宇宙线对外日球层结构的影响

2012年夏天,旅行者1号探测器成功地穿越太阳系边缘(日球层顶)并进入了星际空间。传统认为日球层顶是一个压力平衡结构,将内外日球层鞘区分隔开来。在日球层附近,太阳风的总压力,包含了pickup ions和异常宇宙线(Anomalous cosmic rays即ACRs)约等于星际介质和磁场压力的总和。如果其中某个压力突然改变的话,那么日球层会向内压缩或向外膨胀以补偿这种压力变化并达到新的平衡态。基于旅行者1号的观测,部分ACRs可能已经跨越日球层顶并逃逸进入星际介质,这样一个过程并没有被之前的日球层MHD模型所考虑。所以这里我们将评估ACR的逃逸对日球层结构的影响,采用的方法是在传统的MHD方程里引入宇宙线扩散方程，我们期待这样的一种处理方式能够解释已有的MHD模型预测日球层顶比实际观测要大的问题，并结合旅行者探测器对终止激波的探测数据，对宇宙线的作用提出新的思路。

A major Voyager discovery in deep space exploration was made in the summer of 2012, when the Voyager 1 space probe crossed the boundary of the solar system, known as the heliopause, and for the first time entered interstellar space. The heliopause is a pressure balanced structure that separates the inner and outer heliosheaths. The total pressure of the solar wind particles, including pickup ions and anomalous cosmic rays(ACRs), is approximately equal to the pressure of the interstellar gas and its magnetic field on the outer side. Should one of the pressure change, the heliosphere will shrink or expand in response, to compensate for the imbalance and reach a new equilibrium state. Based on Voyager 1 observations, some ACRs may have crossed the heliopause and escaped into the interstellar medium, providing a mechanism of energy transfer between the inner and outer heliosheaths that is not included in conventional MHD models. Here we evaluate the effect of ACR escape on the size and shape of the heliosphere using a simple model that includes the transport of cosmic rays across the heliopause. We show that this effect could be a possible explanation for the unexpectedly early heliopause encounter by Voyager 1.