Hall D T, Strobel D F, Feldman P D, McGrath M A, Weaver H A
Center for Astrophysical Sciences, Johns Hopkins University, Baltimore, Maryland 21218.
Nature. 1995 Feb 23;373(6516):677-81. doi: 10.1038/373677a0.
Europa, the second large satellite out from Jupiter, is roughly the size of Earth's Moon, but unlike the Moon, it has water ice on its surface. There have been suggestions that an oxygen atmosphere should accumulate around such a body, through reactions which break up the water molecules and form molecular hydrogen and oxygen. The lighter H2 molecules would escape from Europa relatively easily, leaving behind an atmosphere rich in oxygen. Here we report the detection of atomic oxygen emission from Europa, which we interpret as being produced by the simultaneous dissociation and excitation of atmospheric O2 by electrons from Jupiter's magnetosphere. Europa's molecular oxygen atmosphere is very tenuous, with a surface pressure about 10(-11) that of the Earth's atmosphere at sea level.
木卫二是距离木星第二远的大型卫星，大小与地球的月球大致相同，但与月球不同的是，它的表面有冰。有人提出，在这样一个天体周围应该会积累起一层氧气大气层，这是通过分解水分子并形成分子氢和氧的反应实现的。较轻的氢分子会相对容易地从木卫二逃逸，留下富含氧气的大气层。在此我们报告对木卫二原子氧发射的探测，我们将其解释为由木星磁层中的电子使大气中的氧气分子同时解离和激发而产生的。木卫二的分子氧大气层非常稀薄，其表面压力约为地球海平面大气压力的10的负11次方。
