Timing of the martian dynamo: New constraints for a core field 4.5 and 3.7 Ga ago

The absence of crustal magnetic fields above the martian basins Hellas, Argyre, and Isidis is often interpreted as proof of an early, before 4.1 billion years (Ga) ago, or late, after 3.9 Ga ago, dynamo. We revisit these interpretations using new MAVEN magnetic field data. Weak fields are present over the 4.5-Ga old Borealis basin, with the transition to strong fields correlated with the basin edge. Magnetic fields, confined to a near-surface layer, are also detected above the 3.7-Ga old Lucus Planum. We conclude that a dynamo was present both before and after the formation of the basins Hellas, Utopia, Argyre, and Isidis. A long-lived, Earth-like dynamo is consistent with the absence of magnetization within large basins if the impacts excavated large portions of strongly magnetic crust and exposed deeper material with lower concentrations of magnetic minerals.

Download Full-text

Magnetic Fields and Star Formation for the ANS Sample of Galaxies

Symposium - International Astronomical Union ◽

10.1017/s0074180900190072 ◽

1990 ◽

Vol 140 ◽

pp. 233-234

Author(s):

J. Stryczynski

Keyword(s):

Magnetic Field ◽

Star Formation ◽

Magnetic Fields ◽

Field Strength ◽

Magnetic Field Strength ◽

Field Data ◽

Spiral Galaxies ◽

Magnetic Field Data ◽

Uv Range

From the literature we collected radio and magnetic field data for the ANS spiral galaxies. We suggest that the groups of objects, as revealed in the UV range, do not differ in magnetic field strength, although statistics of the sample are very poor.

Download Full-text

Magnetic Fields in OH Maser Clouds

Symposium - International Astronomical Union ◽

10.1017/s0074180900026565 ◽

1974 ◽

Vol 60 ◽

pp. 275-292 ◽

Cited By ~ 1

Author(s):

R. D. Davies

Keyword(s):

Magnetic Field ◽

Angular Momentum ◽

Magnetic Fields ◽

Magnetic Flux ◽

Field Data ◽

Zeeman Splitting ◽

Galactic Rotation ◽

Magnetic Field Data ◽

The Magnetic Field ◽

Maser Sources

Observations of Class I OH maser sources show a range of features which are predicted on the basis of Zeeman splitting in a source magnetic field. Magnetic field strengths of 2 to 7 mG are derived for eight OH maser sources. The fields in all the clouds are directed in the sense of galactic rotation. A model of W3 OH is proposed which incorporates the magnetic field data. It is shown that no large amount of magnetic flux or angular momentum has been lost since the condensation from the interstellar medium began.

Download Full-text

Magnetic Archaeology of Early-type Stellar Dynamos

The Astrophysical Journal ◽

10.3847/1538-4357/ac2d2a ◽

2021 ◽

Vol 923 (1) ◽

pp. 104

Author(s):

Adam S. Jermyn ◽

Matteo Cantiello

Keyword(s):

Magnetic Field ◽

Magnetic Fields ◽

Mass Loss ◽

Bimodal Distribution ◽

Early Type ◽

Surface Magnetism ◽

Near Surface ◽

Early Type Stars ◽

Slow Evolution ◽

Weak Fields

Abstract Early-type stars show a bimodal distribution of magnetic field strengths, with some showing very strong fields (≳1 kG) and others very weak fields (≲10 G). Recently, we proposed that this reflects the processing or lack thereof of fossil fields by subsurface convection zones. Stars with weak fossil fields process these at the surface into even weaker dynamo-generated fields, while in stars with stronger fossil fields magnetism inhibits convection, allowing the fossil field to remain as is. We now expand on this theory and explore the timescales involved in the evolution of near-surface magnetic fields. We find that mass loss strips near-surface regions faster than magnetic fields can diffuse through them. As a result, observations of surface magnetism directly probe the frozen-in remains of the convective dynamo. This explains the slow evolution of magnetism in stars with very weak fields: these dynamo-generated magnetic fields evolve on the timescale of the mass loss, not that of the dynamo.

Download Full-text

UPWARD CONTINUATION OF TOTAL INTENSITY MAGNETIC FIELDS

Geophysics ◽

10.1190/1.1440138 ◽

1970 ◽

Vol 35 (5) ◽

pp. 920-926 ◽

Cited By ~ 4

Author(s):

Edwin S. Robinson

Keyword(s):

Magnetic Field ◽

Magnetic Fields ◽

Field Data ◽

Magnetic Field Data ◽

Upward Continuation ◽

Gravity And Magnetic ◽

Different Levels

Upward continuation of gravity and magnetic field data has been used in interpretation for over two decades. The additional perspective gained from viewing a field at different levels has been widely recognized as useful in interpreting subsurface anomaly sources.

Download Full-text

Fusion of gravity gradient and magnetic field data for discrimination of anomalies using deformation analysis

Geophysics ◽

10.1190/geo2010-0184.1 ◽

2012 ◽

Vol 77 (3) ◽

pp. F13-F20 ◽

Cited By ~ 4

Author(s):

Kamil Erkan ◽

Christopher Jekeli ◽

C. K. Shum

Keyword(s):

Magnetic Field ◽

Field Data ◽

Gravity Gradient ◽

Deformation Analysis ◽

Data Sets ◽

Low Density ◽

Gravity Gradiometry ◽

Near Surface ◽

Magnetic Field Data ◽

Efficient Integration

Gravity gradiometry and magnetometry methods are powerful noninvasive techniques for near-surface detection problems. Efficient integration of data from these techniques decreases the degree of nonuniqueness in geophysical interpretations. Deformation analysis is a powerful tool for comparison of two fields, which aids in this respect. We propose a fully quantitative approach, which uses the generalized theory of deformation for the geometric comparison of gravimetric and magnetic fields. The resulting deformation maps delineate regions where Poisson’s relation is violated between the two data sets and thus discriminate between air-filled cavities and other similar low-density/susceptibility geophysical sources. We present a practical corresponding algorithm that is robust in the sense that no prior knowledge of the physical properties of the subsurface is needed.

Download Full-text

An Augmented Iteratively Re-weighted and Refined Least Squares Method for lp Minimization Problem in Inverse Modeling of Potential Field Magnetic Data

Journal of Geological Research ◽

10.30564/jgr.v1i3.1316 ◽

2020 ◽

Vol 1 (3) ◽

Author(s):

Maysam Abedi

Keyword(s):

Magnetic Field ◽

Magnetic Susceptibility ◽

Least Squares ◽

Minimization Problem ◽

Potential Field ◽

Field Data ◽

Least Squares Method ◽

Porphyry Copper ◽

Magnetic Data ◽

Magnetic Field Data

The presented work examines application of an Augmented Iteratively Re-weighted and Refined Least Squares method (AIRRLS) to construct a 3D magnetic susceptibility property from potential field magnetic anomalies. This algorithm replaces an lp minimization problem by a sequence of weighted linear systems in which the retrieved magnetic susceptibility model is successively converged to an optimum solution, while the regularization parameter is the stopping iteration numbers. To avoid the natural tendency of causative magnetic sources to concentrate at shallow depth, a prior depth weighting function is incorporated in the original formulation of the objective function. The speed of lp minimization problem is increased by inserting a pre-conditioner conjugate gradient method (PCCG) to solve the central system of equation in cases of large scale magnetic field data. It is assumed that there is no remanent magnetization since this study focuses on inversion of a geological structure with low magnetic susceptibility property. The method is applied on a multi-source noise-corrupted synthetic magnetic field data to demonstrate its suitability for 3D inversion, and then is applied to a real data pertaining to a geologically plausible porphyry copper unit. The real case study located in Semnan province of Iran consists of an arc-shaped porphyry andesite covered by sedimentary units which may have potential of mineral occurrences, especially porphyry copper. It is demonstrated that such structure extends down at depth, and consequently exploratory drilling is highly recommended for acquiring more pieces of information about its potential for ore-bearing mineralization.

Download Full-text

A reexamination of “interstellar ion waves” previously identified in Pioneer 10 magnetic field data

Geophysical Research Letters ◽

10.1029/98gl02802 ◽

1998 ◽

Vol 25 (19) ◽

pp. 3721-3724 ◽

Cited By ~ 3

Author(s):

Neil Murphy ◽

Edward J. Smith ◽

Joyce Wolf ◽

Devrie S. Intriligator

Keyword(s):

Magnetic Field ◽

Field Data ◽

Magnetic Field Data ◽

Ion Waves ◽

Pioneer 10

Download Full-text

Ogo 5 magnetic-field data near the Earth's bow shock: A correlation with theory

Journal of Geophysical Research Atmospheres ◽

10.1029/ja077i004p00604 ◽

1972 ◽

Vol 77 (4) ◽

pp. 604-610 ◽

Cited By ~ 19

Author(s):

J. K. Guha ◽

D. L. Judge ◽

J. H. Marburger

Keyword(s):

Magnetic Field ◽

Field Data ◽

Bow Shock ◽

Magnetic Field Data ◽

Earth’S Bow Shock

Download Full-text

Using an induction coil sensor to indirectly measure the B-field response in the bandwidth of the transient electromagnetic method

Geophysics ◽

10.1190/1.1444837 ◽

2000 ◽

Vol 65 (5) ◽

pp. 1489-1494 ◽

Cited By ~ 34

Author(s):

Richard S. Smith ◽

A. Peter Annan

Keyword(s):

Magnetic Field ◽

Field Data ◽

Indirect Measurement ◽

Rate Of Change ◽

Induction Coil ◽

Voltage Response ◽

Magnetic Field Data ◽

Transient Electromagnetic ◽

Different Characteristics ◽

The Magnetic Field

The traditional sensor used in transient electromagnetic (EM) systems is an induction coil. This sensor measures a voltage response proportional to the time rate of change of the magnetic field in the EM bandwidth. By simply integrating the digitized output voltage from the induction coil, it is possible to obtain an indirect measurement of the magnetic field in the same bandwidth. The simple integration methodology is validated by showing that there is good agreement between synthetic voltage data integrated to a magnetic field and synthetic magnetic‐field data calculated directly. Further experimental work compares induction‐coil magnetic‐field data collected along a profile with data measured using a SQUID magnetometer. These two electromagnetic profiles look similar, and a comparison of the decay curves at a critical point on the profile shows that the two types of measurements agree within the bounds of experimental error. Comparison of measured voltage and magnetic‐field data show that the two sets of profiles have quite different characteristics. The magnetic‐field data is better for identifying, discriminating, and interpreting good conductors, while suppressing the less conductive targets. An induction coil is therefore a suitable sensor for the indirect collection of EM magnetic‐field data.

Download Full-text