. [Copyright &y& Elsevier]

Abstract: We present new results concerning electron temperature (T e ) mapping in the inner magnetosphere of Saturn (<7RS). The data are obtained by the Langmuir Probe (LP) instrument of the Radio and Plasma Wave Science (RPWS) investigation on board Cassini. The study is based on the fourteen first orbits around Saturn, and focus is on cold (<10eV) and dense (>5cm−3) electron populations in the inner plasma torus (plasma disc). Apart from a general increase with distance from Saturn and away from the equatorial plane (latitude), we identify a possibly anisotropic electron temperature in the plasma disc, as well as the presence of photoelectrons from the spacecraft or E-ring dust particles. A polytropic index of γ≈+0.4 is determined from the observations, which can be used in theoretical models of the plasma disc. We also infer local variations in T e near the equatorial plane, where the E-ring of dusty plasma and enhancements of water rich neutral gas exist, and determine constraints on the energy source required to heat the electrons in the plasma disc. We suggest that Joule heating or heating by low-frequency plasma waves as well as cooling by neutral gas and E-ring dust are involved in the energy balance, together with Coulomb collision heating by co-rotating ions. [Copyright &y& Elsevier]

Abstract: We present the two-stage method used to calibrate the electron spectrometer (ELS), part of the plasma spectrometer (CAPS) on board the Cassini spacecraft currently in orbit around Saturn. The CAPS-ELS is a top-hat electrostatic analyser designed to measure electron fluxes between 0.5eV and 26keV. The on-ground calibration method described here includes the production of photoelectrons, which are energised and passed into the CAPS-ELS in a purpose designed calibration facility. Knowledge of the intensity of these incident electrons and the subsequent instrument output provides an on-ground calibrated geometric factor. Comparative studies of physical quantities such as plasma density and electron differential flux calculated using on-ground calibration factor with the quantities deduced from the wave experiment and high energy electron detector provide in-flight calibration. The results of this are presented together with a comparison of the experimentally calibrated values with simulated calibration values. [Copyright &y& Elsevier]

The article presents a reflection on the way that the Earth was conceived in the 18th century in terms of surface, shape and size. Information on the scientific mission of Cayenne, French Guiana, in 1672, concerning observations regarding the position of the Sun and Moon and atmospheric details, is provided. The significant evolution in the conception of the Earth that occurred in the 18th century is analyzed. The revolution that the work of English physicist Isaac Newton created in France at this period is discussed.

Abstract: We study the interaction of Saturn''s small, icy moon Enceladus and its plume with the corotating magnetospheric plasma by means of a 3D hybrid simulation model, which treats the ions as individual particles and the electrons as a massless, charge-neutralizing fluid. We analyze systematically how Enceladus’ internal conductivity and plasma absorption at the surface as well as charge exchange and pick-up in the plume contribute to the overall structure of the interaction region. Furthermore, we provide a comparison of our simulation results to data obtained by the Cassini magnetometer instrument. The major findings of this study are: (1) the magnetic field diffuses through the solid body of Enceladus almost unaffected, whereas plasma absorption gives rise to a symmetric depletion wake downstream of the moon; (2) due to the small gyroradii of the newly generated plume ions, the pick-up tail possesses a 2D structure; (3) the magnetic field lines drape around the plume, which triggers an Alfvén wing system that dominates the structure of Enceladus’ plasma environment. Inside the plume itself, a magnetic cavity is formed; (4) besides the reproduction of the key features of the observed magnetic field signatures, evidence for variability in the locations of the active jets and in the total gas content of the plume are shown. [Copyright &y& Elsevier]

Abstract: In this paper Saturn''s nightside and pre-dawn electron (0.5eV–28keV) plasma sheet is studied using Cassini plasma electron and magnetic field data from 2006. Case studies are presented which exemplify the typical and atypical states of the plasma sheet, and are complemented by a statistical study of the plasma sheet. It will be shown that Saturn''s nightside and pre-dawn electron plasma sheet exists in two states: a quiescent state with a steady electron temperature of and where the electron distribution functions are best characterised by Kappa distributions, and a disturbed state where the electrons are hot and often seen in alternating layers between warm and hot populations. Evidence is also presented for bimodal cold/warm (both quiet and disturbed states) and warm/hot distributions (disturbed states). The disturbed states are qualitatively similar to electron distributions from Earth''s magnetotail during intervals of reconnection and we argue that these disturbed states also result from periods of tail reconnection. We present statistics of electron number density, temperature, partial electron beta, and pressure, and show that large values of partial beta are necessary but not sufficient to uniquely identify the central plasma sheet. Finally the thermodynamic properties of the electron plasma sheet are studied and we show that the electrons behave isothermally. These results are important for modelling and theoretical analyses, and for use in studies which examine dynamics in Saturn''s magnetosphere. [Copyright &y& Elsevier]

Abstract: This is a data paper designed to facilitate the use of and comparisons to Cassini/visual and infrared mapping spectrometer (VIMS) spectral mapping data of Saturn''s moon Titan. We present thumbnail orthographic projections of flyby mosaics from each Titan encounter during the Cassini prime mission, 2004 July 1 through 2008 June 30. For each flyby we also describe the encounter geometry, and we discuss the studies that have previously been published using the VIMS dataset. The resulting compliation of metadata provides a complementary big-picture overview of the VIMS data in the public archive, and should be a useful reference for future Titan studies. [Copyright &y& Elsevier]

Abstract: The data obtained by the Cassini Radio and Plasma Wave Science (RPWS) instrument during the shallow (17.02.2005) and the steep (14.07.2005) crossings of the E-ring revealed a considerable electron depletion in proximity to Enceladus''s orbit (the difference between the ion and electron densities can reach ). Assuming that this depletion is a signature of the presence of charged dust particles, the main characteristics of dust down to submicron sized particles are derived. The differential size distribution is found to be well described by a power law with an index for the lower size limit and for . The calculated average integral dust number density is weakly affected by values of and . For , both flybys gave the maximum dust density about in the vicinity of Enceladus. Our results imply that the dust structure near Enceladus is characterized by approximately the same vertical length scale of 8000km and reaches a maximum at the same radial distance (displaced outward of the orbit of Enceladus) as found by Kempf et al. [2008. The E-ring in the vicinity of Enceladus. Spatial distribution and properties of the ring particles. Icarus 193, 420–437], from the dust impact data. [Copyright &y& Elsevier]

Abstract: During its tour Cassini has observed numerous plasma injection events in Saturn''s inner magnetosphere. Here, we present a case study of one “young” plasma bubble observed when Cassini was in the equatorial plane. The bubble was observed in the equatorial plane at ∼7 Saturn radii from Saturn and had a maximum azimuthal extent of ∼0.25Rs (Rs=Saturn radius ∼60330km). We show that the electron density inside the event is lower by a factor ∼3 and the electron temperature higher by over an order of magnitude compared to its surroundings. The injection contains slightly increased magnetic field magnitude of 49nT compared with a background field of 46nT. Modelling of pitch angle distributions inside the plasma bubble and measurements of plasma drift provide a novel way to estimate that the bubble originated between 9

Abstract: We present observational evidence that the ionosphere of Titan below an altitude of 1150km is a significant source of heavy (>100amu) molecular organic species. This study is based on measurements by five instruments (RPWS/LP, RPWS/E, INMS, CAPS/ELS, CAPS/IBS) onboard the Cassini spacecraft during three flybys (T17, T18, T32) of Titan. The ionospheric peaks encountered at altitudes of 950–1300km had densities in the range 900–3000cm−3. Below these peaks the number densities of heavy positively charged ions reached 100–2000cm−3 and approached 50–70% of the total ionospheric density with an increasing trend toward lowest measured altitudes. Simultaneously measured negatively charged ion densities were in the range 50–150cm−3. These results imply that ~105–106 heavy positively charged ions/m3/s are continuously recombining into heavy neutrals and supply the atmosphere of Titan. The ionosphere may in this way produce 0.1–1Mt/yr of heavy organic compounds and is therefore a sizable source for aerosol formation. We also predict that Titan''s ionosphere is dominated by heavy (>100amu) molecular ions below 950km. [Copyright &y& Elsevier]

Abstract: We present the first results of ionospheric conductivities at Titan based on measurements during 17 Titan flybys from the Cassini spacecraft. We identify an ionospheric region ranging from (approximately the location of the exobase) to approximately 1000km where electrical currents perpendicular to the magnetic field may become important. In this region the ionosphere is highly conductive with peak Pedersen conductivities of 0.002–0.05S/m and peak Hall conductivities of 0.01–0.3S/m depending on Solar illumination and magnetospheric conditions. Ionospheric conductivities are found to be typically higher on the sunlit side of Titan. However, Hall and Pedersen conductivities depend strongly on the magnetic field magnitude which is highly variable, both in altitude and with respect to the draping configuration of Saturn''s magnetic field around Titan. Furthermore, a consistent double peak nature is found in the altitude profile of the Pedersen conductivity. A high altitude peak is found to be located between 1300 and 1400km. A second and typically more conductive region is observed below 1000km, where the magnetic field strength drops sharply while the electron density still remains high. This nature of the Pedersen conductivity profile may give rise to complicated ionospheric–atmospheric dynamics and may be expected also at other unmagnetized objects with a substantial atmosphere, such as e.g. Mars and Venus. Estimates of the total Pedersen conductance are found to range between 1300 and 22,000S. The Pedersen conductance is always higher than the local Alfvén conductance but the difference varies by two orders of magnitude (from a factor 4 to 100). Thus, the conditions for reflection or absorption of Alfvén waves in Titans ionosphere are highly variable and depends strongly on the magnetic field strength. [Copyright &y& Elsevier]

Abstract: In this study we present data from 17 Titan flybys showing that solar photons are the main ionisation source of Titan''s dayside atmosphere. This is the first comprehensive study of Solar Zenith Angle (SZA) dependence of the electron number density and electron temperature at the ionospheric peak. The results show on average four times more plasma on the dayside compared to the nightside, with typical dayside electron densities of around 2500– and corresponding nightside densities of around 400–. We identify a broad transition region between SZA and , where the ionosphere of Titan changes from being entirely sunlit to being in the shadow of the moon. For SZA the ionisation peak altitude increases with increasing SZA, whereas the transition region and the nightside show more scattered ionospheric peak altitudes. Typical electron temperatures at the ionospheric peak are 0.03–0.06eV (–700K) for both dayside and nightside. [Copyright &y& Elsevier]

Abstract: We present several independent in-situ measurements, which provide evidence that charged dust in the E-ring interacts collectively with the dense surrounding plasma disk of Saturn, i.e., form a system of dust-plasma interaction. The results are based on data sampled by the Radio and Plasma Wave Science (RPWS) investigation onboard Cassini, which allows for interferometry of plasma density inhomogeneities (δn/n) with two antenna elements and a Langmuir probe sensor. The interferometer experiment detects two ion populations; one co-rotating with the planetary magnetic field and another moving with near Keplerian speed around Saturn. The full range of RPWS measurements indicates that the Keplerian population consists of colder ions (T i

Abstract: The intensity of H Ly (2P–1S) and OI () is mapped in the magnetosphere of Saturn using the ultraviolet imaging spectrograph (UVIS) [Esposito, L.W., Barth, C.A., Colwell, J.E., Lawrence, G.M., McClintock, W.E., Stewart, A.I.F., Keller, H.U., Korth, A., Lauche, H., Festou, M.C., Lane, A.L., Hansen, C.J., Maki, J.N., West, R.A., Jahn, H., Reulke, R., Warlich, K., Shemansky, D.E., Yung, Y.L., 2004. The Cassini ultraviolet imaging spectrograph investigation. Space Science Reviews 115, 299–361] onboard Cassini. Spatial coverage is built up by stepping the slit sequentially across the system (system scan). Data are obtained at a large range of space-craft–Saturn distances. The observed atomic hydrogen distribution is very broad, extending beyond in the equatorial plane, with the intensity increasing with decreasing distances to Saturn. The distribution displays persistent local-time asymmetries, and is seen connecting continuously to the upper atmosphere of the planet at sub-solar latitudes located well outside of the equatorial (ring) plane. This is consistent with the source of the atomic hydrogen being located at the top of the atmosphere on the sun-lit side of the planet on the southern hemisphere. In addition there are a number of temporally persistent features in the intensity distribution, indicating a complex hydrogen energy distribution. The emission from OI is generally distributed as a broad torus centered around although the position of the peak intensity can vary by as much as . There is significant intensity present out to . HST observations of hydroxyl (OH) are re-analyzed and display a distribution half as broad as that of oxygen, also centered at . The observed atomic oxygen distribution requires a sourcing of against loss due to charge capture with the plasma. Using the ion partitioning of Schippers et al. [2008. Multi-instrument analysis of electron populations in Saturn''s magnetosphere. Journal of Geophysical Research (Space Physics) 113 (A12) 7208–+] then recombination of and will account for about a quarter of the mass-loss in the inner magnetosphere, with charge capture of accounting for the rest. The oxygen loss rate is seen to vary by over periods of weeks. [Copyright &y& Elsevier]

Abstract: Saturn''s largest moon, Titan, provides an interesting opportunity to study how dense atmospheres interact with the surrounding plasma environment. Without an intrinsic magnetic field, this satellite''s nitrogen-rich atmosphere is relatively unprotected from plasma interactions. Therefore, the energy-deposition rate is important for understanding chemistry and dynamics in Titan''s atmosphere. Since the plasma environment can vary significantly we focus here on the T18 Titan encounter using in-situ data from instruments on board the Cassini spacecraft. These instruments cannot provide in-situ information below the spacecraft closest approach altitude (∼>960km) so we use the Cassini magnetospheric imaging instrument (MIMI) ion-neutral camera (INCA) to remotely image energetic hydrogen particle fluxes (20–80keV) at altitudes below Titan closest approach. We also use the MIMI low-energy magnetosphere measurements system (LEMMS) to measure the incident ion fluxes as the spacecraft approaches Titan and combine these data sets with an atmospheric model to first reproduce INCA images. We then use this model to calculate the energy-deposition profiles for the observed incident proton flux. Our model is able to reproduce the INCA observations and give the energy density deposited vs. altitude in Titan''s atmosphere; however, we find that the incident fluxes and energy-deposition profiles vary significantly during the encounter. [Copyright &y& Elsevier]

Abstract: NASA''s Cassini project has conducted a series of innovative “Scientist for a Day” outreach sessions with great success. Individual students and classrooms are presented, via the Cassini web site, with a selection of images that could be taken by the Cassini spacecraft in orbit around Saturn. Student essays are submitted indicating their preferred image, along with a detailed description of why that image was selected, often drawing heavily from material found elsewhere in the Cassini web resources. Winners from different age categories are chosen, and the selected images are sequenced. Very soon after the images reach the ground, winning classrooms are invited to participate via tele- and video-con with key Cassini scientists and engineers, where interactive discussions take place. This program has been very successful and is considered a key outreach highlight of Cassini and JPL in general. It reaches a significant number of students, involves them directly in image planning, and engages them in a highly interactive and inspirational environment requiring detailed study and creative thought. [Copyright &y& Elsevier]

Abstract: The Chemical Analyser subsystem of the Cosmic Dust Analyser (CDA) aboard the Cassini spacecraft performs in situ measurements of the chemical composition of dust in space. The instrument records time-of-flight mass spectra of cations, extracted from the impact cloud that is created by high-velocity particle impacts onto the detector target. Thus, the spectra not only show signals of particle components but also of ions from the target material and target contamination. The aim of this work is to determine which non-particle ions are to be expected in the spectra obtained in space operation at Saturn. We present an analysis of the contamination state of the instrument''s impact target. Beside investigations of the purity of the rhodium target surface, spectra from CDA calibration experiments at the dust accelerator facility are evaluated with regard to contamination signatures. Furthermore, contamination mass lines in spectra obtained by impacts of Jovian and Saturnian dust stream particles are analysed. Due to their small size and high speed, stream particle impacts predominantly produce ions from the target material and therefore the spectra are excellent probes of the contamination state of the target operating in space. With the exception of adsorbed hydrogen and carbon, the level of contamination is very low. Implications for CDA spectra of Saturnian E ring particle impacts are derived. The findings confirm the published interpretations. The low level of alkali metal contamination implies a significant sodium contribution in the composition of E ring ice particles. Additionally, ionisation thresholds for the occurrence of contamination mass lines can be utilised to set limits for the impact velocity. [Copyright &y& Elsevier]

This report presents both a retrospective of ground-based support for spacecraft missions to the outer solar system and a perspective of support for future missions. Past support is reviewed in a series of case studies involving the author. The most basic support is essential, providing the mission with information without which the planned science would not have been accomplished. Another is critical, without which science would have been returned, but missing a key element in its understanding. Some observations are enabling by accomplishing one aspect of an experiment which would otherwise not have been possible. Other observations provide a perspective of the planet as a whole which is not available to instruments with narrow fields of view and limited spatial coverage, sometimes motivating a re-prioritizing of experiment objectives. Ground-based support is also capable of providing spectral coverage not present in the complement of spacecraft instruments. Earth-based observations also have the capability of filling in gaps of spacecraft coverage of atmospheric phenomena, as well as providing surveillance of longer-term behavior than the coverage available to the mission. Future missions benefiting from ground-based support would include the Juno mission to Jupiter in the next decade, a flagship-class mission to the Jupiter or to the Saturn systems currently under consideration, and possible intermediate-class missions which might be proposed in NASA’s New Frontiers category. One of the principal benefits of future 30 m-class giant telescopes would be to improve the spatial resolution of maps of temperature and composition which are derived from observations of thermal emission at mid-infrared and longer wavelengths. In many situations, this spatial resolution is competitive with those of the relevant instruments on the spacecraft themselves. [ABSTRACT FROM AUTHOR]

The first century of telescopic astronomy can be divided into two periods. During the first, from 1609 to ca. 1640, observations were made with a simple “Dutch” or “Galilean” telescope with a concave eyepiece. Galileo made all his discoveries with this instrument. Its limited field of view, however, made magnifications of more than about 20 impractical, and therefore this instrument’s limit had been reached within a few years. During the second period, ca. 1640–ca. 1700, the simple astronomical telescope came into use, almost immediately augmented with a field lens and an erector lens (the latter used only for terrestrial purposes). Magnifications were increased by increasing the focal lengths of objectives, and this quickly led to very long telescopes, often used without a tube. The astronomical discoveries made possible by this form of the instrument were, however, made with instruments of relatively modest lengths. By the end of the century, very long telescopes fell out of use, while shorter ones were adapted for measurements. Further discoveries became possible only with the reflecting telescope in the second half of the eighteenth century. [ABSTRACT FROM AUTHOR]

Abstract: Data from the Cassini plasma spectrometer (CAPS) electron spectrometer (ELS) have been found to be contaminated with an energy-independent background count rate which has been associated with radiation sources on Cassini. In this paper we describe this background radiation and quantitatively assess its impact on numerically integrated electron moments. The general properties of such a background and its effects on numerical moments are derived. The properties of the ELS background are described and a model for the background presented. A model to generate synthetic ELS spectra is presented and used to evaluate the density and temperature of pure noise and then extended to include ambient distributions. It is shown that the presence of noise produces a saturation of the electron density and temperature at quasi-constant values when the instrument is at background, but that these noise level moments are dependent on the floating spacecraft potential and the orientation of the ELS instrument with respect to the spacecraft. When the ambient distribution has a poor signal-to-noise ratio (SNR) the noise determines the density and temperature; however, as the SNR increases (increasing primarily with density) the density and temperature tend to those of the ambient distribution. It is also shown that these noise effects produce highly artificial density–temperature inverse correlations. A method to subtract this noise is presented and shown to correct for the presence of the noise. Simulated error estimates for the density and temperature are also presented. The analysis described in this paper not only applies to weak background noise, but also to more significant penetrating backgrounds such as those in radiation belt regions of planetary magnetospheres. [Copyright &y& Elsevier]

The Cassini RADAR is a multimode instrument used to map the surface of Titan, the atmosphere of Saturn, the Saturn ring system, and to explore the properties of the icy satellites. Four different active mode bandwidths and a passive radiometer mode provide a wide range of flexibility in taking measurements. The scatterometer mode is used for real aperture imaging of Titan, high-altitude (around 20 000 km) synthetic aperture imaging of Titan and Iapetus, and long range (up to 700 000 km) detection of disk integrated albedos for satellites in the Saturn system. Two SAR modes are used for high- and medium-resolution (300-1000 m) imaging of Titan's surface during close flybys. A high-bandwidth altimeter mode is used for topographic profiling in selected areas with a range resolution of about 35 m. The passive radiometer mode is used to map emission from Titan, from Saturn's atmosphere, from the rings, and from the icy satellites. Repeated scans with differing polarizations using both active and passive data provide data that can usefully constrain models of surface composition and structure. The radar and radiometer receivers show very good stability, and calibration observations have provided an absolute calibration good to about 1.3 dB. Relative uncertainties within a pass and between passes can be even smaller. Data are currently being processed and delivered to the planetary data system at quarterly intervals one year after being acquired. [ABSTRACT FROM AUTHOR]

Abstract: The Cassini Imaging Science Subsystem (ISS) acquired 282, 258, and 513 high-resolution images (<800m/pixel) of Mimas, Tethys, and Iapetus, respectively, during two close flyby of Tethys and Iapetus and eight non-targeted flybys between 2004 and 2007. We combined these images with lower-resolution Cassini images and others taken by Voyager cameras to produce high-resolution semi-controlled mosaics of Mimas, Tethys, and Iapetus. These global mosaics are the baseline for high-resolution Mimas and Iapetus maps and a Tethys atlas. The nomenclature used in these maps was proposed by the Cassini imaging team and was approved by the International Astronomical Union (IAU). The two maps and the atlas are available to the public through the Imaging Team''s website [http://ciclops.org/maps] and the Planetary Data System [http://pds.jpl.nasa.gov]. [Copyright &y& Elsevier]