| 1. |
- Jones, Geraint H., et al.
(författare)
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The Comet Interceptor Mission
- 2024
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Ingår i: Space Science Reviews. - : Springer Nature. - 0038-6308 .- 1572-9672. ; 220:1
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Tidskriftsartikel (refereegranskat)abstract
- 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 Δ V 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.
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| 2. |
- Simon Wedlund, Cyril, et al.
(författare)
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A Fast Bow Shock Location Predictor-Estimator From 2D and 3D Analytical Models : Application to Mars and the MAVEN Mission
- 2022
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Ingår i: Journal of Geophysical Research - Space Physics. - : John Wiley & Sons. - 2169-9380 .- 2169-9402. ; 127:1
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Tidskriftsartikel (refereegranskat)abstract
- We present fast algorithms to automatically estimate the statistical position of the bow shock from spacecraft data, using existing analytical two-dimensional (2D) and three-dimensional (3D) models of the shock surface. We derive expressions of the standoff distances in 2D and 3D and of the normal to the bow shock at any given point on it. Two simple bow shock detection algorithms are constructed, one solely based on a geometrical predictor from existing models, the other using this predicted position to further refine it with the help of magnetometer data, an instrument flown on many planetary missions. Both empirical techniques are applicable to any planetary environment with a defined shock structure. Applied to the Martian environment and the NASA/MAVEN mission, the predicted shock position is on average within 0.15 planetary radius Rp of the bow shock crossing. Using the predictor-corrector algorithm, this estimate is further refined to within a few minutes of the true crossing (≈0.05Rp). Between 2014 and 2021, we detect 14,929 clear bow shock crossings, predominantly quasi-perpendicular. Thanks to 2D conic and 3D quadratic fits, we investigate the variability of the shock surface with respect to Mars Years (MY), solar longitude (Ls), and solar EUV flux levels. Although asymmetry in Y and Z Mars Solar Orbital coordinates is on average small, we show that for MY32 and MY35, Ls = [135°−225°] and high solar flux, it can become particularly noticeable, and is superimposed to the usual North-South asymmetry due in part to the presence of crustal magnetic fields.
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| 3. |
- Dieval, Catherine
(författare)
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Solar wind ions inside the induced magnetosphere of Mars
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The subject of the thesis is analysis and modeling of the entry, transport, and atmospheric precipitation of solar wind ions, H+ and He2+, into the induced magnetosphere of Mars. The solar wind is a flow of charged particles emitted by the Sun. The solar wind carries with it a magnetic field, the interplanetary magnetic field (IMF). The IMF piles up on the dayside of the non-magnetized Mars and is then convected towards the nightside. The solar wind ions can normally not cross the magnetic barrier, formed by the pile up IMF. However, in situ observations by the Mars Express spacecraft reveal that downward moving solar wind H+ and He2+ are sometimes present in the Martian ionosphere, below the magnetic barrier. The gyroradii of shocked solar wind ions may be comparable to the size of the dayside Martian magnetic barrier and for certain circumstances, these ions can gyrate through. Observations by Mars Express are used to analyze H+ and He2+ penetrating through the magnetic barrier and precipitating into the Martian ionosphere, identified by the presence of ionospheric photo-electrons. A case study shows evidence of narrower energy distributions for H+ (with energy ≥ solar wind energy), as the spacecraft moves down in altitude. From this, the study concludes that the magnetic barrier prevents the lower energy H+, from reaching low altitudes. The thesis also describes a statistical study of precipitating H+ fluxes, which indicate that H+ precipitation is rare (detected during 3% of the dayside observation time only) and carries on average 0.2% of the upstream solar wind particle flux. In another statistical study, the thesis shows that the precipitation of H+ and He2+ decreases even further when Mars encounters solar wind pressure pulses. A possible explanation is that the enhanced mass loading of the magnetic field flux tubes by planetary heavy ions, while the tubes drag through the ionosphere at lower altitudes, slows down their velocity and allows more magnetic flux to pile up. The magnetic barrier becomes a more effective obstacle to the solar wind ion precipitation. Furthermore, the thesis describes a model of H+ precipitation onto the Martian upper atmosphere using a hybrid code of the Mars solar wind interaction. The spatial patterns of the precipitation depend on the H+ energy, on the H+ origin (solar wind or generated from the hydrogen corona) and on the altitude. Some features of the observed H+ distributions are reproduced by simulations, while others are not, indicating a more complex physics than in the model. The thesis also describes amodel study of transport of H+, fast H atoms and He2+ through the atmosphere using a Direct Simulation Monte Carlo model. This study demonstrates the crucial role of the magnetic field in determining the energy deposition of the solar wind ions in the topside atmosphere. For instance, a horizontal magnetic field with strength of 50 nT backscattered almost all H+, thus preventing these particles to deposit their energy at lower altitudes. The conclusion of the thesis work is that although some solar wind ions do precipitate, the magnetic barrier effectively protects the onospherefrom precipitating solar wind ions.
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| 4. |
- Lalti, Ahmad
(författare)
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Electrostatic turbulence and electron heating in collisionless shocks
- 2024
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- When the supersonic solar wind interacts with Earth’s magnetosphere it forms a shock wave. However, due to the low densities in space, inter-particle collisions play an insignificant role in its dynamics. Earth's bow shock is an example of a collisionless shock, ubiquitous throughout the universe. Their dynamics are complex and their physics remains an active field of research. In this thesis, we use high-resolution measurements from NASA's Magnetospheric Multiscale (MMS) spacecraft to study the plasma wave activity across Earth’s bow shock and its effects on electron heating. In Paper I we train a convolutional neural network (CNN) to identify the different plasma regions that MMS crosses. In Paper II we use the results of this CNN to compile a database of time intervals in which MMS crosses Earth’s bow shock, which we use to find suitable events to tackle the science questions of interest. In Paper III we use multispacecraft methods to properly characterize obliquely propagating whistler waves running upstream of the shock. By analyzing the ion and electron distribution functions we find that their likely source is the instability between the incoming electrons and reflected ions. Shifting our focus to Debye scale electrostatic waves, in Paper IV we develop a method to measure their 3D wave vector based on single-spacecraft interferometry. We are in the process of using this method to study the evolution of Debye scale electrostatic waves across quasi-perpendicular shocks (see Chapter 7). Finally, in Paper V we investigate the electron heating mechanism across quasi-perpendicular shocks. We find the heating mechanism to depend on the Alfvénic Mach number in the deHoffman-Teller frame . We also find that at high the heating mechanism is consistent with the stochastic shock drift acceleration mechanism.
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| 5. |
- Sánchez-Cano, Beatriz, et al.
(författare)
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Mars’ plasma system. Scientific potential of coordinated multipoint missions : "The next generation"
- 2022
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Ingår i: Experimental astronomy. - : Springer. - 0922-6435 .- 1572-9508. ; 54, s. 641-676
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Tidskriftsartikel (refereegranskat)abstract
- The objective of this White Paper, submitted to ESA’s Voyage 2050 call, is to get a more holistic knowledge of the dynamics of the Martian plasma system, from its surface up to the undisturbed solar wind outside of the induced magnetosphere. This can only be achieved with coordinated multi-point observations with high temporal resolution as they have the scientific potential to track the whole dynamics of the system (from small to large scales), and they constitute the next generation of the exploration of Mars analogous to what happened at Earth a few decades ago. This White Paper discusses the key science questions that are still open at Mars and how they could be addressed with coordinated multipoint missions. The main science questions are: (i) How does solar wind driving impact the dynamics of the magnetosphere and ionosphere? (ii) What is the structure and nature of the tail of Mars’ magnetosphere at all scales? (iii) How does the lower atmosphere couple to the upper atmosphere? (iv) Why should we have a permanent in-situ Space Weather monitor at Mars? Each science question is devoted to a specific plasma region, and includes several specific scientific objectives to study in the coming decades. In addition, two mission concepts are also proposed based on coordinated multi-point science from a constellation of orbiting and ground-based platforms, which focus on understanding and solving the current science gaps.
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