scholarly journals Magnetically induced termination of giant planet formation

2018 ◽  
Vol 619 ◽  
pp. A165 ◽  
Author(s):  
A. J. Cridland
Keyword(s):  
Magnetic Field ◽  
Cross Section ◽  
Planet Formation ◽  
Giant Planet ◽  
Effective Cross Section ◽  
Cold Start ◽  
Population Synthesis ◽  
Hot Start ◽  
Gas Accretion ◽  
Planetary Magnetic Field

Here a physical model for terminating giant planet formation is outlined and compared to other methods of late-stage giant planet formation. As has been pointed out before, gas accreting into a gap and onto the planet will encounter the planetary dynamo-generated magnetic field. The planetary magnetic field produces an effective cross section through which gas is accreted. Gas outside this cross section is recycled into the protoplanetary disk, hence only a fraction of mass that is accreted into the gap remains bound to the planet. This cross section inversely scales with the planetary mass, which naturally leads to stalled planetary growth late in the formation process. We show that this method naturally leads to Jupiter-mass planets and does not invoke any artificial truncation of gas accretion, as has been done in some previous population synthesis models. The mass accretion rate depends on the radius of the growing planet after the gap has opened, and we show that so-called hot-start planets tend to become more massive than cold-start planets. When this result is combined with population synthesis models, it might show observable signatures of cold-start versus hot-start planets in the exoplanet population.

scholarly journals The effective cross section of the oriented hydrogen atom

1927 ◽  
Vol 114 (767) ◽  
pp. 212-221 ◽  
Keyword(s):  
Magnetic Field ◽  
Dielectric Constant ◽  
Cross Section ◽  
Effective Cross Section ◽  
Inert Gases ◽  
Zinc Cadmium ◽  
Electron Group ◽  
Closed Electron ◽  
At Will

1. Evidence has recently been accumulating that atoms may show an isotropy far greater than would be anticipated on the basis of the atom model developed by Bohr and Sommerfeld; a suggestion which is thrown into strong relief by the examination of matter under conditions of space quantisation in a magnetic field. Evidently, the possibility of orienting at will the momentum axes of certain atoms in a prescribed direction in space offers an ideal means of investigating atomic symmetry. One must be careful, however, in drawing deductions from observations of this kind. Sommerfeld has clearly shown that those atoms which possess a closed electron group in the sense of the Stoner classification of electron levels cannot orient when in the normal state. The experiments of Stern and Gerlach on zinc, cadmium, mercury, tin and lead are in excellent agreement with this idea. In this regard, the observations of, for example, Dymond on the excitation of helium by electron impacts, Rusch§ on the cross section of argon, and of Weatherby and Wolf|| on the dielectric constant of helium cannot be interpreted as indicating marked atomic isotropy; because the inert gases possess a closed group.

scholarly journals Are the observed gaps in protoplanetary discs caused by growing planets?

2019 ◽  
Vol 488 (3) ◽  
pp. 3625-3633 ◽  
Author(s):  
N Ndugu ◽  
B Bitsch ◽  
E Jurua
Keyword(s):  
Planet Formation ◽  
Dust Particles ◽  
Type I ◽  
Type Ii ◽  
Population Synthesis ◽  
Small Pressure ◽  
Planetary Mass ◽  
Planet Migration ◽  
Gas Accretion ◽  
Protoplanetary Discs

ABSTRACT Recent detailed observations of protoplanetary discs revealed a lot of substructures that are mostly ring like. One interpretation is that these rings are caused by growing planets. These potential planets are not yet opening very deep gaps in their discs. These planets instead form small gaps in the discs to generate small pressure bumps exterior to their orbits that stop the inflow of the largest dust particles. In the pebble accretion paradigm, this planetary mass corresponds to the pebble isolation mass, where pebble accretion stops and efficient gas accretion starts. We perform planet population synthesis via pebble and gas accretion including type-I and type-II migration. In the first stage of our simulations, we investigate the conditions necessary for planets to reach the pebble isolation mass and compare their position to the observed gaps. We find that in order to match the gap structures 2000ME in pebbles is needed, which would be only available for the most metal-rich stars. We then follow the evolution of these planets for a few Myr to compare the resulting population with the observed exoplanet populations. Planet formation in discs with these large amounts of pebbles results in mostly forming gas giants and only very little super-Earths, contradicting observations. This leads to the conclusions that either (i) the observed discs are exceptions, (ii) not all gaps in observed discs are caused by planets, or (iii) that we miss some important ingredients in planet formation related to gas accretion and/or planet migration.

EFFECTS OF SPACE CHARGE ON THE "EFFECTIVE CROSS SECTION"

1979 ◽  
Vol 40 (C7) ◽  
pp. C7-755-C7-756
Author(s):  
N. S. Kopeika ◽  
T. Karcher ◽  
C.S. Ih.
Keyword(s):  
Space Charge ◽  
Cross Section ◽  
Effective Cross Section

Giant planet formation with pebble accretion

Icarus ◽  
2014 ◽  
Vol 233 ◽  
pp. 83-100 ◽  
Author(s):  
J.E. Chambers
Keyword(s):  
Planet Formation ◽  
Giant Planet

scholarly journals Efficiency of thermal conduction in a magnetized circumgalactic medium

2021 ◽  
Vol 502 (1) ◽  
pp. 1263-1278
Author(s):  
Richard Kooij ◽  
Asger Grønnow ◽  
Filippo Fraternali
Keyword(s):  
Magnetic Field ◽  
Thermal Conduction ◽  
Large Temperature ◽  
Gas Condensation ◽  
Circumgalactic Medium ◽  
Field Lines ◽  
Gas Accretion ◽  
Cloud Evolution ◽  
The Magnetic Field ◽  
Cold Gas

ABSTRACT The large temperature difference between cold gas clouds around galaxies and the hot haloes that they are moving through suggests that thermal conduction could play an important role in the circumgalactic medium. However, thermal conduction in the presence of a magnetic field is highly anisotropic, being strongly suppressed in the direction perpendicular to the magnetic field lines. This is commonly modelled by using a simple prescription that assumes that thermal conduction is isotropic at a certain efficiency f < 1, but its precise value is largely unconstrained. We investigate the efficiency of thermal conduction by comparing the evolution of 3D hydrodynamical (HD) simulations of cold clouds moving through a hot medium, using artificially suppressed isotropic thermal conduction (with f), against 3D magnetohydrodynamical (MHD) simulations with (true) anisotropic thermal conduction. Our main diagnostic is the time evolution of the amount of cold gas in conditions representative of the lower (close to the disc) circumgalactic medium of a Milky-Way-like galaxy. We find that in almost every HD and MHD run, the amount of cold gas increases with time, indicating that hot gas condensation is an important phenomenon that can contribute to gas accretion on to galaxies. For the most realistic orientations of the magnetic field with respect to the cloud motion we find that f is in the range 0.03–0.15. Thermal conduction is thus always highly suppressed, but its effect on the cloud evolution is generally not negligible.

scholarly journals Planetary Magnetic Fields and Habitability in Super Earths

2018 ◽  
Vol 27 (1) ◽  
pp. 183-231 ◽  
Author(s):  
Pablo Cuartas-Restrepo
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Scaling Laws ◽  
Thermal Evolution ◽  
Solid Core ◽  
Direct Influence ◽  
Physical Processes ◽  
Planetary Magnetic Fields ◽  
Planetary Magnetic Field ◽  
Planetary Dynamos

Abstract This work seeks to summarize some special aspects of a type of exoplanets known as super-Earths (SE), and the direct influence of these aspects in their habitability. Physical processes like the internal thermal evolution and the generation of a protective Planetary Magnetic Field (PMF) are directly related with habitability. Other aspects such as rotation and the formation of a solid core are fundamental when analyzing the possibilities that a SE would have to be habitable. This work analyzes the fundamental theoretical aspects on which the models of thermal evolution and the scaling laws of the planetary dynamos are based. These theoretical aspects allow to develop models of the magnetic evolution of the planets and the role played by the PMF in the protection of the atmosphere and the habitability of the planet.

scholarly journals Forming terrestrial planets and delivering water

2015 ◽  
Vol 11 (A29B) ◽  
pp. 427-430
Author(s):  
Kevin J. Walsh
Keyword(s):  
Planet Formation ◽  
Semimajor Axis ◽  
Giant Planet ◽  
Terrestrial Planet ◽  
Giant Planets ◽  
Asteroid Belt ◽  
Terrestrial Planets ◽  
The Earth ◽  
Building Models ◽  
Rich Material

AbstractBuilding models capable of successfully matching the Terrestrial Planet's basic orbital and physical properties has proven difficult. Meanwhile, improved estimates of the nature of water-rich material accreted by the Earth, along with the timing of its delivery, have added even more constraints for models to match. While the outer Asteroid Belt seemingly provides a source for water-rich planetesimals, models that delivered enough of them to the still-forming Terrestrial Planets typically failed on other basic constraints - such as the mass of Mars.Recent models of Terrestrial Planet Formation have explored how the gas-driven migration of the Giant Planets can solve long-standing issues with the Earth/Mars size ratio. This model is forced to reproduce the orbital and taxonomic distribution of bodies in the Asteroid Belt from a much wider range of semimajor axis than previously considered. In doing so, it also provides a mechanism to feed planetesimals from between and beyond the Giant Planet formation region to the still-forming Terrestrial Planets.

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