Space Science Reviews最新文献

NASA's Interstellar Mapping and Acceleration Probe (IMAP) mission provides extensive and well-coordinated new observations of the inner and outer heliosphere and scientific closure on two of the most important topics in Heliophysics: 1) the acceleration of charged particles and 2) the interaction of the solar wind with the local interstellar medium. These topics are intimately coupled because particles accelerated in the inner heliosphere propagate outward through the solar wind and mediate its interaction with the very local interstellar medium (VLISM). The IMAP mission is designed to address these topics, provide extensive new real-time measurements critical to Space Weather observations and predictions, and much more. IMAP's ten instruments are mounted on a simple, spinning spacecraft that orbits about the first Sun-Earth Lagrange point, L1, and repoints its Sun-facing solar arrays and spin axis toward the Sun each day. The instruments provide complete and synergistic observations that examine particle energization processes at 1 au while simultaneously probing the global heliospheric interaction with the VLISM. The 1 au in-situ observations include solar wind electrons and ions from solar wind through suprathermal energies, pickup and energetic ions, as well as the interplanetary magnetic field. IMAP provides Energetic Neutral Atom (ENA) global imaging of the outer heliosphere via ENAs from tens of eV up through hundreds of keV, as well as observations of interstellar neutral atoms traversing the heliosphere. IMAP also directly measures interstellar dust that enters the heliosphere and the solar-wind-modulated ultraviolet glow. This paper provides the mission overview for the full IMAP mission, acts as a roadmap to the other papers in this IMAP collection and provides the citable reference for the overall IMAP mission going forward.

Supplementary information: The online version contains supplementary material available at 10.1007/s11214-025-01224-z.

This article explores the different formation scenarios of the Kronian moons system in the context of a highly dissipative Saturn, with the objective of identifying the most likely of these scenarios. First, we review the diversity of objects - moons and rings - orbiting solar system giant planets, and the diversity of their architectures, which formation scenarios must reproduce. We then identify in this broader context the specific features of the Saturn system, such as the particularly large spectrum of its moon masses, the uniqueness of Titan and the presence of both dense and tenuous rings, before discussing the applicability of the different giant planet moon formation scenarios to the Saturn case. We discuss each of the most relevant scenarios and their respective merits. Finally, we tentatively propose a "favorite" scenario and we identify the key observations to be made by future space missions and/or Earth-based telescopic observations to validate this scenario or possibly alternative ones.

The detailed study of the global characteristics of collisionless magnetic reconnection that occurs at the magnetopause will be greatly enhanced by observations of plasma fluxes and fields within the low-altitude cusp region, as sampled by two spacecraft orbiting in tandem. The NASA Tandem Reconnection and Cusp Electrodynamics Reconnaissance Satellites (TRACERS) mission, a Heliophysics Small Explorer (SMEX) mission, will provide the necessary observations to enable significant progress to be made on understanding magnetic reconnection, especially in terms of its temporal versus spatial characteristics. This paper provides an overview of the TRACERS mission design and the trade studies conducted for the optimization of this design.

Information on the evolution of latitudinal profiles of the solar wind speed and density is one of the important elements needed to understand global observations of heliospheric neutral and charged particle populations performed by NASA's integrated heliospheric observatory Interstellar Mapping and Acceleration Probe (IMAP). This information is provided by the GLObal solar Wind Structure (GLOWS) experiment. GLOWS is a single-pixel Lyman- $\alpha$ photometer that observes the heliospheric backscatter glow emitted by interstellar neutral (ISN) H inside the heliosphere, illuminated by the solar Lyman- $\alpha$ emission. GLOWS features a specially designed optical entrance system with a baffle, collimator, and interference filter; a channeltron-based photon event detector; a digital processing unit (DPU) with custom-designed software that registers photon events and assembles lightcurves; a front-end electronics block that interfaces the detector and DPU; and the necessary power and voltage distribution system. Due to charge-exchange between ISN H and the solar wind, the helioglow bears imprints of the solar wind structure. Analysis of lightcurves observed daily along Sun-centered circles with a 75° radius in the sky yields profiles of intensities of the charge exchange reaction, which are decomposed into solar wind speed and density profiles at a Carrington period cadence. With them, it is possible to infer the shape of the heliosphere and its variation during the solar cycle and to determine the attenuation through re-ionization of energetic neutral atom fluxes between the ENA creation sites in the inner heliosheath and the IMAP ENA detectors.

The Analyzers for Cusp Ions (ACIs) on the TRACERS mission measure ion velocity distribution functions in the magnetospheric cusp from two closely spaced spacecraft in low Earth orbit. The precipitating and upflowing ion measurements contribute to the overarching goal of the TRACERS mission and are key to all three science objectives of the mission. ACI is a toroidal top-hat electrostatic analyzer on a spinning platform that provides full angular coverage with instantaneous 22.5° × ∼6° angular resolution for a single energy step. ACI has an ion energy range from ∼8 eV/e to 20,000 eV/e covered in 47 logarithmic-spaced energy steps with fractional energy resolution of ∼10%. It provides reasonably high cadence (312 ms) measurements of the ion energy-pitch angle distribution with good sensitivity and energy resolution, enabling detection of cusp boundaries and characterization of cusp ion steps.

In the last 30 years, many papers reported the almost simultaneous occurrence of magnetospheric fluctuations at different frequencies and latitudes (basically, in the range $f$ ≈ 1-5 mHz; $T$ ≈ 200-1000 s) and the possible existence and stability of sets of favorite frequencies (in particular: $f$ ${}_1\approx$ 1.3, $f$ ${}_2\approx$ 1.9, $f$ ${}_3\approx$ 2.6-2.7, and $f$ ${}_4\approx$ 3.2-3.4 mHz) has been proposed, determining controversial results. In the present paper we review these investigations focusing particular attention on several critical aspects that may have influenced the results and the comparison of these analyses (particularly, the correspondence between magnetospheric and solar wind fluctuations; the role of the short and long term variations of the solar wind and magnetospheric characteristics; the effects of the great variety of analytical methods adopted for the evaluation of power spectra and for the identification of relevant events). The results of this global analysis do not support the existence of a stable and persistent absolute set of favorite frequencies for magnetospheric oscillations; nevertheless, in the range of frequency explored by most investigations ( $f$ ≈ 1.5-4.0 mHz), they reveal a strong predominance of cases between $f$ ≈ 1.5-2.5 mHz, with percentages maximizing in the bin centered at $f$ = 2.0 mHz (a feature mostly due to events occurring at $f$ ≈ 1.9 mHz) and rapidly decreasing with increasing frequency; small evidence for an additional peak emerges at $f$ = 3.5 mHz; these aspects are much more explicit in the geomagnetic events than in the ionospheric and magnetospheric ones. Among other processes, the impact of the "mesoscale" solar wind density structures on the magnetosphere might be related with the onset of magnetospheric fluctuations at the observed frequencies.

Supplementary information: The online version contains supplementary material available at 10.1007/s11214-025-01166-6.

The Solar wind Magnetosphere Ionosphere Link Explorer (SMILE) was proposed to the Chinese Academy of Science (CAS) and the European Space Agency (ESA) following a joint call for science missions issued in January 2015. SMILE was proposed by a team of European and Chinese scientists, led by two mission Co-PIs, one from China and one from Europe. SMILE was selected in June 2015, and its budget adopted by the Chinese Academy of Sciences in November 2016 and the ESA Science Programme Committee in March 2019, respectively. SMILE will investigate the connection between the Sun and the Earth using a new technique that will image the magnetopause and polar cusps: the key regions where the solar wind impinges on Earth's magnetic field. Simultaneously, SMILE will image the auroras borealis in an ultraviolet waveband, providing long-duration continuous observations of the northern polar regions. In addition, the ion and magnetic field characteristics of the magnetospheric lobes, magnetosheath and solar wind will be measured by the in-situ instrument package. Here, we present the science goals, instruments and planned orbit. In addition the Working Groups that are supporting the preparation of the mission and the coordination with other magnetospheric missions are described.

Since the Voyager mission flybys in 1979, we have known the moon Io to be both volcanically active and the main source of plasma in the vast magnetosphere of Jupiter. Material lost from Io forms neutral clouds, the Io plasma torus and ultimately the extended plasma sheet. This material is supplied from Io's upper atmosphere and atmospheric loss is likely driven by plasma-interaction effects with possible contributions from thermal escape and photochemistry-driven escape. Direct volcanic escape is negligible. The supply of material to maintain the plasma torus has been estimated from various methods at roughly one ton per second. Most of the time the magnetospheric plasma environment of Io is stable on timescales from days to months. Similarly, Io's atmosphere was found to have a stable average density on the dayside, although it exhibits lateral (longitudinal and latitudinal) and temporal (both diurnal and seasonal) variations. There is a potential positive feedback in the Io torus supply: collisions of torus plasma with atmospheric neutrals are probably a significant loss process, which increases with torus density. The stability of the torus environment may be maintained by limiting mechanisms of either torus supply from Io or the loss from the torus by centrifugal interchange in the middle magnetosphere. Various observations suggest that occasionally (roughly 1 to 2 detections per decade) the plasma torus undergoes major transient changes over a period of several weeks, apparently overcoming possible stabilizing mechanisms. Such events (as well as more frequent minor changes) are commonly explained by some kind of change in volcanic activity that triggers a chain of reactions which modify the plasma torus state via a net change in supply of new mass. However, it remains unknown what kind of volcanic event (if any) can trigger events in torus and magnetosphere, whether Io's atmosphere undergoes a general change before or during such events, and what processes could enable such a change in the otherwise stable torus. Alternative explanations, which are not invoking volcanic activity, have not been put forward. We review the current knowledge on Io's volcanic activity, atmosphere, and the magnetospheric neutral and plasma environment and their roles in mass transfer from Io to the plasma torus and magnetosphere. We provide an overview of the recorded events of transient changes in the torus, address several contradictions and inconsistencies, and point out gaps in our current understanding. Lastly, we provide a list of relevant terms and their definitions.

Lucy is a NASA Discovery-class mission to send a highly capable and robust spacecraft to investigate primitive bodies near both the L₄ and L₅ Lagrange points with Jupiter; the Jupiter Trojan asteroids. This heretofore unexplored population of planetesimals from the outer planetary system holds vital clues to deciphering the history of the Solar System. Due to an unusual and fortuitous orbital configuration, Lucy will perform a comprehensive investigation that visits eight Trojans, including all the recognized taxonomic classes, a collisional family member and a near equal-mass binary. It will visit objects with diameters ranging from roughly 1 to 100 km. In particular, Lucy will perform flybys of (3548) Eurybates and its satellite Queta (L₄, C-type), (15094) Polymele and its currently unnamed satellite (L₄, P-type), (11351) Leucus (L₄, D-type), (21900) Orus (L₄, D-type), and the (617) Patroclus-Menoetius binary (L₅, P-types). This diverse array of targets will supply invaluable constraints on the formation and early dynamical evolution of the giant planets. In addition, Lucy will visit two main-belt asteroids, (152830) Dinkinesh and (52246) Donaldjohanson, in order to practice its encounters. Lucy's payload suite consists of a color camera and infrared imaging spectrometer, a high resolution panchromatic imager, and a thermal infrared spectrometer. Additionally, two spacecraft subsystems will also contribute to the science investigations: the terminal tracking cameras will supplement imaging during closest approach and the telecommunication subsystem will be used to measure the mass of the Trojans. Lucy launched on October 16, 2021 and will have encounters with the Trojans from August 2027 until March 2033.

Plasma flows with enhanced dynamic pressure, known as magnetosheath jets, are often found downstream of collisionless shocks. As they propagate through the magnetosheath, they interact with the surrounding plasma, shaping its properties, and potentially becoming geoeffective upon reaching the magnetopause. In recent years (since 2016), new research has produced vital results that have significantly enhanced our understanding on many aspects of jets. In this review, we summarise and discuss these findings. Spacecraft and ground-based observations, as well as global and local simulations, have contributed greatly to our understanding of the causes and effects of magnetosheath jets. First, we discuss recent findings on jet occurrence and formation, including in other planetary environments. New insights into jet properties and evolution are then examined using observations and simulations. Finally, we review the impact of jets upon interaction with the magnetopause and subsequent consequences for the magnetosphere-ionosphere system. We conclude with an outlook and assessment on future challenges. This includes an overview on future space missions that may prove crucial in tackling the outstanding open questions on jets in the terrestrial magnetosheath as well as other planetary and shock environments.