Astrospheric shielding of habitable planets

一颗位于宜居地带的系外行星的大气层顶部受到银河系连环流和中性氢原子流的撞击。这些通量可以改变大气的组成，因此也可能改变生物特征，如臭氧或甲烷。银河系宇宙射线的流量以及来自星际介质的中性氢原子的流量都受到天体的强烈影响。天体球体是超快磁声恒星风膨胀的区域，最终在星际介质的边界处形成激波结构。因为恒星风和星际介质都有磁场，所以需要对天体球体进行3D模拟。此外，由于漫射张量依赖于所有三个空间维度，因此需要用3D模拟来模拟漫画光线的调制。在本项目中，将模拟天体的3D结构。天体的对称性取决于星际磁场的方向，星际磁场将以45度的步长变化，以确定星际磁场方向的影响。此外，还将对不同的恒星进行建模，这些恒星在宜居带中有系外行星，具有不同的风和星际环境。根据该模型，中性氢的通量可以在行星的位置直接确定，而宇宙射线的通量将由E.Engelbrecht的3D传输代码使用3D Astroball模型来模拟。该项目的目标是确定行星外大气顶部的宇宙线和中性氢通量，并找到一个简单的公式来描述这些通量。

The top of the atmosphere of an exo-planet in a habitable zone is hit by a galactic comic flux as well as a flux of neutral hydrogenatoms. These fluxes can change the composition of the atmosphere and therefore also possible bio signatures, like ozone or methane. The flux of the galactic cosmic rays as well as that of the neutral hydrogen atoms from the interstellar medium is strongly influenced by an astrosphere. The astrosphere is the region, in which the super fast-magnetsonic stellar wind expands and finally at the boundary to the interstellar medium a shock structure is created. Because the stellar wind as well as the interstellar medium have a magnetic field, a 3D simulation of the astrosphere is required. Also the modulation of the comic rays needs to be modeled with a 3D simulation, because the diffusion tensor depends on all three space dimensions.In this project the 3D structure of the astrosphere shall be modeled. The symmetry of the astrosphere depends on the orientation ofthe interstellar magnetic field, which will be varied in 45 degree steps to determine the influence of the orientation of the interstellar magnetic field. In addition different stars, which have exo-planets in the habitable zone, with different winds and interstellar environments will be modeled. From that models the flux of the neutral hydrogen can be determined directly at the position of the planet, while the cosmic ray flux will modeled with a 3D transport code by E. Engelbrecht using the 3D astrosphere models.The goal of the project is to determine the cosmic ray and neutral hydrogen flux at the top of an exo-planetary atmosphere and to find asimple formula to describe these fluxes.