Some of the most sensitive methods of measuring magnetic fields use interactions of resonant light with atomic vapour. Recent developments in this vibrant field have led to improvements in sensitivity and other characteristics of atomic magnetometers, benefiting their traditional applications for measurements of geomagnetic anomalies and magnetic fields in space, and opening many new areas previously accessible only to magnetometers based on superconducting quantum interference devices. We review basic principles of modern optical magnetometers, discuss fundamental limitations on their performance, and describe recently explored applications for dynamical measurements of biomagnetic fields, detecting signals in NMR and MRI, inertial rotation sensing, magnetic microscopy with cold atoms, and tests of fundamental symmetries of nature.

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Optical magnetometry - eScholarship

Now more than ever, Gravitation and Spacetime, Second Edition, by Hans C. Ohanian and new coauthor Remo Ruffini, deserves John Wheeler's praise as "the best book on the market today of 500 pages or less on gravitation and general relativity." Gravitation and Spacetime has been thoroughly updated with the most exciting finds and hottest theoretical topics in general relativity and cosmology. Highlights of the revision include the rise and fall of the fifth force, principles and applications of gravitational lensing, COBE's spectacular confirmation of the blackbody spectrum of the cosmic thermal radiation, theories of dark matter and inflation, and the early universe as a testing ground for particle physicists' unification theories, and much, much more. The ideal choice for a graduate-level introduction to general relativity, Gravitation and Spacetime is also suitable for an advanced undergaduate course.

Gravitation and spacetime.

Planetary magnetic fields

The MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft, launched on August 3, 2004, is nearing the halfway point on its voyage to become the first probe to orbit the planet Mercury. The mission, spacecraft, and payload are designed to answer six fundamental questions regarding the innermost planet: (1) What planetary formational processes led to Mercury’s high ratio of metal to silicate? (2) What is the geological history of Mercury? (3) What are the nature and origin of Mercury’s magnetic field? (4) What are the structure and state of Mercury’s core? (5) What are the radar-reflective materials at Mercury’s poles? (6) What are the important volatile species and their sources and sinks near Mercury? The mission has focused to date on commissioning the spacecraft and science payload as well as planning for flyby and orbital operations. The second Venus flyby (June 2007) will complete final rehearsals for the Mercury flyby operations in January and October 2008 and September 2009. Those flybys will provide opportunities to image the hemisphere of the planet not seen by Mariner 10, obtain high-resolution spectral observations with which to map surface mineralogy and assay the exosphere, and carry out an exploration of the magnetic field and energetic particle distribution in the near-Mercury environment. The orbital phase, beginning on March 18, 2011, is a one-year-long, near-polar-orbital observational campaign that will address all mission goals. The orbital phase will complete global imaging, yield detailed surface compositional and topographic data over the northern hemisphere, determine the geometry of Mercury’s internal magnetic field and magnetosphere, ascertain the radius and physical state of Mercury’s outer core, assess the nature of Mercury’s polar deposits, and inventory exospheric neutrals and magnetospheric charged particle species over a range of dynamic conditions. Answering the questions that have guided the MESSENGER mission will expand our understanding of the formation and evolution of the terrestrial planets as a family.

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MESSENGER Mission Overview

During Cassini9s initial orbit, we observed a dynamic magnetosphere composed primarily of a complex mixture of water-derived atomic and molecular ions. We have identified four distinct regions characterized by differences in both bulk plasma properties and ion composition. Protons are the dominant species outside about 9 R S (where R S is the radial distance from the center of Saturn), whereas inside, the plasma consists primarily of a corotating comet-like mix of water-derived ions with ∼3% N + . Over the A and B rings, we found an ionosphere in which O 2 + and O + are dominant, which suggests the possible existence of a layer of O 2 gas similar to the atmospheres of Europa and Ganymede.

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Composition and dynamics of plasma in Saturn's magnetosphere.

Cassini's successful orbit insertion has provided the first examination of Saturn's magnetosphere in 23 years, revealing a dynamic plasma and magnetic environment on short and long time scales. There has been no noticeable change in the internal magnetic field, either in its strength or its near-alignment with the rotation axis. However, the external magnetic field is different compared with past spacecraft observations. The current sheet within the magnetosphere is thinner and more extended, and we observed small diamagnetic cavities and ion cyclotron waves of types that were not reported before.

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Cassini magnetometer observations during Saturn orbit insertion.

. The existence of a ring current inside Saturn's magnetosphere was first suggested by Smith et al. (1980) and Ness et al. (1981, 1982), in order to explain various features in the magnetic field observations from the Pioneer 11 and Voyager 1 and 2 spacecraft. Connerney et al. (1983) formalized the equatorial current model, based on previous modelling work of Jupiter's current sheet and estimated its parameters from the two Voyager data sets. Here, we investigate the model further, by reconsidering the data from the two Voyager spacecraft, as well as including the Pioneer 11 flyby data set. First, we obtain, in closed form, an analytic expression for the magnetic field produced by the ring current. We then fit the model to the external field, that is the difference between the observed field and the internal magnetic field, considering all the available data. In general, through our global fit we obtain more accurate parameters, compared to previous models. We point out differences between the model's parameters for the three flybys, and also investigate possible deviations from the axial and planar symmetries assumed in the model. We conclude that an accurate modelling of the Saturnian disk current will require taking into account both of the temporal variations related to the condition of the magnetosphere, as well as non-axisymmetric contributions due to local time effects. Key words. Magnetospheric physics (current systems; planetary magnetospheres; plasma sheet)

/pdf/modelling-of-the-ring-current-in-saturn-s-magnetosphere-2dgrw9mt4s.pdf

Modelling of the ring current in Saturn's magnetosphere

Mercury's thermoelectric dynamo model revisited

[1] Analysis of magnetic field data from the Pioneer 11, Voyager 1 and Voyager 2 spacecraft produced the first models of Saturn's internal field One striking feature of these models is the lack of non axisymmetric terms, which poses strong constraints on the dynamo mechanism Resolution of the internal field using magnetic field data from different epochs is complicated by the uncertainty in our knowledge of the planetary rotation rate By reanalyzing the flyby data, using modern inversion techniques, we derive the first tentative direct measurement of the rotation rate of the magnetic field The measured rotation period agrees within 06 s with the value obtained from remote radio emission measurements, and its uncertainty is reduced to ±24 s From an inversion of all available magnetic field data, we conclude that it is premature to exclude the presence of non-axisymmetric terms when describing the internal planetary field, and in particular we find a significant dipole tilt of 017°

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2004GL020194

Rotation rate of Saturn's interior from magnetic field observations

The planet closest to the Sun, Mercury, is the subject of renewed attention among planetary scientists, as two major space missions will visit it within the next decade. These will be the first to return to Mercury, after the flybys by NASA's Mariner 10 spacecraft in 1974-5. The difficulties of observing this planet from the Earth make such missions necessary for further progress in understanding its origin, evolution and present state. This review provides an overview of what is known about Mercury and what are the major outstanding issues. Mercury's orbital and rotation periods are in a unique 2:3 resonance; an analysis of the orbital dynamics of Mercury is presented here, as well as Mercury's special role in testing theories of gravitation. These derivations provide a good insight into the complexities of planetary motion in general, and how, in the case of Mercury, its proximity to the Sun can be described and exploited in terms of general relativity. Mercury's surface, superficially similar to that of the Moon, presents intriguing differences, representing a different, and more complex history in which the role of early volcanism remains to be clarified and understood. Mercury's interior presents the most important puzzles: it has the highest uncompressed density among the terrestrial planets, implying a very large, mostly iron core. This does not appear to be the completely solidified yet, as Mariner 10 found a planetary magnetic field that is probably generated by an internal dynamo, in a liquid outer layer of the large iron core. The current state of the core, once established, will provide a constraint for its evolution from the time of the planet's formation. Mercury's environment is highly variable. There is only a tenuous exosphere around Mercury; its source is not well understood, although there are competing models for its formation and dynamics. The planetary magnetic field appears to be strong enough to form a magnetosphere around the planet, through its interaction with the solar wind. This magnetosphere may have similarities with that of the Earth, but is more likely to be dominated by global dynamics that could make it collapse at least at the time of large solar outbursts. The future understanding of the planet will now await the arrival of the new space missions. The review concludes with a brief description of these missions.

https://iopscience.iop.org/article/10.1088/0034-4885/65/4/202/pdf

Giacomo Giampieri

Papers

Cassini magnetometer observations during Saturn orbit insertion.

Modelling of the ring current in Saturn's magnetosphere

Mercury's thermoelectric dynamo model revisited

Rotation rate of Saturn's interior from magnetic field observations

Mercury: the planet and its orbit