The tectonic patterns and stress history of Europa are exceedingly complex and many large-scale features remain unexplained. True polar wander, involving reorientation of Europa's floating outer ice shell about the tidal axis with Jupiter, has been proposed as a possible explanation for some of the features. This mechanism is possible if the icy shell is latitudinally variable in thickness and decoupled from the rocky interior. It would impose high stress levels on the shell, leading to predictable fracture patterns. No satisfactory match to global-scale features has hitherto been found for polar wander stress patterns. Here we describe broad arcuate troughs and depressions on Europa that do not fit other proposed stress mechanisms in their current position. Using imaging from three spacecraft, we have mapped two global-scale organized concentric antipodal sets of arcuate troughs up to hundreds of kilometres long and 300 m to approximately 1.5 km deep. An excellent match to these features is found with stresses caused by an episode of approximately 80 degrees true polar wander. These depressions also appear to be geographically related to other large-scale bright and dark lineaments, suggesting that many of Europa's tectonic patterns may also be related to true polar wander.

Jupiter's moon Io is known to host active volcanoes. In February and March 2007, the New Horizons spacecraft obtained a global snapshot of Io's volcanism. A 350-kilometer-high volcanic plume was seen to emanate from the Tvashtar volcano (62 degrees N, 122 degrees W), and its motion was observed. The plume's morphology and dynamics support nonballistic models of large Io plumes and also suggest that most visible plume particles condensed within the plume rather than being ejected from the source. In images taken in Jupiter eclipse, nonthermal visible-wavelength emission was seen from individual volcanoes near Io's sub-Jupiter and anti-Jupiter points. Near-infrared emission from the brightest volcanoes indicates minimum magma temperatures in the 1150- to 1335-kelvin range, consistent with basaltic composition.

The New Horizons (NH) spacecraft observed Io's aurora in eclipse on four occasions during spring 2007. NH Alice ultraviolet spectroscopy and concurrent Hubble Space Telescope ultraviolet imaging in eclipse investigate the relative contribution of volcanoes to Io's atmosphere and its interaction with Jupiter's magnetosphere. Auroral brightness and morphology variations after eclipse ingress and egress reveal changes in the relative contribution of sublimation and volcanic sources to the atmosphere. Brightnesses viewed at different geometries are best explained by a dramatic difference between the dayside and nightside atmospheric density. Far-ultraviolet aurora morphology reveals the influence of plumes on Io's electrodynamic interaction with Jupiter's magnetosphere. Comparisons to detailed simulations of Io's aurora indicate that volcanoes supply 1 to 3% of the dayside atmosphere.

Several observations of Jupiter's atmosphere made by instruments on the New Horizons spacecraft have implications for the stability and dynamics of Jupiter's weather layer. Mesoscale waves, first seen by Voyager, have been observed at a spatial resolution of 11 to 45 kilometers. These waves have a 300-kilometer wavelength and phase velocities greater than the local zonal flow by 100 meters per second, much higher than predicted by models. Additionally, infrared spectral measurements over five successive Jupiter rotations at spatial resolutions of 200 to 140 kilometers have shown the development of transient ammonia ice clouds (lifetimes of 40 hours or less) in regions of strong atmospheric upwelling. Both of these phenomena serve as probes of atmospheric dynamics below the visible cloud tops.

When the solar wind hits Jupiter's magnetic field, it creates a long magnetotail trailing behind the planet that channels material out of the Jupiter system. The New Horizons spacecraft traversed the length of the jovian magnetotail to >2500 jovian radii (RJ; 1 RJ identical with 71,400 kilometers), observing a high-temperature, multispecies population of energetic particles. Velocity dispersions, anisotropies, and compositional variation seen in the deep-tail (greater, similar 500 RJ) with a approximately 3-day periodicity are similar to variations seen closer to Jupiter in Galileo data. The signatures suggest plasma streaming away from the planet and injection sites in the near-tail region (approximately 200 to 400 RJ) that could be related to magnetic reconnection events. The tail structure remains coherent at least until it reaches the magnetosheath at 1655 RJ.

The two newly discovered satellites of Pluto (P1 and P2) have masses that are small compared to both Pluto and Charon-that is, between 5 x 10(-4) and 1 x 10(-5) of Pluto's mass, and between 5 x 10(-3) and 1 x 10(-4) of Charon's mass. This discovery, combined with the constraints on the absence of more distant satellites of Pluto, reveal that Pluto and its moons comprise an unusual, highly compact, quadruple system. These facts naturally raise the question of how this puzzling satellite system came to be. Here we show that P1 and P2's proximity to Pluto and Charon, the fact that P1 and P2 are on near-circular orbits in the same plane as Pluto's large satellite Charon, along with their apparent locations in or near high-order mean-motion resonances, all probably result from their being constructed from collisional ejecta that originated from the Pluto-Charon formation event. We also argue that dust-ice rings of variable optical depths form sporadically in the Pluto system, and that rich satellite systems may be found--perhaps frequently--around other large Kuiper belt objects.

Pluto's first known satellite, Charon, was discovered in 1978. It has a diameter (approximately 1,200 km) about half that of Pluto, which makes it larger, relative to its primary, than any other moon in the Solar System. Previous searches for other satellites around Pluto have been unsuccessful, but they were not sensitive to objects less, similar150 km in diameter and there are no fundamental reasons why Pluto should not have more satellites. Here we report the discovery of two additional moons around Pluto, provisionally designated S/2005 P 1 (hereafter P1) and S/2005 P 2 (hereafter P2), which makes Pluto the first Kuiper belt object known to have multiple satellites. These new satellites are much smaller than Charon, with estimates of P1's diameter ranging from 60 km to 165 km, depending on the surface reflectivity; P2 is about 20 per cent smaller than P1. Although definitive orbits cannot be derived, both new satellites appear to be moving in circular orbits in the same orbital plane as Charon, with orbital periods of approximately 38 days (P1) and approximately 25 days (P2).

Large regions of the jovian moon Ganymede have been resurfaced, but the means has been unclear. Suggestions have ranged from volcanic eruptions of liquid water or solid ice to tectonic deformation, but definitive high-resolution morphological evidence has been lacking. Here we report digital elevation models of parts of the surface of Ganymede, derived from stereo pairs combining data from the Voyager and Galileo spacecraft, which reveal bright, smooth terrains that lie at roughly constant elevations 100 to 1,000 metres below the surrounding rougher terrains. These topographic data, together with new images that show fine-scale embayment and burial of older features, indicate that the smooth terrains were formed by flooding of shallow structural troughs by low-viscosity water-ice lavas. The oldest and most deformed areas (the 'reticulate' terrains) in general have the highest relative elevations, whereas units of the most common resurfaced type--the grooved terrain--lie at elevations between those of the smooth and reticulate terrains. Bright terrain, which accounts for some two-thirds of the surface, probably results from a continuum of processes, including crustal rifting, shallow flooding and groove formation. Volcanism plays an integral role in these processes, and is consistent with partial melting of Ganymede's interior.

The Cassini spacecraft completed three close flybys of Saturn's enigmatic moon Enceladus between February and July 2005. On the third and closest flyby, on 14 July 2005, multiple Cassini instruments detected evidence for ongoing endogenic activity in a region centered on Enceladus' south pole. The polar region is the source of a plume of gas and dust, which probably emanates from prominent warm troughs seen on the surface. Cassini's Composite Infrared Spectrometer (CIRS) detected 3 to 7 gigawatts of thermal emission from the south polar troughs at temperatures up to 145 kelvin or higher, making Enceladus only the third known solid planetary body-after Earth and Io-that is sufficiently geologically active for its internal heat to be detected by remote sensing. If the plume is generated by the sublimation of water ice and if the sublimation source is visible to CIRS, then sublimation temperatures of at least 180 kelvin are required.

The nucleus of the Jupiter-family comet 19P/Borrelly was closely observed by the Miniature Integrated Camera and Spectrometer aboard the Deep Space 1 spacecraft on 22 September 2001. The 8-kilometer-long body is highly variegated on a scale of 200 meters, exhibiting large albedo variations (0.01 to 0.03) and complex geologic relationships. Short-wavelength infrared spectra (1.3 to 2.6 micrometers) show a slope toward the red and a hot, dry surface (</=345 kelvin, with no trace of water ice or hydrated minerals), consistent with approximately 10% or less of the surface actively sublimating. Borrelly's coma exhibits two types of dust features: fans and highly collimated jets. At encounter, the near-nucleus coma was dominated by a prominent dust jet that resolved into at least three smaller jets emanating from a broad basin in the middle of the nucleus. Because the major dust jet remained fixed in orientation, it is evidently aligned near the rotation axis of the nucleus.

Analysis of Hubble Space Telescope (HST) images of comet Hale-Bopp (C/1995 O1) suggests that the effective diameter of the nucleus is between 27 to 42 kilometers, which is at least three times larger than that of comet P/Halley. The International Ultraviolet Explorer and HST spectra showed emissions from OH (a tracer of H2O) and CS (a tracer of CS2) starting in April 1996, and from the CO Cameron system (which primarily traces CO2) starting in June 1996. The variation of the H2O production rate with heliocentric distance was consistent with sublimation of an icy body near its subsolar point. The heliocentric variation in the production rates of CS2 and dust was different from that of H2O, which implies that H2O sublimation did not control the CS2 or dust production during these observations.

The Visible, InfraRed, and Thermal Imaging Spectrometer (VIRTIS) on Rosetta obtained hyperspectral images, spectral reflectance maps, and temperature maps of the asteroid 21 Lutetia. No absorption features, of either silicates or hydrated minerals, have been detected across the observed area in the spectral range from 0.4 to 3.5 micrometers. The surface temperature reaches a maximum value of 245 kelvin and correlates well with topographic features. The thermal inertia is in the range from 20 to 30 joules meter(-2) kelvin(-1) second(-0.5), comparable to a lunarlike powdery regolith. Spectral signatures of surface alteration, resulting from space weathering, seem to be missing. Lutetia is likely a remnant of the primordial planetesimal population, unaltered by differentiation processes and composed of chondritic materials of enstatitic or carbonaceous origin, dominated by iron-poor minerals that have not suffered aqueous alteration.

We report, for the f irst time to our knowledge, comparisons of light-scattering computations for large, randomly oriented, moderately absorbing spheroids based on the geometric-optics approximation and the exact T-matrix method. We show that in most cases the geometric-optics approximation is (much) more accurate for spheroids than for surface-equivalent spheres and can be used in phase function computations (but not in polarization computations) for nonspherical particles with size parameters as small as 60. Differences in the single-scattering albedo between geometric-optics and T-matrix results are surprisingly small, even for small size parameters.

The propagation of high-peak-power (>10-kW) sub-100-fs pulses near the zero-dispersion wavelength of an optical fiber was studied experimentally. Four-photon mixing and stimulated Raman scattering were observed for fiber lengths greater than 2 m. With pulses as short as 25 fs, four-photon mixing dominates, resulting in efficient conversion of the input pulse spectrum into two coherent spectral bands. This can be used to extend the useful wavelength range of femtosecond lasers in the infrared.

Exposure of germanosilicate fibers to cw UV light at 351.1 nm from an argon-ion laser is shown to have dramatic effects on the seeded preparation of the material for second-harmonic generation. We show that 100 microW of 351.1-nm radiation for periods as short as 20 s leads to large, permanent enhancements of the second-harmonic conversion efficiency. The UV exposure provides an increase of 7 orders of magnitude in final conversion efficiency in one regime of IR preparation intensity and allows preparation with cw IR and second-harmonic wavelengths. In addition, the 351.1-nm wavelength was shown to erase the chi((2)) grating much more efficiently than did 514.5-nm radiation.

We experimentally investigate the wavelength effect on high-order harmonic generation (HHG) in CH(4) molecules and Xe atoms driven by a tunable infrared parametric source, and observe that the molecular HHG around the vibrational resonance is more sensitive to the driver wavelength than HHG from an atomic gas with comparable ionization potential. The results can be attributed to the light nuclear motion induced by the driving laser field, and it becomes possible to control the proton vibration in the molecular HHG by tuning the infrared wavelength of the driving laser.

The enhanced optical absorptance in metals was recently demonstrated using femtosecond laser-induced surface structuring. This structuring was obtained by simply focusing the light to the sample surface. Here we demonstrate more efficient absorptance enhancement using interferometric ablation. This interferometric ablation technique produces deeper surface structures and, consequently, higher absorption than structures obtained by just focusing the light to the surface. We also show the measured reflectance spectra over visible region for unaltered and structured stainless steel and copper samples.

A scanning polarized lidar was used to detect flying honey bees trained to locate buried land mines through odor detection. A lidar map of bee density shows good correlation with maps of chemical plume strength and bee density determined by visual and video counts. The co-polarized lidar backscatter signal was found to be more effective than the crosspolarized signal for detecting honey bees in flight. Laboratory measurements show that the depolarization ratio of scattered light is near zero for bee wings and up to 30% for bee bodies.

Reactions of laser-ablated Pt atoms with CH 4 during condensation in excess argon form CH 3-PtH through oxidative C-H insertion show and that the late transition-metal atom Pt is an effective methane activation reagent, in agreement with gas phase investigations. Six observed infrared absorptions correlate with the six strongest calculated harmonic frequencies. The computed C-Pt bond length is slightly shorter than those of Pt complexes with large ligands. In addition, the strongest absorption of the CH 2PtH 2 methylidene is detected.

We demonstrate that solarization occurs in glass substrates during thin-film deposition and that it induces high absorption near the surface of the substrate. Solarization has been observed especially in ion-plating deposition. We show that the solarization of the substrate is caused by electromagnetic radiation emitted from the material to be evaporated. The radiation is due to the energy losses of the heating beam of electrons (bremsstrahlung radiation). Multicomponent glasses such as BK7 are much more sensitive to solarization than fused-silica substrates. The photoinduced high absorption can be partially reversed by thermal annealing.

Jupiter's moon Io is known to host active volcanoes. In February and March 2007, the New Horizons spacecraft obtained a global snapshot of Io's volcanism. A 350-kilometer-high volcanic plume was seen to emanate from the Tvashtar volcano (62 degrees N, 122 degrees W), and its motion was observed. The plume's morphology and dynamics support nonballistic models of large Io plumes and also suggest that most visible plume particles condensed within the plume rather than being ejected from the source. In images taken in Jupiter eclipse, nonthermal visible-wavelength emission was seen from individual volcanoes near Io's sub-Jupiter and anti-Jupiter points. Near-infrared emission from the brightest volcanoes indicates minimum magma temperatures in the 1150- to 1335-kelvin range, consistent with basaltic composition.