Peter J. Chi

Key Points: The editors thank the 2025 peer reviewers

Interior Exploration using Seismic Investigations, Geodesy and Heat Transport (InSight) Fluxgate Magnetometer returned data from the Martian surface throughout the course of the InSight mission, between November 2018 and May 2022. Ultra‐low frequency (ULF) electromagnetic waves are commonly observed by InSight during nighttime hours. We present a collection of 444 nighttime ULF wave events with characteristic frequencies ranging from 1 to 16 mHz (periods from about 1 to 17 min), with a median frequency of about 7 mHz (period of about 140 s). Ultra‐low frequency wave activity is found across all nighttime hours, but the activity is more commonly observed after midnight local time. A subset of 104 InSight ULF wave events occur while Mars Atmosphere and Volatile EvolutioN (MAVEN) is located in the solar wind. During these events, the interplanetary magnetic field (IMF) deviates from its nominally expected orientation. We suggest that ULF waves are likely produced in the Martian magnetosphere by at least two different mechanisms and that the occurrence of the ULF waves on the surface is sensitive to the solar wind interaction with the Martian crustal fields. Further measurements by lander or orbiter missions will provide more information about the origin of ULF waves, how they reach the surface during the nighttime, and whether or not ULF waves can be used to perform magnetic sounding to study the subsurface of Mars.

Measurements of singly ionized oxygen () ions in the inner magnetosphere during geomagnetic storms are important because the ions affect various magnetospheric processes. We apply a magnetoseismic technique to Van Allen Probes data to statistically determine the spatial and temporal development of the region of elevated number density , referred to as the oxygen torus, during geomagnetic storms. This study is motivated by previous studies that reported magnetic local time (MLT) localization of the torus to the morning side. In our study, we first determine the frequencies of the fundamental through third harmonics of toroidal standing Alfvén waves to estimate the mass density and then use the electron density derived from plasma wave spectra to define the average ion mass (=). We obtain from by making an assumption about the number density relative to the number density. All quantities are evaluated in a 15 min moving data window that moves in 5 min steps. By generating ‐MLT maps of for different phases of 102 storms with SYMH minimum lower than nT, we find that a region of high appears on the morning side during the storm main phase and lasts for a few days. is also high on the morning side during the main phase, but this MLT skewing disappears during the recovery phase. Therefore, the MLT asymmetry of the oxygen torus depends on what parameter is considered.

Whitepaper #063 in the Decadal Survey for Solar and Space Physics (Heliophysics) 2024-2033. Main topics: basic research. Additional topics: planetary magnetospheres; ground-based missions/projects; space-based missions/projects.

Whitepaper #438 in the Decadal Survey for Solar and Space Physics (Heliophysics) 2024-2033. Main topics: space weather applications; basic research. Additional topics: space weather research/operations/research loop; ground-based missions/projects; space weather […]

Whitepaper #162 in the Decadal Survey for Solar and Space Physics (Heliophysics) 2024-2033. Main topics: space weather applications; basic research. Additional topics: space weather research/operations/research loop; space weather research/applications/operations pipeline; […]

Whitepaper #149 in the Decadal Survey for Solar and Space Physics (Heliophysics) 2024-2033. Main topics: space weather applications; basic research. Additional topics: planetary magnetospheres; inner heliosphere.

A document by Samuel Lihn. Click on the document to view its contents.

In the present study we examine three substorm events, Events 1–3, focusing on the spatio‐temporal development of auroral electrojets (AEJs) before auroral breakup. In Events 1 and 2, auroral breakup was preceded by the equatorward motion of an auroral form, and the ground magnetic field changed northward and southward in the west and east of the expected equatorward flow, respectively. Provided that these magnetic disturbances were caused by local ionospheric Hall currents, this feature suggests that the equatorward flow turned both eastward and westward as it reached the equatorward part of the auroral oval. The auroral breakup took place at the eastward‐turning and westward‐turning branches in Events 1 and 2, respectively, and after the auroral breakup, the westward AEJ enhanced only on the same side of the flow demarcation meridian. The zonal flow divergence is considered as an ionospheric manifestation of the braking of an earthward flow burst in the near‐Earth plasma sheet and subsequent dawnward and duskward turning. Therefore, in Events 1 and 2, the auroral breakup presumably mapped to the dawnward and duskward flow branches, respectively. Moreover, for Event 3, we do not find any pre‐onset auroral or magnetic features that can be associated with an equatorward flow. These findings suggest that the braking of a pre‐onset earthward flow burst itself is not the direct cause of substorm onset, and therefore, the wedge current system that forms at substorm onset is distinct from the one that is considered to form as a consequence of the flow braking.

The Moon and Mars have strong regional crustal magnetic fields as shown by the observations of orbiting spacecraft. These crustal magnetic fields indicate that a core dynamo was present in the past, and it is believed that rocks formed from cooling lava retain a memory of the strength and orientation of the magnetic field that existed during their solidification. However, a major hurdle in understanding the crustal magnetic field structure is the low spatial resolution limited by the altitude of the orbiting spacecraft. Rovers are well suited for exploring the detailed structure of the crustal magnetic fields, but they also present a technical challenge due to the necessity that sources of magnetic interference from the rover be removed from the measurements. We designed a compact rover dedicated to measuring the detailed spatial distribution of the surface magnetic field. The rover is equipped with an array of magnetic sensors mounted in a rectangular grid that aims to differentiate the rover components’ own magnetic fields from the ambient magnetic field. Another magnetic sensor is placed on top of an extendable arm to provide additional measurements for verifying the ambient magnetic field inferred from grid-point measurements. The rover consists of four wheels, a Raspberry Pi single-board computer, control circuitry, and a chassis that holds the magnetometers in a rectangular array. In the prototype of the rover, commercial small-scale microelectromechanical systems (MEMS) magnetometers are used for magnetic field measurements. The test results from these design features can provide a useful reference for future lunar or Martian surface missions with rover-based experiments that measure crustal magnetic fields.