Search

Ultra‐low frequency (ULF) waves have been observed in the Mercury's magnetosphere by the Mariner 10 and MErcury Surface, Space ENvironment, GEochemistry and Ranging missions. The observed ∼2 s (∼0.6 Hz) period waves in the magnetic field are proposed to be generated by dynamic processes in the Mercury's magnetosphere. We investigate the Hermean ULF waves with a global hybrid model. We found evidence for ∼2‐s circularly polarized right‐handed waves in Mercury's magnetosphere at the closest approach of BepiColombo mission's first Mercury flyby in the model. The most intense wave power occurs on the dawn side closed magnetic field lines. These waves were found to be generated on the hemisphere which is magnetically directly connected to the interplanetary magnetic field on the dayside and to the foreshock region. It is therefore possible that the generation mechanism of these waves is associated with the precipitating ion flux or with the wave activity in the foreshock region. Plain Language Summary: Mercury's space environment includes several types of waves. Many of them are associated with the magnetosphere, which is the region dominated by the planet's intrinsic magnetic field and the solar wind. Low frequency waves at about 2‐s period were measured in the magnetic field by Mariner 10 and MErcury Surface, Space ENvironment, GEochemistry and Ranging spacecraft near the planet. The origin of these waves is proposed to be dynamical processes in the Mercury‐solar wind interaction. Here we investigate the 2‐s waves with a large‐scale computer simulation model, which covers global three‐dimensional space and resolves detailed solar wind ion movement and electromagnetic fields in the solar wind and magnetosphere around Mercury. Our analysis suggests that these waves occurred at the closest approach of BepiColombo mission's first Mercury flyby on 1 October 2021, in the dawn side of Mercury's magnetosphere. This location is connected via magnetic field lines to the solar wind in the day side of the planet. The waves may be generated in the solar wind before it encounters the Hermean magnetosphere or may be associated with ions traveling toward the planet's surface. Key Points: Ultra‐low frequency waves in Mercury's magnetosphere were investigated with a global hybrid modelAbout 2‐s period circularly polarized right‐handed waves occur on closed field lines along BepiColombo's first Mercury flyby in the modelThe waves are generated on the hemisphere which is directly magnetically connected to the interplanetary magnetic field and to the foreshock [ABSTRACT FROM AUTHOR]

Mercury's southern inner magnetosphere is an unexplored region as it was not observed by earlier space missions. In October 2021, BepiColombo mission has passed through this region during its first Mercury flyby. Here, we describe the observations of SERENA ion sensors nearby and inside Mercury's magnetosphere. An intermittent high-energy signal, possibly due to an interplanetary magnetic flux rope, has been observed downstream Mercury, together with low energy solar wind. Low energy ions, possibly due to satellite outgassing, were detected outside the magnetosphere. The dayside magnetopause and bow-shock crossing were much closer to the planet than expected, signature of a highly eroded magnetosphere. Different ion populations have been observed inside the magnetosphere, like low latitude boundary layer at magnetopause inbound and partial ring current at dawn close to the planet. These observations are important for understanding the weak magnetosphere behavior so close to the Sun, revealing details never reached before. BepiColombo mission had already two flybys of Mercury, over the total of six, as planned before entering the planet's orbit in 2025. Here, the authors show the first ion measurements of Mercury's inner southern magnetosphere during BepiColombo mission's first Mercury flyby. [ABSTRACT FROM AUTHOR]

The study of the micro-meteoroid environment is relevant to planetary science and space weathering of airless bodies, as the Moon or Mercury. In fact, the meteoroids hit directly the surfaces producing impact debris and vapor, thus contributing to shape the exosphere of the planet. This work is focused on the study and modelling of the Mercury's Ca exosphere formation through the process of Micro-Meteoroids Impact Vaporization (MMIV). The MESSENGER/NASA mission provided measurements of Mercury's Ca exosphere, allowing the study of its configuration and its seasonal variations. The observed Ca exhibited very high energies, with a scale height consistent with a temperature > 50,000 K, originated mainly on the dawn-side of the planet. It was suggested that the originating process is due to MMIV, but previous estimations were not able to justify the observed intensity and energy. We investigate the possible pathways to produce the high energy observed in the Ca exosphere and discuss about the generating mechanism. The most likely origin may be a combination of different processes involving the release of atomic and molecular surface particles. We use the exospheric Monte Carlo model by Mura et al. (2007) to simulate the 3-D spatial distribution of the Ca-bearing molecule and atomic Ca exospheres generated through the MMIV process, and we show that their morphology and intensity are consistent with the available MESSENGER observations if we consider a cloud quenching temperature < 3750 K. The results presented in this paper can be useful in the exospheric studies and in the interpretation of active surface release processes, as well as in the exosphere observations planning for the ESA-JAXA BepiColombo mission that will start its nominal mission phase in 2026. • Study and modelling of the Mercury's Ca exosphere formation through the process of Micro-Meteoroid Impact Vaporization (MMIV) • Main exospheric component at high altitudes is the energetic Ca from the shock-induced dissociative ionization and neutralization of Ca+ • Photo-dissociated Ca-bearing molecules provide non-negligible Ca contribution at low energies in the low-altitudes post-dawn region. • Simulated Ca exosphere along the planet orbit agrees with the MESSENGER/MASCS observations, when the plume temperature < 3750 K. [ABSTRACT FROM AUTHOR]

Observations of the sodium exosphere of Mercury show a peculiar yearly variability, with two intensity maxima at aphelion and perihelion. Here we present an analytical model for the total Na exosphere content, and we compare our results with ground-based observations. The model is able to reproduce the observed data, both in magnitude and in the seasonal variability. The combined effect of the planetary rotation with the modulation of sources and losses magnitude along the orbit, is able to produce a source of Na at dawn, which is needed to explain the observed maximum at aphelion. Also, we demonstrate that a process producing a consistent Na supply rate at the nightside, which can either be plasma or micrometeoroid precipitation, is needed as well. With the help of the model, we also propose a possible explanation for the dusk enhancement of Na that was seen in the MESSENGER data during the inbound leg of Mercury's orbit. • The analytical model of total exospheric Na content reproduces observations, both in magnitude and in seasonal variability. • A source of Na at dawn, driven by planetary rotation is needed to explain the peak of observed Na column density at aphelion. • A process producing Na supply rate in the nightside, either plasma and/or micrometeoroid precipitation, is needed. • We provide a possible explanation for the "dusk enhancement" observed by MESSENGER in the inbound leg of Mercury's orbit. [ABSTRACT FROM AUTHOR]