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961.
962.
963.
Europa is bombarded by intense radiation that erodes the surface, launching molecules into a thin “atmosphere” representative of surface composition. In addition to atoms and molecules created in the mostly water ice surface such as H2O, O2, H2, the atmosphere is known to have species representative of trace surface materials. These trace species are carried off with the 10-104 H2O molecules ejected by each energetic heavy ion, a process we have simulated using molecular dynamics. Using the results of those simulations, we found that a neutral mass spectrometer orbiting ∼100 km above the surface could detect species with surface concentrations above ∼0.03%. We have also modeled the atmospheric spatial structure of the volatile species CO2 and SO2 under a variety of assumptions. Detections of these species with moderate time and space resolution would allow us to constrain surface composition, chemistry and to study space weathering processes. 相似文献
964.
We have investigated the role of group velocity in the calculation of pitch-angle diffusion coefficients by electron cyclotron harmonic (ECH) waves in planetary magnetospheres. The assumption which is generally made that the parallel group velocity can be neglected in comparison with particle parallel velocity is examined in detail. It is found that for lowest harmonic band this assumption is quite good. It is found that in general it is not possible to ignore the parallel group velocity. However, for lowest harmonic band this assumption is quite good at low electron temperatures. 相似文献
965.
966.
967.
968.
The magneto-rotational evolution of a neutron star in the massive binary system 4U 2206+54 is discussed in light of the recent
discovery of its 5555 s rotational period and its average rate of spin-down. We show that this behavior of the neutron star
means that its magnetic field exceeds the quantum mechanical critical limit and it is an accretion magnetar. The system’s
evolution is explained by wind driven mass transfer without formation of an accretion disk. The constant character of the
x-ray source indicates a steady rate of accretion and raises anew the question of the stability of the boundary of the magnetosphere
of a star undergoing spherical accretion. A solution to this problem is also a key to determining the mechanism for the slowing
down of the star’s rotation. 相似文献
969.
970.
Inspired by a recently observed axisymmetric field in a fully convective star we investigate the influence of an anisotropic diffusivity on the dynamo. We find that with reasonable assumptions for the anisotropy of the diffusivity and the α -effect the preference of axisymmetric modes is achieved. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献