Reduced proton and alpha particle precipitation at Mars during solar wind pressure pulses:Mars Express results

We performed a statistical study of downward moving protons and alpha particles of ~keV energy (assumed to be of solar wind origin) inside the Martian induced magnetosphere from July 2006 to July 2010. Ion and electron data are from the Analyzer of Space Plasma and Energetic Atoms (ASPERA-3) package on board Mars Express. We investigated the solar wind ion entry into the ionosphere, excluding intervals of low-altitude magnetosheath encounters. The study compares periods of quiet solar wind conditions and periods of solar wind pressure pulses, including interplanetary coronal mass ejections and corotating interaction regions. The solar wind ion precipitation appears localized and/or intermittent, consistent with previous measurements. Precipitation events are less frequent, and the precipitating fluxes do not increase during pressure pulse encounters. During pressure pulses, the occurrence frequency of observed proton precipitation events is reduced by a factor of ~3, and for He^2+ events the occurrence frequency is reduced by a factor of ~2. One explanation is that during pressure pulse periods, the mass loading of the solar wind plasma increases due to a deeper penetration of the interplanetary magnetic flux tubes into the ionosphere. The associated decrease of the solar wind speed thus increases the pileup of the interplanetary magnetic field on the dayside of the planet. The magnetic barrier becomes thicker in terms of solar wind ion gyroradii, causing the observed reduction of H^+/He^2+ precipitations

A Potential Aid in the Target Selection for the Comet Interceptor Mission

The upcoming Comet Interceptor mission involves a parking phase around the Sun-Earth L2 point before transferring to intercept the orbit of a long period comet, interstellar object or a back-up target in the form of a short-period comet. The target is not certain to be known before the launch in 2029. During the parking phase there may thus arise a scenario wherein a decision needs to be taken of whether to go for a particular comet or whether to discard that option in the hope that a better target will appear within a reasonable time frame later on. We present an expectation value-based formalism that could aid in the associated decision making provided that outlined requirements for its implementation exist.Comment: Accepted for publication in Planetary and Space Scienc

Oblique reflections in the Mars Express MARSIS data set:stable density structures in the Martian ionosphere

The Mars Advanced Radar for Subsurface and Ionospheric Sounding (MARSIS) onboard the European Space Agency's Mars Express (MEX) spacecraft routinely detects evidence of localized plasma density structures in the Martian dayside ionosphere. Such structures, likely taking the form of spatially extended elevations in the plasma density at a given altitude, give rise to oblique reflections in the Active Ionospheric Sounder data. These structures are likely related to the highly varied Martian crustal magnetic field. In this study we use the polar orbit of MEX to investigate the repeatability of the ionospheric structures producing these anomalous reflections, examining data taken in sequences of multiple orbits which pass over the same regions of the Martian surface under similar solar illuminations, within intervals lasting tens of days. Presenting three such examples, or case studies, we show for the first time that these oblique reflections are often incredibly stable, indicating that the underlying ionospheric structures are reliably reformed in the same locations and with qualitatively similar parameters. The visibility, or lack thereof, of a given oblique reflection on a single orbit can generally be attributed to variations in the crustal field within the ionosphere along the spacecraft trajectory. We show that, within these examples, oblique reflections are generally detected whenever the spacecraft passes over regions of intense near-radial crustal magnetic fields (i.e., with a “cusp-like” configuration). The apparent stability of these structures is an important feature that must be accounted for in models of their origin

Hybrid simulation of Titan's interaction with the supersonic solar wind during Cassini's T96 flyby

By applying a hybrid (kinetic ions and fluid electrons) simulation code, we study the plasma environment of Saturn's largest moon Titan during Cassini's T96 flyby on 1 December 2013. The T96 encounter marks the only observed event of the entire Cassini mission where Titan was located in the supersonic solar wind in front of Saturn's bow shock. Our simulations can quantitatively reproduce the key features of Cassini magnetic field and electron density observations during this encounter. We demonstrate that the large-scale features of Titan's induced magnetosphere during T96 can be described in terms of a steady state interaction with a high-pressure solar wind flow. About 40 min before the encounter, Cassini observed a rotation of the incident solar wind magnetic field by almost 90°. We provide strong evidence that this rotation left a bundle of fossilized magnetic field lines in Titan's ionosphere that was subsequently detected by the spacecraft.Fil: Feyerabend, Moritz. Georgia Institute Of Techology; Estados UnidosFil: Simon, Sven. Georgia Institute Of Techology; Estados UnidosFil: Neubauer, Fritz M.. Universitat Zu Köln; AlemaniaFil: Motschmann, Uwe. Deutsches Zentrum Fur Luft- Und Raumfahrt; Alemania. Technische Universitat Braunschweig; AlemaniaFil: Bertucci, Cesar. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; ArgentinaFil: Edberg, Niklas J. T.. Instiutet For Rymdfysik; SueciaFil: Hospodarsky, George B.. University Of Iowa; Estados UnidosFil: Kurth, William S.. University Of Iowa; Estados Unido

Mass-loading, pile-up, and mirror-mode waves at comet 67P/Churyumov-Gerasimenko

International audienceThe data from all Rosetta plasma consortium instruments and from the ROSINA COPS instrument are used to study the interaction of the solar wind with the outgassing cometary nucleus of 67P/Churyumov-Gerasimenko. During 6 and 7 June 2015, the interaction was first dominated by an increase in the solar wind dynamic pressure, caused by a higher solar wind ion density. This pressure compressed the draped magnetic field around the comet, and the increase in solar wind electrons enhanced the ionization of the outflow gas through collisional ionization. The new ions are picked up by the solar wind magnetic field, and create a ring/ring-beam distribution, which, in a high-β plasma, is unstable for mirror mode wave generation. Two different kinds of mirror modes are observed: one of small size generated by locally ionized water and one of large size generated by ionization and pickup farther away from the comet

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