The temporal variability 1 of Io’s hotspots

We investigate the variability of the power emission of Io’s hotspot by using recent Juno/JIRAM infrared observations. The Jovian Infrared Auroral Mapper (JIRAM) is an imaging spectrometer which began observing Jupiter in August 2016. Although observing Jupiter’s moons is not its primary objective, JIRAM can use the frequent opportunities to observe Io (up to once per orbit) to gather infrared images and spectra of its surface. The present study uses the data acquired by JIRAM during the last two years, including the location and morphology of Io’s hotspots, and the temporal variability of the total output. A new photometric model for the hotspots and the dayside surface has been developed, which permits to disentangle the temporal variability from the changes in the observation geometry. While the latitudinal dependence of the power output is not well constrained, low-latitude hotspots show a significantly more intense temporal variability and larger temperature.

本研究借助近期朱诺号（Juno）/木星红外极光绘图仪（JIRAM，Jovian Infrared Auroral Mapper）的红外观测数据，探究木卫一（Io）热点的功率辐射变化规律。木星红外极光绘图仪（JIRAM）作为一款成像光谱仪，于2016年8月正式开启木星观测工作。尽管观测木星卫星并非其核心观测目标，但JIRAM可依托每个轨道最多一次的木卫一观测窗口，获取其表面的红外图像与光谱数据。本研究所用数据来自JIRAM近两年来的观测结果，涵盖木卫一热点的位置、形态特征，以及总辐射功率的时间变化特性。研究团队开发了一套针对热点与昼侧表面的全新光度模型，能够将观测几何变化带来的影响与时间演化特征分离开来。尽管目前尚未对功率输出的纬度依赖性形成有效约束，但低纬度热点展现出显著更强的时间变化性与更高的温度。