Seki K, Elphic R C, Hirahara M, Terasawa T, Mukai T
Department of Earth and Planetary Sciences, University of Tokyo, Hongo 7-3-1, Bunkyo, Tokyo 113-0033, Japan.
Science. 2001 Mar 9;291(5510):1939-41. doi: 10.1126/science.1058913.
In Earth's environment, the observed polar outflow rate for O(+) ions, the main source of oxygen above gravitational escape energy, corresponds to the loss of approximately 18% of the present-day atmospheric oxygen over 3 billion years. However, part of this apparent loss can actually be returned to the atmosphere. Examining loss rates of four escape routes with high-altitude spacecraft observations, we show that the total oxygen loss rate inferred from current knowledge is about one order of magnitude smaller than the polar O(+) outflow rate. This disagreement suggests that there may be a substantial return flux from the magnetosphere to the low-latitude ionosphere. Then the net oxygen loss over 3 billion years drops to approximately 2% of the current atmospheric oxygen content.
在地球环境中，观测到的O(+)离子的极地流出率是高于引力逃逸能量的氧气的主要来源，这相当于在30亿年的时间里，现今大气中约18%的氧气流失。然而，这种明显的流失中有一部分实际上可以返回大气层。通过高空航天器观测来研究四条逃逸路径的流失率，我们发现，根据现有知识推断出的总氧流失率比极地O(+)流出率小约一个数量级。这种差异表明，可能存在从磁层到低纬度电离层的大量返回通量。这样一来，30亿年间的净氧流失量降至当前大气氧含量的约2%。
