The Scientific Investigation of Unidentified Aerial Phenomena (UAP) Using Multimodal Ground-based Observatories

Peer reviewedPublisher PD

Unveiling Earth's Hidden Magnetization

International audienceRock magnetization carries information about rocks' properties, Earth's tectonic history, and evolution of its core magnetic field. One way to study Earth's magnetization is through the magnetic signal it generates, known as the lithospheric magnetic field. Although there exist global lithospheric magnetic field models of high spatial resolution, this path has not yet been very fruitful because of an important limitation: only part of the magnetization is visible, that is, produces an observable magnetic field signal. We refer to the remaining part of the magnetization as the hidden magnetization, and we recover it from a lithospheric magnetic field model under a few reasonable assumptions. We find that Earth's hidden magnetization at high and middle latitudes is very similar, both in intensity and shape, to Earth's visible magnetization. At low latitudes, the estimated hidden magnetization relies on a priori information and can be very different from the visible one

Hand Magnets and the Destruction of Ancient Meteorite Magnetism

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A new high-resolution geomagnetic field model for southern Africa

Earth’s magnetic field is a dynamic, changing phenomenon. The geomagnetic field consists of contributions from several sources, of which the main field originating in Earth’s core makes up the bulk. On regional and local scales at Earth’s surface, the lithospheric field can make a substantial contribution to the overall field and therefore needs to be considered in field models. A locally derived regional core field model, named HMOREG, has been shown to give accurate predictions of the southern African region. In this study, a new regional field model called the South African Regional Core and Crust model (SARCC) is introduced. This is the first time that a local lithospheric model, estimated by employing the revised spherical cap harmonic analysis modelling method, has been combined with the core component of CHAOS-6, a global field model. It is compared here with the existing regional field model as well as with global core field models. The SARCC model shows small-scale variations that are not present in the other three models. Including a lithospheric magnetic field component likely contributed to the better performance of the SARCC model when compared to other global and local field models. The SARCC model showed a 33% reduction in error compared to surface observations obtained from field surveys and INTERMAGNET stations in the Y component, and HMOREG showed a 7% reduction in error compared to the global field models. The new model can easily be updated with global geomagnetic models that incorporate the most recent, state-of-the-art core and magnetospheric field models. Significance: Earth’s magnetic field is an integral part of many current navigational methods in use. Updates of geomagnetic field models are required to ensure the accuracy of maps, navigation, and positioning information. The SARCC regional geomagnetic field model introduced here was compared with global geomagnetic field models, and the inclusion of a lithospheric magnetic field component likely contributed to the better performance of the SARCC model. This regional model of southern Africa could easily be updated on a regular basis, and used for high-resolution information on the Earth’s magnetic field for the wider scientific community

Constraints on the Spatial Distribution of Lunar Crustal Magnetic Sources From Orbital Magnetic Field Data

International audienceSpacecraft measurements show that the crust of the Moon is heterogeneously magnetized. The sources of these magnetic anomalies are yet not fully understood, with most not being related to known geological structures or processes. Here, we use an inversion methodology that relies on the assumption of unidirectional magnetization, commonly referred to as Parker's method, to elucidate the origin of the magnetic sources by constraining the location and geometry of the underlying magnetization. This method has been used previously to infer the direction of the underlying magnetization but it has not been tested as to whether it can infer the geometry of the source. The performance of the method is here assessed by conducting a variety of tests, using synthetic magnetized bodies of different geometries mimicking the main geological structures potentially magnetized within the lunar crust. Results from our tests show that this method successfully localizes and delineates the two-dimensional surface projection of subsurface three-dimensional magnetized bodies, provided their magnetization is close to unidirectional and the magnetic field data are of sufficient spatial resolution and reasonable signal-to-noise ratio. We applied this inversion method to two different lunar magnetic anomalies, the Mendel-Rydberg impact basin and the Reiner Gamma swirl. For Mendel-Rydberg, our analysis shows that the strongest magnetic sources are located within the basin's inner ring, whereas for Reiner Gamma, the strongest magnetic sources form a narrow dike-like body that emanates from the center of the Marius Hills volcanic complex. Plain Language Summary Magnetometers onboard spacecraft have detected magnetic field signals originating from the lunar crust. These signals are known as magnetic anomalies and are generated by rocks that are permanently magnetized. Lunar magnetic anomalies are distributed heterogeneously over the lunar surface and the geological processes that gave rise to them is under debate. By inferring the shape of the underlying magnetized material, we can constrain these processes and shed light on the Moon's geological history. In this study, we evaluate the ability of a methodology up to now used to infer the direction of the magnetization, to recover the location and shape of the magnetized material. Through a series of tests, we show that this method can constrain the shape of the source of a magnetic anomaly, provided that the respective part of the crust is magnetized along a common direction. We then apply the method to two lunar magnetic anomalies. The inferred shape and location are in good agreement with the associated geological features and suggest that one originated by an impact event and the other by volcanic activity. Future applications can focus on constraining the origin of the many lunar magnetic anomalies that are not associated with visible geological features

Mars’ Crustal Magnetic Field

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