Jupiter's main ring shows vertical corrugations reminiscent of those recently detected in the rings of Saturn. The Galileo spacecraft imaged a pair of superimposed ripple patterns in 1996 and again in 2000. These patterns behave as two independent spirals, each winding up at a rate defined by Jupiter's gravity field. The dominant pattern originated between July and October 1994, when the entire ring was tilted by about 2 kilometers. We associate this with the Shoemaker-Levy 9 impacts of July 1994. New Horizons images still show this pattern 13 years later and suggest that subsequent events may also have tilted the ring. Impacts by comets or their dust streams are regular occurrences in planetary rings, altering them in ways that remain detectable decades later.

We review our understanding of Saturn's rings after nearly 6 years of observations by the Cassini spacecraft. Saturn's rings are composed mostly of water ice but also contain an undetermined reddish contaminant. The rings exhibit a range of structure across many spatial scales; some of this involves the interplay of the fluid nature and the self-gravity of innumerable orbiting centimeter- to meter-sized particles, and the effects of several peripheral and embedded moonlets, but much remains unexplained. A few aspects of ring structure change on time scales as short as days. It remains unclear whether the vigorous evolutionary processes to which the rings are subject imply a much younger age than that of the solar system. Processes on view at Saturn have parallels in circumstellar disks.

Polyamines are essential metabolites in eukaryotes participating in a variety of proliferative processes, and in trypanosomatid protozoa play an additional role in the synthesis of the critical thiol trypanothione. Whereas the polyamine biosynthesis arising from l-ornithine has been well studied in protozoa, the metabolic origin(s) of l-ornithine have received less attention. Arginase (EC 3.5.3.1) catalyzes the enzymatic hydrolysis of l-arginine to l-ornithine and urea, and we tested the role of arginase in polyamine synthesis by the generation of an arg(?) knockout in Leishmania major by double targeted gene replacement. This mutant lacked arginase activity and required the nutritional provision of polyamines or l-ornithine for growth. A complemented line (arg(?)/+ARG) expressing arginase from a multi-copy expression vector showed 30-fold elevation of arginase activity, similar polyamine and ornithine levels as the wild-type, and resistance to the inhibitors ?-difluoromethylornithine (DFMO) and N(?)-hydroxy-l-arginine (NOHA). This established that arginase is the major route of polyamine synthesis in promastigotes cultured in vitro. The arg(?) parasites retained the ability to differentiate normally to the infective metacyclic stage, and were able to induce progressive disease following inoculation into susceptible BALB/c mice, albeit less efficiently than WT parasites. These data suggest that the infective amastigote form of Leishmania, which normally resides within an acidified parasitophorous vacuole, can survive in vivo through salvage of host polyamines and/or other molecules, aided by the tendency of acidic compartments to concentrate basic metabolites. This may thus contribute to the relative resistance of Leishmania to ornithine decarboxylase (ODC) inhibitors. The availability of infective, viable, arginase-deficient parasites should prove useful in dissecting the role of l-arginine metabolism in both pro- and anti-parasitic responses involving host nitric oxide synthase, which requires l-arginine to generate NO.

Surface phosophoglycans such as lipophosphoglycan (LPG) or proteophosphoglycan (PPG) and glycosylinositol phospholipids (GIPLs) modulate essential interactions between Leishmania and mammalian macrophages. Phosphoglycan synthesis depends on the Golgi GDP-mannose transporter encoded by LPG2. LPG2-null (lpg2(-)) Leishmania major cannot establish macrophage infections or induce acute pathology, whereas lpg2(-)Leishmania mexicana retain virulence. lpg2(-)Leishmaniadonovani has been reported to survive poorly in cultured macrophages but in vivo survival has not been explored. Herein we discovered that, similar to lpg2(-)L. major, lpg2(-)L. donovani promastigotes exhibited diminished virulence in mice, but persisted at consistently low levels. lpg2(-)L. donovani promastigotes could not establish infection in macrophages and could not transiently inhibit phagolysosomal fusion. Furthermore, lpg2(-) promastigotes of L. major, L. donovani and L. mexicana were highly susceptible to complement-mediated lysis. We conclude that phosphoglycan assembly and expression mediated by L. donovani LPG2 are important for promastigote and amastigote virulence, unlike L. mexicana but similar to L. major.

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 dusty jovian ring system must be replenished continuously from embedded source bodies. The New Horizons spacecraft has performed a comprehensive search for kilometer-sized moons within the system, which might have revealed the larger members of this population. No new moons were found, however, indicating a sharp cutoff in the population of jovian bodies smaller than 8-kilometer-radius Adrastea. However, the search revealed two families of clumps in the main ring: one close pair and one cluster of three to five. All orbit within a brighter ringlet just interior to Adrastea. Their properties are very different from those of the few other clumpy rings known; the origin and nonrandom distribution of these features remain unexplained, but resonant confinement by Metis may play a role.

Careful reprocessing of the Voyager images reveals that the Uranìan lambda ring has marked longitudinal variations in brightness comparable in magnitude to those in Saturn's F ring and Neptune's Adams ring. The ring's variations show a dominant five-cycle (72-degree) periodicity, although additional structure down to scales of about 0.5 degree is also present. The ring's shape is defined by a small overall eccentricity plus a six-cycle (60-degree) sinusoidal variation of radial amplitude around 4 kilometers. Both of these properties can be explained by the resonant perturbations of a moon at a semimajor axis of 56,479 kilometers, but no known moon orbits at this location. Unfortunately, the mass required suggests that such a body should have been imaged by Voyager.

Voyager 2 images of Neptune reveal a windy planet characterized by bright clouds of methane ice suspended in an exceptionally clear atmosphere above a lower deck of hydrogen sulfide or ammonia ices. Neptune's atmosphere is dominated by a large anticyclonic storm system that has been named the Great Dark Spot (GDS). About the same size as Earth in extent, the GDS bears both many similarities and some differences to the Great Red Spot of Jupiter. Neptune's zonal wind profile is remarkably similar to that of Uranus. Neptune has three major rings at radii of 42,000, 53,000, and 63,000 kilometers. The outer ring contains three higher density arc-like segments that were apparently responsible for most of the ground-based occultation events observed during the current decade. Like the rings of Uranus, the Neptune rings are composed of very dark material; unlike that of Uranus, the Neptune system is very dusty. Six new regular satellites were found, with dark surfaces and radii ranging from 200 to 25 kilometers. All lie inside the orbit of Triton and the inner four are located within the ring system. Triton is seen to be a differentiated body, with a radius of 1350 kilometers and a density of 2.1 grams per cubic centimeter; it exhibits clear evidence of early episodes of surface melting. A now rigid crust of what is probably water ice is overlain with a brilliant coating of nitrogen frost, slightly darkened and reddened with organic polymer material. Streaks of organic polymer suggest seasonal winds strong enough to move particles of micrometer size or larger, once they become airborne. At least two active plumes were seen, carrying dark material 8 kilometers above the surface before being transported downstream by high level winds. The plumes may be driven by solar heating and the subsequent violent vaporization of subsurface nitrogen.

The rings of Uranus are oriented edge-on to Earth in 2007 for the first time since their 1977 discovery. This provides a rare opportunity to observe their dark (unlit) side, where dense rings darken to near invisibility, but faint rings become much brighter. We present a ground-based infrared image of the unlit side of the rings that shows that the system has changed dramatically since previous views. A broad cloud of faint material permeates the system, but is not correlated with the well-known narrow rings or with the embedded dust belts imaged by Voyager. Although some differences can be explained by the unusual viewing angle, we conclude that the dust distribution within the system has changed significantly since the 1986 Voyager spacecraft encounter and occurs on much larger scales than has been seen in other planetary systems.