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Abstract Magnetotail current sheet (CS) flapping is a universal plasma phenomenon observed at multiple planets, yet its triggering mechanisms remain poorly understood outside of Earth. At Mars, single‐spacecraft observations have also reported tail flapping, but the processes responsible for its onset have never been identified. In this study, we investigate the potential correlation between magnetic reconnection and magnetotail flapping using multipoint measurements from Mars Atmosphere and Volatile EvolutioN (MAVEN) and Tianwen‐1 (TW‐1) missions. We analyze an example event in which MAVEN observed a reconnection‐associated CS crossing in the near tail while TW‐1 simultaneously detected CS flapping further downtail. A statistical survey of joint observations from November 2021 to February 2024 identifies that about two‐thirds of TW‐1 flapping events coincide with reconnection signatures observed by MAVEN. Multiple magnetic flux ropes were also detected before or during flapping intervals, similar to previous observations at Earth, suggesting that reconnection‐generated magnetic flux ropes may propagate tailward and drive plasma instabilities that trigger the tail flapping at Mars. These results provide the first multipoint evidence of a potential statistical correlation between magnetic reconnection and magnetotail flapping at Mars, enabling us to explore the potential triggering mechanism of magnetotail flapping. Our findings also offer new insights into Martian magnetotail dynamics and broaden the comparative understanding of this fundamental plasma process across planetary environments.
Volatile loss from exoplanetary atmospheres and its possible implications for the longevity of habitable surface conditions is a topic of vigorous debate currently. The vast majority of the habitable zone terrestrial-like exoplanets known to date orbit low-mass M- and K-dwarf stars and are subject to the conditions drastically different to those of terrestrial planets in the Solar System. In particular, they orbit far closer to their host stars than similar planets around G-dwarfs similar to the Sun. Therefore they receive higher X-ray and UV fluxes, even though luminosities of M- and K-dwarfs are lower than those of heavier stars. Furthermore, due to their slower evolution, M-dwarfs retain high activity on the gigayear timescales. The combination of these two effects has led to claims that most terrestrial planets orbiting M-dwarfs may have their atmospheres stripped from the higher X-ray and UV fluxes of their host stars. Opposing this are researchers who point out that volatile inventories for terrestrial exoplanets are ill-constrained, and hence, they may be able to “weather the storm” of these higher X-ray and UV fluxes. In this article, we focus on exploring volatile loss in the upper atmospheres of terrestrial planets in our solar system and applications to those in exoplanetary systems around stars of different types.
Ions with mass-to-charge ratios from 2 to 150 have been measured in the Martian ionosphere by the Neutral Gas and Ion Mass Spectrometer (NGIMS) onboard the Mars Atmosphere and Volatile EvolutioN (MAVEN) mission. Among these, protonated species at 31, 33, and 41 atomic mass units (amu) are observed at densities significantly higher than those predicted by photochemical models. In this study, we combine photochemical modelling with NGIMS measurements to investigate these discrepancies in the dayside ionosphere of Mars. For 41 amu ions, the photochemical model predicts ArH+ densities more than one order of magnitude lower than NGIMS measurements. For 31 and 33 amu ions, modelled densities of HNO+ and HO2+ are three orders of magnitude lower than observed values. We find that the vertical profiles reveal striking similarities among (a) the 31, 32, and 33 amu channels and (b) the 41, 42, 43, and 44 amu channels, which cannot be fully explained by interlinked chemical pathways and contributions from oxygen isotopes. Instead, we suggest that instrumental effects, specifically mass channel cross-talk from the strong 32 and 44 amu, provide a plausible explanation for the anomalously high densities reported at 31, 33, and 41 amu.
Context. The escape of oxygen ions from Mars has played a crucial role in the planet’s long-term atmospheric evolution and habitability. The crustal magnetic fields influence ion escape, but the exact role remains debated. Previous studies have presented contrasting conclusions, suggesting that the crustal fields may either suppress or enhance oxygen ion escape. To date, the extent and mechanisms of this influence remain insufficiently understood. Aims. This study aims to investigate the influence of the Martian crustal magnetic fields on the oxygen ion escape at Mars. Methods. Several groups of 3D global hybrid simulations of Mars-solar wind interaction were performed, with the escaping oxygen ion trajectories traced. The results from the simulations with or without the crustal fields and under different interplanetary magnetic field conditions were then compared. Results. The simulation results show that the presence of crustal fields enhances the ionospheric oxygen ion escape, while the exospheric oxygen ion escape rate remains largely unaffected. The crustal magnetic fields alter the local electric and magnetic environments and, subsequently, modify the local oxygen ion density and flow direction in the ionosphere. First, the steep magnetic inclination and large magnetic strength in crustal field regions increase the density of low-altitude ionospheric oxygen ions and facilitate their outward transport, thereby promoting ion escape. Second, the crustal fields modify the local electric field structure, which also affects ion acceleration and escape. When strong crustal fields are located on the dayside, their obstruction of the upstream plasma flow weakens the dayside radial electric field at low altitudes in the southern hemisphere. The weakened electric field tends to assist or reduce ion escape, depending on whether it points toward or away from Mars, respectively. In any case, the influence of the magnetic field topology change (the steep magnetic inclination and large magnetic strength) in crustal field regions dominates the effect of weakened electric field, resulting in a higher escape rate than that without the crustal fields. Additionally, when strong crustal fields are on the nightside, the dayside moderate crustal fields still enhance the local density and outward transport of ionospheric oxygen ions, while their impact on the local electric field remains limited. The net effect is enhanced ion escape over the +E hemisphere where the solar wind motional electric field points away from Mars.
Comet Interceptor is an ESA science mission with payload contributions from ESA Member States and with an international participation by JAXA. It is the first mission that is being designed, built, and potentially launched before its target is known. This approach will enable the spacecraft to perform the first mission to a Long Period Comet from the Oort Cloud, as these comets have fleeting visits to the inner Solar System lasting only months to years from first discovery, too short for the usual process of mission development to be followed. In this paper we describe a number of factors that need to be considered in selecting a target for the mission, including scientific, orbital, spacecraft and instrument constraints, and discussion of different prioritisation strategies. We find that, in the case where we have a choice of targets, our decisions will mostly be driven by orbital information, which we will have relatively early on, with information on the activity level of the comet an important but secondary consideration. As cometary activity levels are notoriously hard to predict based on early observations alone, this prioritisation / decision approach based more on orbits gives us confidence that a good comet that is compatible with the spacecraft constraints will be selectable with sufficient warning time to allow the mission to intercept it.
