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首页> 外文期刊>Planetary and space science >New constraints on Ganymede's hydrogen corona: Analysis of Lyman-alpha emissions observed by HST/STIS between 1998 and 2014
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New constraints on Ganymede's hydrogen corona: Analysis of Lyman-alpha emissions observed by HST/STIS between 1998 and 2014

机译：对木卫三氢电晕的新限制：HST / STIS在1998年至2014年间观察到的Lyman-alpha排放分析

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Far-ultraviolet observations of Ganymede's atmospheric emissions were obtained with the Space Telescope Imaging Spectrograph (STIS) onboard of the Hubble Space Telescope (HST) on several occasions between 1998 and 2014. We analyze the Lyman-alpha emission from four HST campaigns in order to constrain the abundance and variation of atomic hydrogen in Ganymede's atmosphere. We apply a forward model that estimates surface reflection and resonant scattering in an escaping corona of the solar Lyman-alpha flux, taking into account the effects of the hydrogen in the interplanetary medium. The atmospheric emissions around Ganymede's disk derived for the observations taken between 1998 and 2011 are consistent with a hydrogen corona in the density range of (5-8) x 10(3) cm(-3) at the surface. The hydrogen density appears to be generally stable in that period. In 2014, Ganymede's corona brightness is approximately 3 times lower during two observations of Ganymede's trailing hemisphere and hardly detectable at all during two observations of the leading hemisphere. We also investigate extinction of Ganymede's coronal emissions in the Earth's upper atmosphere or geocorona. For small Doppler shifts, resonant scattering in the geocorona of the moon corona emissions can effectively reduce the brightness observed by HST. In the case of the 2014 leading hemisphere observations, an estimated extinction of 80% might explain the non-detection of Ganymede's hydrogen corona. Geocoronal extinction might also explain a previously detected hemispheric difference from Callisto's hydrogen corona.
机译：在1998年至2014年之间，多次使用哈勃太空望远镜（HST）上的太空望远镜成像光谱仪（STIS）对木卫三的大气排放进行了远紫外观测。我们分析了来自四个HST活动的Lyman-alpha排放，限制木卫三大气中氢原子的丰度和变化。考虑到氢在行星际介质中的影响，我们应用了一个前向模型，该模型估算了逃逸的太阳Lyman-α通量电晕中的表面反射和共振散射。根据1998年至2011年之间进行的观测得出的Ganymede圆盘周围的大气排放与表面上（5-8）x 10（3）cm（-3）密度范围内的氢电晕一致。在此期间，氢密度似乎总体上是稳定的。 2014年，在两次对木卫三尾随半球的观测中，木卫三的日冕亮度降低了约3倍，而在对前半球的两次观测中则几乎无法检测到。我们还研究了地球高层大气或日冕中木卫三日冕辐射的消灭。对于小的多普勒频移，月球电晕发射中的地球电晕中的共振散射可以有效降低HST观测到的亮度。在2014年领先的半球观测中，估计已灭绝80％，这可能解释了未检测到木卫三氢电晕的原因。冠冕的灭绝也可以解释先前发现的与卡利斯托氢电晕的半球差异。

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