论文标题
Ganymede表面组成的全局建模：VLT/Sphere的近IR映射
Global Modelling of Ganymede's Surface Composition: Near-IR Mapping from VLT/SPHERE
论文作者
论文摘要
我们介绍了Ganymede的表面组成的地图，几乎完整的经度覆盖范围，使用高空间分辨率近红外（0.95至1.65 $μm$）从地面VLT/SPHERE仪器中获得。使用马尔可夫链蒙特卡洛法对观察到的反射光谱进行建模，以估计水冰，酸，盐和光谱浅瓦的黑暗剂的丰富性和相关的不确定性。结果证实，在年轻的明亮地形（冲击火山口，沟）和较低的黑暗地形（例如伽利略·雷吉奥）的年轻明亮地形（撞击者，沟）和低α频谱材料中，ganymede的表面由水冰支配。冰粒尺寸具有较强的纬度和纵向梯度，在赤道和后半球上具有较大的谷物。这些趋势与纬度热梯度和辐射驱动溅射的全局变化的影响一致。硫酸的丰度较低，并且似乎与血浆轰击相关，在该血浆轰击中，甘氏杆菌的杆暴露于外部Jovian磁场。最佳估计的丰度表明可能存在盐的混合物，尽管它们的丰度，光谱变性和相关的不确定性意味着无法自信地检测到个别盐。如果存在的话，硫酸钠和氯酸镁似乎与外源性等离子体轰击暂时相关，而氯化镁和硫酸镁似乎与年轻的地形暂时相关，这意味着可能的内源性起源。 MCMC建模还在伽利略/NIMS数据上进行，显示了可比的分布。球体的高空间分辨率允许对小尺度（<150公里）的表面特征进行精确的映射，可以与较高的光谱分辨率观察一起使用，以共同确认潜在物种的存在和分布。
We present maps of Ganymede's surface composition with almost complete longitude coverage, acquired using high spatial resolution near-infrared (0.95 to 1.65$μm$) observations from the ground-based VLT/SPHERE instrument. Observed reflectance spectra were modelled using a Markov Chain Monte Carlo method to estimate abundances and associated uncertainties of water ices, acids, salts and a spectrally-flat darkening agent. Results confirm Ganymede's surface is dominated by water ice in young bright terrain (impact craters, sulci), and low-albedo spectrally-flat material in older dark terrain (e.g. Galileo Regio). Ice grain size has strong latitudinal and longitudinal gradients, with larger grains at the equator and on the trailing hemisphere. These trends are consistent with the effects of the latitudinal thermal gradient and global variations in radiation driven sputtering. Sulphuric acid has a low abundance and appears potentially spatially correlated with plasma bombardment, where Ganymede's poles are exposed to the external jovian magnetic field. Best-estimate abundances suggest a mixture of salts could be present, although their low abundances, spectral degeneracies and associated uncertainties mean individual salt species cannot be detected with confidence. If present, sodium magnesium sulphate and magnesium chlorate appear tentatively correlated with exogenic plasma bombardment, while magnesium chloride and sulphate appear tentatively correlated with younger terrain, implying a possible endogenic origin. MCMC modelling was also performed on Galileo/NIMS data, showing comparable distributions. The high spatial resolution of SPHERE allows the precise mapping of small scale (<150km) surface features, which could be used along with higher spectral resolution observations to jointly confirm the presence and distribution of potential species.
