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Gottingen, Germany

The Max Planck Institute for Solar System Research is a research institute in astronomy and astrophysics located in Göttingen, Germany, where it relocated in February 2014 from the nearby village of Lindau. The exploration of the solar system is the central theme for research done at this institute.MPS is a part of the Max Planck Society, which operates 80 research facilities in Germany.Over the last five years, members of the Institute have each year published about 270 articles in international journals and books and given 360 conference presentations. Wikipedia.

Christensen U.R.,Max Planck Institute for Solar System Research
Icarus | Year: 2015

Ganymede's internal magnetic field is dominated by the axial dipole. The measurements by the Galileo spacecraft only place an upper limit on the quadrupole moment. Ganymede's magnetic field has the lowest ratio of quadrupole power to dipole power for all known planetary dynamos, not only at the planetary surface but possibly also at the top of the dynamo region. The dynamo operates in a fluid iron core that probably contains a significant amount of sulfur. Crystallization of the core will then proceed from the top by formation of iron snow in a layer that develops a stable compositional gradient. Remelting of the snow at the bottom of this layer enriches the underlying fluid in iron and drives compositional convection. Here we explore the consequences for the dynamo process of this scenario by numerical modeling. Convection is driven by an imposed buoyancy flux at the top of a convecting core region that is surrounded by a conducting fluid shell with a strongly stabilizing density gradient. Only horizontal flow is allowed in the outer shell. It is shown that this is a valid approximation in the case where the stabilizing density contrast in the upper shell exceeds by far the unstable density contrast in the convecting region. We vary the basic control parameters, concentrating on the regime where the magnetic field is dominantly dipolar. Compared to reference cases without an extra layer above the dynamo, we find that a stable fluid conducting layer with a thickness of 100km or larger reduces the ratio of quadrupole power R2 to dipole power R1 by a factor of at least four. With a stable outer layer R2/R1 is compatible with the Galileo observations for all tested dipolar models, whereas in the absence of such layer R2/R1 is too large or at best marginally compatible. For plausible values of the buoyancy flux the models reproduce Ganymede's observed dipole moment. A stable layer that is comparable in thickness to the unstable region is found to promote a hemispherical type of dynamo whose field in incompatible with observations. This may indicate that the snow layer in Ganymede's core has a moderate depth extent. © 2014 Elsevier Inc.. Source

Van Noort M.,Max Planck Institute for Solar System Research
Astronomy and Astrophysics | Year: 2012

Context. When inverting solar spectra, image degradation effects that are present in the data are usually approximated or not considered. Aims. We develop a data reduction method that takes these issues into account and minimizes the resulting errors. Methods. By accounting for the diffraction PSF of the telescope during the inversions, we can produce a self-consistent solution that best fits the observed data, while simultaneously requiring fewer free parameters than conventional approaches. Results. Simulations using realistic MHD data indicate that the method is stable for all resolutions, including those with pixel scales well beyond those that can be resolved with a 0.5 m telescope, such as the Hinode SOT. Application of the presented method to reduce full Stokes data from the Hinode spectro-polarimeter results in dramatically increased image contrast and an increase in the resolution of the data to the diffraction limit of the telescope in almost all Stokes and fit parameters. The resulting data allow for detecting and interpreting solar features that have so far only been observed with 1m class ground-based telescopes. Conclusions. A new inversion method was developed that allows for accurate fitting of solar spectro-polarimetric imaging data over a large field of view, while simultaneously improving the noise statistics and spatial resolution of the results significantly. © 2012 ESO. Source

Marsch E.,Max Planck Institute for Solar System Research
Space Science Reviews | Year: 2012

The radial evolution of the velocity distribution functions of the protons, electrons and ions, as they were measured during the Helios mission in the solar wind between 0.3 and 1.0 AU, is discussed and analysed. Emphasis is placed on the detailed plasma measurements, and on the non-thermal features of the particles and the kinetic processes they undergo in the expanding solar wind. As the plasma is multi-component and nonuniform, complexity prevails and the observed distributions exhibit, owing to their low number densities, significant deviations from local thermal equilibrium, and reveal such suprathermal particles as the strahl electrons, as well as ion beams and temperature anisotropies. The distribution functions still carry imprints of their solar boundaries that are reflected locally, but also have ample free energy driving in situ plasma instabilities which are triggered and modulated by wave-particle interactions. The ion temperatures and their anisotropies and the non-adiabatic radial evolution of the solar wind internal energy are discussed in detail. © 2010 Springer Science+Business Media B.V. Source

Christensen U.R.,Max Planck Institute for Solar System Research
Physics of the Earth and Planetary Interiors | Year: 2011

Self-consistent models of the dynamo process in the Earth's core have reached a state where they can be used to understand specific morphological and temporal properties of the geomagnetic field. Even though several parameters in the models are far from Earth values, systematic parameter studies resulted in scaling laws that suggest that the dynamical regime in the models is not dissimilar to that in the core dynamo. In some dynamo models the magnetic field shows a close similarity with the structure of the geomagnetic field at the core-mantle boundary and the models are used to infer the underlying flow pattern inside the core. They support the concept of convection columns aligned with the rotation axis that concentrate magnetic flux into four strong lobes near ±65° latitude, and of rising plumes at the poles that are associated with low magnetic flux and westward vortex motion in the polar cap regions. Predictions for the field strength inside Earth's core from dynamo models and inferences from observations of short-term changes of the field and changes in Earth's rotation seem to converge at values of a few milliTesla. Dynamo models support the idea that the inhomogeneous thermal structure of the lower mantle has a significant influence on the dynamo and leads to a breaking of the longitudinal symmetry in the long-term geomagnetic field. In a limited range of control parameters the models show dipole polarity reversals that agree in detail with what is known about geomagnetic reversals, although the precise reversal mechanism in the models remains an open question. © 2011 Elsevier B.V. Source

Vasyliunas V.M.,Max Planck Institute for Solar System Research
Annales Geophysicae | Year: 2012

The conventional equations of ionospheric electrodynamics, highly succesful in modeling observed phenomena on sufficiently long time scales, can be derived rigorously from the complete plasma and Maxwell's equations, provided that appropriate limits and approximations are assumed. Under the assumption that a quasi-steady-state equilibrium (neglecting local dynamical terms and considering only slow time variations of external or aeronomic-process origin) exists, the conventional equations specify how the various quantities must be related numerically. Questions about how the quantities are related causally or how the stress equilibrium is established and on what time scales are not anwered by the conventional equations but require the complete plasma and Maxwell's equations, and these lead to a picture of the underlying physical processes that can be rather different from the commonly presented intuitive or ad hoc explanations. Particular instances include the nature of the ionospheric electric current, the relation between electric field and plasma bulk flow, and the interrelationships among various quantities of neutral-wind dynamo. © Author(s) 2012. Source

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