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To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2009.04.025 Byline: T.A. Hurford (a), B.G. Bills (b)(c), P. Helfenstein (d), R. Greenberg (e), G.V. Hoppa (f), D.P. Hamilton (g) Keywords: Tectonics; Enceladus Abstract: Given the non-spherical shape of Enceladus [], the satellite will experience gravitational torques that will cause it to physically librate as it orbits Saturn. Physical libration would produce a diurnal oscillation in the longitude of Enceladus' tidal bulge, which could have a profound effect on the diurnal tidal stresses experienced by the surface of the satellite. Although Cassini ISS has placed an observational upper limit on the amplitude of Enceladus' libration, smaller amplitudes can still have geologically significant consequences. Here we present the first detailed description of how physical libration affects tidal stresses and how those stresses might then affect geological processes including crack formation and propagation, south polar eruption activity, and tidal heating. Our goal is to provide a framework for testing the hypothesis that geologic features on Enceladus are produced by tidal stresses from diurnal librations of the satellite. Author Affiliation: (a) Planetary Systems Laboratory, NASA Goddard Spaceflight Center, Greenbelt, MD 20771, USA (b) Jet Propulsion Laboratory, Pasadena, CA 90119, USA (c) Institute for Geophysics and Planetary Physics, Scripps Institution of Oceanography, La Jolla, CA 92093, USA (d) CRSR, Cornell University, Ithaca, NY 14853, USA (e) Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ 85721, USA (f) Raytheon, Woburn, MA 01801, USA (g) Department of Astronomy, University of Maryland, College Park, MD 20742, USA Article History: Received 20 October 2008; Revised 16 March 2009; Accepted 17 April 2009

Identical in situ dust detectors are flown on board the Galileo and Ulysses spacecraft. They record impacts of micrometeoroids in the ecliptic plane at heliocentric distances from 0.7 to 5.4 AU and in a plane almost perpendicular to the ecliptic from -79 [degrees] to +79 [degrees] ecliptic latitude. The combination of both Ulysses and Galileo measurements yields information about the radial and latitudinal distributions of micron- and submicron-sized dust in the Solar System. Two types of dust particles were found to dominate the dust flux in interplanetary space. Interplanetary micrometeoroids covering a wide mass range from [10.sup.-16] to [10.sup.-6] g are recorded mostly inside 3 AU and at latitudes below 30 [degrees]. Interstellar grains with masses between [10.sup.-14] and [10.sup.-12] g have been positively identified outside 3 AU near the ecliptic plane and outside 1.8 AU at high ecliptic latitudes (>50 [degrees]). Interstellar grains move on hyperbolic trajectories through the planetary system and constitute the dominant dust flux (1.5 x [10.sup.-4] [m.sup.-2] [sec.sup.-1]) in the outer Solar System and at high ecliptic latitudes. To compare and analyze the Galileo and Ulysses data sets, a new model is developed based on J. Geophys. Res. 98, 17029-17048, Divine's (1993, 'five populations of interplanetary meteoroids' model. Both models describe the interplanetary meteoroid environment in terms of dust populations on distinct orbits. Taking into account the measured velocities and the effect of radiation pressure on small particles (described by the ratio of radiation pressure force to gravity, [Beta]), we define four populations of meteoroids on elliptical orbits and one population on hyperbolic orbit that can fit the micrometeoroid flux observed by Galileo and Ulysses. Micrometeoroids with masses greater than [10.sup.-10] g and negligible radiation pressure ([Beta] = 0) orbit the Sun on low to moderately eccentric orbits and with low inclinations ([less than or equal to] 30 [degrees]). Populations of smaller particles with mean masses of [10.sup.-11] g ([Beta] = 0.3), [10.sup.-13] g ([Beta] = 0.8), and 5 x [10.sup.-15] g ([Beta] = 0.3), respectively, have components with high eccentricities and have increasingly wider inclination distributions with decreasing mass. Similarities among the orbit distributions of the small particle populations on bound orbits suggest that all are genetically related and are part of an overall micrometeoroid complex that prevails in the inner Solar System. The high-eccentricity component of the small particle populations may actually be [Beta]-meteoroids which are not well characterized by our measurements. Our modeling suggests further that the interstellar dust flux is not reduced at Ulysses' perihelion distance (1.3 AU) and that it contributes about 30% of the total dust flux observed there.

The Galileo Dust Detection System (DDS) detected a population of micron-sized grains in and amongst the orbits of Io, Europa, Ganymede and Callisto. Previous studies, using roughly 50% of the data now available, concluded that the dominant sources for the impacts were magnetospherically captured interplanetary particles largely on retrograde orbits ( Colwell et al., 1998b; Thiessenhusen et al., 2000 ) and impact-generated ejecta from the Galilean satellites ( Krüger et al., 1999b; Krivov et al., 2002a ). Here we revisit the problem with the full data set and broaden our consideration to include four additional source populations: debris from the outer satellites, interplanetary and interstellar grains and particles accelerated outwards from Io and the jovian rings. We develop a model of detectable orbits at each Galileo position and we find that about 10% of the impact data require non-circular orbits with eccentricities greater than 0.1. In addition, ~3% of impacts require orbital solutions with eccentricities in excess of 0.7. Using the spatial distribution of particles, we are able to exclude, as dominant sources, all the additional source populations except for outer satellite particles. A study of DDS directional information demonstrates that none of the six standard sources fit the data well and thus a combination of sources is necessary. There are insufficient data to uniquely identify the relative strengths of the various contributions. However, we find an excess of large particles that is consistent with retrograde trajectories. [ABSTRACT FROM AUTHOR]

In January 2000, there was a record maximum rainfall throughout much of the watershed of the Swan River estuary. Within three weeks of this rainfall event, a large, mono-specific bloom of the cyanobacterium Microcystis aeruginosa had developed in the estuary, with cell counts peaking at over 100,000 cells ml−1. A three-dimensional, coupled hydrodynamic–ecological model, ELCOM-CAEDYM, was applied to the period of development and subsequent decline of the bloom. The model, previously calibrated for more typical years (1995 and 1996) when there was no bloom, accurately reproduced the unusual hydrodynamic conditions in the estuary as well as the approximate magnitude and timing of the M. aeruginosa bloom. The model results supported the hypothesis that salinity and temperature are the primary factors controlling the growth of M. aeruginosa during the period of interest. The simulations described in this study show how the model captures the complex interactions between the physical and biogeochemical environment, and indicate the usefulness of the model as a predictive management tool. [Copyright &y& Elsevier]

Agriculture is a major contributor to marine nitrogen pollution, and treatment wetlands can be a strategy to reduce it. However, few studies have assessed the potential of treatment wetlands to mitigate nitrogen pollution in tropical regions. We quantify the nitrogen removal rates of four recently constructed treatment wetlands in tropical Australia. We measured denitrification potential (D t), the inflow-outflow of nutrients, and tested whether the environment in these tropical catchments is favourable for nitrogen removal. D t was detected in three of the four systems with rates between 2.0 and 12.0 mg m-2 h−1; the highest rates were measured in anoxic soils (ORP −100 to 300 mV) that were rich in carbon and nitrogen (>2% and >0.2%, respectively). The highest nitrogen removal rates were measured when NO 3 −-N concentrations were >0.4 mg L−1 and when water flows were slow. Treatment wetlands in tropical regions can deliver high removal rates of nitrogen and other pollutants when adequately managed. This strategy can reduce nutrient loads and their impacts on sensitive coastal zones such as the Great Barrier Reef. [ABSTRACT FROM AUTHOR]

• In order to better predict and manage cyanoHABs in a changing world, researchers need to leverage studies undertaken to date. • There is a need for experiments, observations, and models which capture both eutrophication and a changing climate. • There are also emerging species of concern, e.g. benthic cyanobacteria, which require more detailed study. Harmful cyanobacterial blooms (=cyanoHABs) are an increasing feature of many waterbodies throughout the world. Many bloom-forming species produce toxins, making them of particular concern for drinking water supplies, recreation and fisheries in waterbodies along the freshwater to marine continuum. Global changes resulting from human impacts, such as climate change, over-enrichment and hydrological alterations of waterways, are major drivers of cyanoHAB proliferation and persistence. This review advocates that to better predict and manage cyanoHABs in a changing world, researchers need to leverage studies undertaken to date, but adopt a more complex and definitive suite of experiments, observations, and models which can effectively capture the temporal scales of processes driven by eutrophication and a changing climate. Better integration of laboratory culture and field experiments, as well as whole system and multiple-system studies are needed to improve confidence in models predicting impacts of climate change and anthropogenic over-enrichment and hydrological modifications. Recent studies examining adaptation of species and strains to long-term perturbations, e.g. temperature and carbon dioxide (CO 2) levels, as well as incorporating multi-species and multi-stressor approaches emphasize the limitations of approaches focused on single stressors and individual species. There are also emerging species of concern, such as toxic benthic cyanobacteria, for which the effects of global change are less well understood, and require more detailed study. This review provides approaches and examples of studies tackling the challenging issue of understanding how global changes will affect cyanoHABs, and identifies critical information needs for effective prediction and management. [ABSTRACT FROM AUTHOR]

Abstract: The Galileo spacecraft was the first man-made satellite of Jupiter, orbiting the planet between December 1995 and September 2003. The spacecraft was equipped with a highly sensitive dust detector that monitored the jovian dust environment between approximately 2 and 370 R J (jovian radius R J=71492km). The Galileo dust detector was a twin of the one flying on board the Ulysses spacecraft. This is the tenth in a series of papers dedicated to presenting Galileo and Ulysses dust data. Here we present data from the Galileo dust instrument for the period January 2000 to September 2003 until Galileo was destroyed in a planned impact with Jupiter. The previous Galileo dust data set contains data of 2883 particles detected during Galileo''s interplanetary cruise and 12978 particles detected in the jovian system between 1996 and 1999. In this paper we report on the data of additional 5389 particles measured between 2000 and the end of the mission in 2003. The majority of the 21250 particles for which the full set of measured impact parameters (impact time, impact direction, charge rise times, charge amplitudes, etc.) was transmitted to Earth were tiny grains (about 10nm in radius), most of them originating from Jupiter''s innermost Galilean moon Io. They were detected throughout the jovian system and the impact rates frequently exceeded 10min−1. Surprisingly large impact rates up to 100min−1 occurred in August/September 2000 when Galileo was far away from Jupiter, implying dust ejection rates in excess of 100kgs−1. This peak in dust emission appears to coincide with strong changes in the release of neutral gas from the Io torus. Strong variability in the Io dust flux was measured on timescales of days to weeks, indicating large variations in the dust release from Io or the Io torus or both on such short timescales. Galileo has detected a large number of bigger micron-sized particles mostly in the region between the Galilean moons. A surprisingly large number of such bigger grains was measured in March 2003 within a four-day interval when Galileo was outside Jupiter''s magnetosphere at approximately 350 R J jovicentric distance. Two passages of Jupiter''s gossamer rings in 2002 and 2003 provided the first actual comparison of in-situ dust data from a planetary ring with the results inferred from inverting optical images. Strong electronics degradation of the dust instrument due to the harsh radiation environment of Jupiter led to increased calibration uncertainties of the dust data. [Copyright &y& Elsevier]

Abstract: The Ulysses spacecraft has been orbiting the Sun on a highly inclined ellipse (, perihelion distance 1.3AU, aphelion distance 5.4AU) since it encountered Jupiter in February 1992. Since then it has made almost three revolutions about the Sun. Here we report on the final three years of data taken by the on-board dust detector. During this time, the dust detector recorded 609 dust impacts of particles with masses , bringing the mission total to 6719 dust data sets. The impact rate varied from a low value of 0.3 per day at high ecliptic latitudes to 1.5 per day in the inner solar system. The impact direction of the majority of impacts between 2005 and 2007 is compatible with particles of interstellar origin; the rest are most likely interplanetary particles. We compare the interstellar dust measurements from 2005/2006 with the data obtained during earlier periods (1993/1994) and (1999/2000) when Ulysses was traversing the same spatial region at southern ecliptic latitudes but the solar cycle was at a different phase. During these three intervals the impact rate of interstellar grains varied by more than a factor of two. Furthermore, in the two earlier periods the grain impact direction was in agreement with the flow direction of the interstellar helium while in 2005/2006 we observed a shift in the approach direction of the grains by approximately away from the ecliptic plane. The reason for this shift remains unclear but may be connected with the configuration of the interplanetary magnetic field during solar maximum. We also find that the dust measurements are in agreement with the interplanetary flux model of which was developed to fit a 5-year span of Ulysses data. [Copyright &y& Elsevier]

Abstract: The dust detector system on board the Galileo spacecraft recorded dust impacts in circumjovian space during the craft''s orbital mission about Jupiter. This is the eighth in a series of papers dedicated to presenting Galileo and Ulysses dust data. We present data from the Galileo dust instrument for the period January 1997–December 1999 when the spacecraft completed 21 revolutions about Jupiter. In this time interval data were obtained as high resolution realtime science data or recorded data during 449 days (representing 41% of the entire period), or via memory readouts during the remaining times. Because the data transmission rate of the spacecraft was very low, the complete data set (i.e. all parameters measured by the instrument during impact of a dust particle) of only 3% (7625) of all particles detected could be transmitted to Earth; the other particles were only counted. Together with the data of 2883 particles detected during Galileo''s interplanetary cruise and 5353 particles detected in the jovian system in 1996, complete data of 15861 particles detected by the Galileo dust instrument from 1989 to 1999 are now available. The majority of the detected particles were tiny grains (about 10nm in radius), most of them originating from Jupiter''s innermost Galilean moon Io. They were detected throughout the jovian system and the highest impact rates exceeded (C21 orbit; 01 July 1999). With the new data set the times of onset, cessation and a shift in the impact direction of the grains measured during 19 Galileo orbits about Jupiter are well reproduced by simulated 9nm particles charged up to a potential of , confirming earlier results obtained for only two Galileo orbits (Horányi, M., Grün, E., Heck, A., 1997. Modeling the Galileo dust measurements at Jupiter. Geophys. Res. Lett. 24, 2175–2178). Galileo has detected a large number of bigger particles mostly in the region between the Galilean moons. The average radius of 370 of these grains measured in the 1996–1999 period is about (assuming spherical grains with density ) and the size distribution rises steeply towards smaller grains. The biggest detected particles have a radius of about . [Copyright &y& Elsevier]

Abstract: The Ulysses spacecraft has been orbiting the Sun on a highly inclined ellipse (, perihelion distance 1.3AU, aphelion distance 5.4AU) since it encountered Jupiter in 1992. Between January 2000 and December 2004, the spacecraft completed almost an entire revolution about the Sun, passing through perihelion in May 2001 and aphelion in July 2004. In this five-year period the dust detector on board recorded 4415 dust impacts. We publish and analyse the complete data set of both raw and reduced data for particles with masses . Together with 1695 dust impacts recorded between launch of Ulysses and the end of 1999 published earlier (Grün, E., Baguhl, M., Divine, N., Fechtig, H., Hamilton, D.P, Hanner, M.S., Kissel, J., Lindblad, B.A., Linkert, D., Linkert, G., Mann, I., McDonnell, J.A.M., Morfill, G.E., Polanskey, C., Riemann, R., Schwehm, G.H., Siddique, N., Staubach, P., Zook, H.A., 1995a. Two years of Ulysses dust data. Planetary Space Sci. 43, 971–999, Paper III; Krüger, H., Grün, E., Landgraf, M., Baguhl, M., Dermott, S.F., Fechtig, H., Gustafson, B.A., Hamilton, D.P., Hanner, M.S., Horányi, M., Kissel, J., Lindblad, B., Linkert, D., Linkert, G., Mann, I., McDonnell, J.A.M., Morfill, G.E., Polanskey, C., Schwehm, G.H., Srama, R., Zook, H.A., 1995. Three years of Ulysses dust data: 1993 to 1995. Planetary and Space Sci. 47, 363–383, Paper V; Krüger, H., Grün, E., Landgraf, M., Dermott, S.F., Fechtig, H., Gustafson, B.A., Hamilton, D.P., Hanner, M.S., Horányi, M., Kissel, J., Lindblad, B., Linkert, D., Linkert, G., Mann, I., McDonnell, J.A.M., Morfill, G.E., Polanskey, C., Schwehm, G.H., Srama, R., Zook, H.A., 2001b. Four years of Ulysses dust data: 1996 to 1999. Planetary Space Sci. 49, 1303–1324, Paper VII), a data set of 6110 dust impacts detected with the Ulysses sensor between October 1990 and December 2004 is now available. The impact rate measured between 2000 and 2002 was relatively constant with about 0.3 impacts per day showing a maximum at 1.5 per day around ecliptic plane crossing in early-2001. The impact direction of the majority of impacts between 2000 and 2002 is compatible with particles of interstellar origin, the rest are most likely interplanetary particles. In 2003 and 2004 dust stream particles originating from the jovian system dominated the overall impact rate. Twenty-two individual dust streams were measured between November 2002 and December 2004. The observed impact rates are compared with models for interplanetary and interstellar dust. The dust measurements from the entire mission since Ulysses launch give good agreement with the interplanetary flux model of Staubach, P., Grün, E., Jehn, R., 1997. The meteoroid environment near Earth, Adv. Space Res. 19, 301–308. [Copyright &y& Elsevier]