Magnetic reconnection near the planet as a possible driver of Jupiter's mysterious polar auroras

Auroral emissions have been extensively observed at the Earth, Jupiter, and Saturn. These planets all have appreciable atmospheres and strong magnetic fields, and their auroras predominantly originate from a region encircling each magnetic pole. However, Jupiter’s auroras poleward of these “main” emissions are brighter and more dynamic, and the drivers responsible for much of these mysterious polar auroras have eluded identification to date. We propose that part of the solution may stem from Jupiter’s stronger magnetic field. We model large-scale Alfvénic perturbations propagating through the polar magnetosphere towards Jupiter, showing that the resulting <0.1° deflections of the magnetic field closest to the planet could trigger magnetic reconnection as near as ∼0.2 Jupiter radii above the cloud tops. At Earth and Saturn this physics should be negligible, but reconnection electric field strengths above Jupiter’s poles can approach ∼1 V m-1, typical of the solar corona. We suggest this near-planet reconnection could generate beams of high-energy electrons capable of explaining some of Jupiter’s polar auroras

The mechanical and electrical properties of direct-spun carbon nanotube mats

The mechanical and electrical properties of a direct-spun carbon nanotube mat are measured. The mat comprises an interlinked random network of nanotube bundles, with approximately 40 nanotubes in a bundle. A small degree of in-plane anisotropy is observed. The bundles occasionally branch, and the mesh topology resembles a 2D lattice of nodal connectivity slightly below 4. The macroscopic in-plane tensile response is elasto-plastic in nature, with significant orientation hardening. In-situ microscopy reveals that the nanotube bundles do not slide past each other at their junctions under macroscopic stain. A micromechanical model is developed to relate the macroscopic modulus and flow strength to the longitudinal shear response of the nanotube bundles. The mechanical and electrical properties of the mat are compared with those of other nanotube arrangements over a wide range of density

The H₃⁺ ionosphere of Uranus: decades-long cooling and local-time morphology

The upper atmosphere of Uranus has been observed to be slowly cooling between 1993 and 2011. New analysis of near-infrared observations of emission from H₃⁺ obtained between 2012 and 2018 reveals that this cooling trend has continued, showing that the upper atmosphere has cooled for 27 years, longer than the length of a nominal season of 21 years. The new observations have offered greater spatial resolution and higher sensitivity than previous ones, enabling the characterization of the H₃⁺ intensity as a function of local time. These profiles peak between 13 and 15 h local time, later than models suggest. The NASA Infrared Telescope Facility iSHELL instrument also provides the detection of a bright H₃⁺ signal on 16 October 2016, rotating into view from the dawn sector. This feature is consistent with an auroral signal, but is the only of its kind present in this comprehensive dataset

Anthropogenic perturbation of the carbon fluxes from land to ocean

A substantial amount of the atmospheric carbon taken up on land through photosynthesis and chemical weathering is transported laterally along the aquatic continuum from upland terrestrial ecosystems to the ocean. So far, global carbon budget estimates have implicitly assumed that the transformation and lateral transport of carbon along this aquatic continuum has remained unchanged since pre-industrial times. A synthesis of published work reveals the magnitude of present-day lateral carbon fluxes from land to ocean, and the extent to which human activities have altered these fluxes. We show that anthropogenic perturbation may have increased the flux of carbon to inland waters by as much as 1.0 Pg C yr-1 since pre-industrial times, mainly owing to enhanced carbon export from soils. Most of this additional carbon input to upstream rivers is either emitted back to the atmosphere as carbon dioxide (~0.4 Pg C yr-1) or sequestered in sediments (~0.5 Pg C yr-1) along the continuum of freshwater bodies, estuaries and coastal waters, leaving only a perturbation carbon input of ~0.1 Pg C yr-1 to the open ocean. According to our analysis, terrestrial ecosystems store ~0.9 Pg C yr-1 at present, which is in agreement with results from forest inventories but significantly differs from the figure of 1.5 Pg C yr-1 previously estimated when ignoring changes in lateral carbon fluxes. We suggest that carbon fluxes along the land–ocean aquatic continuum need to be included in global carbon dioxide budgets.Peer reviewe

The mechanical and electrical properties of direct-spun carbon nanotube mats

The mechanical and electrical properties of a direct-spun carbon nanotube mat are measured. The mat comprises an interlinked random network of nanotube bundles, with approximately 40 nanotubes in a bundle. A small degree of in-plane anisotropy is observed. The bundles occasionally branch, and the mesh topology resembles a 2D lattice of nodal connectivity slightly below 4. The macroscopic in-plane tensile response is elasto-plastic in nature, with significant orientation hardening. In-situ microscopy reveals that the nanotube bundles do not slide past each other at their junctions under macroscopic strain. A micromechanical model is developed to relate the macroscopic modulus and flow strength to the longitudinal shear response of the nanotube bundles. The mechanical and electrical properties of the mat are compared with those of other nanotube arrangements over a wide range of density

Magnetic reconnection near the planet as a possible driver of Jupiter’s mysterious polar auroras

Auroral emissions have been extensively observed at the Earth, Jupiter, and Saturn. These planets all have appreciable atmospheres and strong magnetic fields, and their auroras predominantly originate from a region encircling each magnetic pole. However, Jupiter’s auroras poleward of these “main” emissions are brighter and more dynamic, and the drivers responsible for much of these mysterious polar auroras have eluded identification to date. We propose that part of the solution may stem from Jupiter’s stronger magnetic field. We model large-scale Alfvénic perturbations propagating through the polar magnetosphere toward Jupiter, showing that the resulting Plain Language SummaryWhen energetic particles from space hit a planet’s upper atmosphere the resulting chemistry can produce light, leading to spectacular “auroras.” Jupiter is the largest planet in the Solar System, with the strongest magnetic field generated in its interior, and with the brightest auroras. We understand why Jupiter’s auroras are so bright to a large extent, but a long-standing mystery is what causes the swirling auroras around Jupiter’s poles, which we do not see at other planets. We present a new idea that might lead to a solution to this problem. We show that under certain conditions in space just above Jupiter’s polar atmosphere some of the energy stored in the planet’s magnetic field can be released, possibly accelerating particles and producing auroras below. If this idea is supported by future research it would imply that Jupiter’s bright polar auroras are due to the planet’s very strong magnetic field, with implications for similarly strongly magnetized planets in orbit around distant stars.</div

Observations of the chemical and thermal response of ‘ring rain’ on Saturn’s ionosphere

In this study we performed a new analysis of ground-based observations that were taken on 17 April 2011 using the 10-metre Keck telescope on Mauna Kea, Hawaii. Emissions from H+3, a major ion in Saturn’s ionosphere, were previously analyzed from these observations, indicating that peaks in emission at specific latitudes were consistent with an influx of charged water products from the rings known as ‘ring rain’. Subsequent modeling showed that these peaks in emission are best explained by an increase in H+3 density, rather than in column-averaged H+3temperatures, as a local reduction in electron density (due to charge exchange with water) lengthens the lifetime of H+ 3. However, what has been missing until now is a direct derivation of the H +3 parameters temperature, density and radiative cooling rates, which are required to confirm and expand on existing models and theory. Here we present measurements of these H+3 parameters for the first time in the non-auroral regions of Saturn, using two H+3 lines, Q(1,0−) and R(2,2). We confirm that H + 3 density is enhanced near the expected ‘ring rain’ planetocentric latitudes near 45◦N and 39◦S. A low H+3 density near 31◦S, an expected prodigious source of water, may indicate that the rings are ‘overflowing’ material into the planet such that H+ 3 destruction by charge-exchange with incoming neutrals outweighs its lengthened lifetime due to the aforementioned reduction in electron density. Derived H+ 3 temperatures were low while the density was high at 39◦S, potentially indicating that the ionosphere is most affected by ring rain in the deep ionosphere. Saturn’s moon Enceladus, a known water source, is connected with a dense region of H+ 3 centered on 62◦S, perhaps indicating that charged water from Enceladus is draining into Saturn’s southern mid-latitudes. We estimated the water product influx using previous modeling results, finding that 432 - 2870 kg s−1 of water delivered to Saturn’s mid-latitudes is sufficient to explain the observed H+ 3 densities. When considering this mechanism alone, Saturn will lose its rings in 292+818 −124 million years