Modelling of Magnetosphere-Ionosphere Coupling in the Jovian System

Auroral emissions are generated through the acceleration of current carriers along magnetic field lines, with particles precipitating into the atmosphere of a planet. The distribution of plasma within the planetary magnetosphere determines the potential structure along the field lines and is therefore influenced by the characteristics of magnetospheric and ionospheric particle sources. This in turn, influences the generated aurora. At the Jovian system, the particle dynamics are complex. Heavy ions are confined to the centrifugal equator of the planet due to strong centrifugal forces; magnetospheric electrons are unable to reach high magnetic latitudes due to the magnetic mirror effect; ionospheric plasma cannot reach high latitudes due to large gravitational forces. Due to these restrictions, a field-aligned accelerating potential will be generated, occurring close to the minimum of the sum of the centrifugal and gravitational potentials. This will result in precipitating electrons and ions being accelerated, resulting in auroral emission in the UV and X-ray regimes, respectively. To gain understanding of the dynamics of the Jovian magnetosphere and auroral generation, work is underway on adapting an existing terrestrial model. This numeric code is a parallelised, kinetic Vlasov solver, which models the evolution of plasma species along magnetic field lines, and thus determining the structure of auroral acceleration regions at Earth. Through the use of a non-uniform spatial grid, the model allows fine resolution in specific regions of interest (e.g. at the ionosphere). Efforts are currently underway to introduce centrifugal forces to the model, allowing it to accurately model the rapidly rotating Jovian system. In addition, species will have the option of be treated as a fluid, improving computational time. The refined model will quantify the energy transferred to Jupiter’s atmosphere through auroral precipitation, thus allowing comparison and interpretation of insitu measurements made by the Juno spacecraft

1-D Hybrid Kinetic/Fluid Modelling of the Jovian Magnetosphere

Based on early measurements from the Juno spacecraft, magnetosphere-ionosphere-thermosphere (MIT) coupling studies of the Jovian system are thought to have under-estimated the densities of plasma species in the high-latitude regions of the magnetosphere. As the main auroral oval of Jupiter is driven by particles precipitating into the planetary atmosphere in these regions, characterising the density and potential structure along high-latitude magnetic field lines is of particular interest. To that end, a 1-D spatial, 2-D velocity hybrid kinetic/fluid model is under development. This model will allow the middle magnetosphere regions (~20-50 RJ) responsible for the main oval to be investigated numerically. Previous 1-D kinetic models of the Jovian system have been constrained to the Io flux tube. Through the use of code parallelisation, non-uniform spatial mesh and fluid treatment of species, the computational challenge of modelling of the Jovian middle magnetosphere can be reduced. The model allows density profiles, potential structures, current flow and precipitating particle fluxes to be found. Comparison of these outputs to data from Juno will help to validate the model, along with providing refinements to MIT theory

Warm protons at comet 67P/Churyumov–Gerasimenko – implications for the infant bow shock

The plasma around comet 67P/Churyumov–Gerasimenko showed remarkable variability throughout the entire Rosetta mission. Plasma boundaries such as the diamagnetic cavity, solar wind ion cavity and infant bow shock separate regions with distinct plasma parameters from each other. Here, we focus on a particular feature in the plasma: warm, slow solar wind protons. We investigate this particular proton population further by focusing on the proton behaviour and surveying all of the Rosetta comet phase data. We find over 300 events where Rosetta transited from a region with fast, cold protons into a region with warm, slow protons. We investigate the properties of the plasma and magnetic field at this boundary and the location where it can be found. We find that the protons are preferentially detected at intermediate gas production rates with a slight trend towards larger cometocentric distances for higher gas production rates. The events can mostly be found in the positive convective electric field hemisphere. These results agree well with simulations of the infant bow shock (IBS), an asymmetric structure in the plasma environment previously detected on only 2 d during the comet phase. The properties of the plasma on both sides of this structure are harder to constrain, but there is a trend towards higher electron flux, lower magnetic field, higher magnetic field power spectral density and higher density in the region that contains the warm protons. This is in partial agreement with the previous IBS definitions; however, it also indicates that the plasma and this structure are highly non-stationary. For future research, Comet Interceptor, with its multi-point measurements, can help to disentangle the spatial and temporal effects and give more clarity on the influence of changing upstream conditions on the movement of boundaries in this unusual environment

Halogens as tracers of protosolar nebula material in comet 67P/Churyumov–Gerasimenko

We report the first in situ detection of halogens in a cometary coma, that of 67P/ChuryumovGerasimenko. Neutral gas mass spectra collected by the European Space Agency’s Rosetta spacecraft during four periods of interest from the first comet encounter up to perihelion indicate that the main halogen-bearing compounds are HF, HCl and HBr. The bulk elemental abundances relative to oxygen are ~8.9 × 10⁻⁵ for F/O, ~1.2 × 10⁻⁴ for Cl/O and ~2.5 × 10⁻⁶ for Br/O, for the volatile fraction of the comet. The cometary isotopic ratios for ³⁷Cl/³⁵Cl and ⁸¹Br/⁷⁹Br match the Solar system values within the error margins. The observations point to an origin of the hydrogen halides in molecular cloud chemistry, with frozen hydrogen halides on dust grains, and a subsequent incorporation into comets as the cloud condensed and the Solar system formed

The Comet Interceptor Mission

Here we describe the novel, multi-point Comet Interceptor mission. It is dedicated to the exploration of a little-processed long-period comet, possibly entering the inner Solar System for the first time, or to encounter an interstellar object originating at another star. The objectives of the mission are to address the following questions: What are the surface composition, shape, morphology, and structure of the target object? What is the composition of the gas and dust in the coma, its connection to the nucleus, and the nature of its interaction with the solar wind? The mission was proposed to the European Space Agency in 2018, and formally adopted by the agency in June 2022, for launch in 2029 together with the Ariel mission. Comet Interceptor will take advantage of the opportunity presented by ESA's F-Class call for fast, flexible, low-cost missions to which it was proposed. The call required a launch to a halo orbit around the Sun-Earth L2 point. The mission can take advantage of this placement to wait for the discovery of a suitable comet reachable with its minimum ΔV capability of 600 ms-1. Comet Interceptor will be unique in encountering and studying, at a nominal closest approach distance of 1000 km, a comet that represents a near-pristine sample of material from the formation of the Solar System. It will also add a capability that no previous cometary mission has had, which is to deploy two sub-probes - B1, provided by the Japanese space agency, JAXA, and B2 - that will follow different trajectories through the coma. While the main probe passes at a nominal 1000 km distance, probes B1 and B2 will follow different chords through the coma at distances of 850 km and 400 km, respectively. The result will be unique, simultaneous, spatially resolved information of the 3-dimensional properties of the target comet and its interaction with the space environment. We present the mission's science background leading to these objectives, as well as an overview of the scientific instruments, mission design, and schedule

The Comet Interceptor Mission

Here we describe the novel, multi-point Comet Interceptor mission. It is dedicated to the exploration of a little-processed long-period comet, possibly entering the inner Solar System for the first time, or to encounter an interstellar object originating at another star. The objectives of the mission are to address the following questions: What are the surface composition, shape, morphology, and structure of the target object? What is the composition of the gas and dust in the coma, its connection to the nucleus, and the nature of its interaction with the solar wind? The mission was proposed to the European Space Agency in 2018, and formally adopted by the agency in June 2022, for launch in 2029 together with the Ariel mission. Comet Interceptor will take advantage of the opportunity presented by ESA’s F-Class call for fast, flexible, low-cost missions to which it was proposed. The call required a launch to a halo orbit around the Sun-Earth L2 point. The mission can take advantage of this placement to wait for the discovery of a suitable comet reachable with its minimum ΔV capability of 600 ms−1. Comet Interceptor will be unique in encountering and studying, at a nominal closest approach distance of 1000 km, a comet that represents a near-pristine sample of material from the formation of the Solar System. It will also add a capability that no previous cometary mission has had, which is to deploy two sub-probes – B1, provided by the Japanese space agency, JAXA, and B2 – that will follow different trajectories through the coma. While the main probe passes at a nominal 1000 km distance, probes B1 and B2 will follow different chords through the coma at distances of 850 km and 400 km, respectively. The result will be unique, simultaneous, spatially resolved information of the 3-dimensional properties of the target comet and its interaction with the space environment. We present the mission’s science background leading to these objectives, as well as an overview of the scientific instruments, mission design, and schedule

Interacting Eigenmodes of a Plasma Diode with a Density Gradient

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