Surface temperature lowering at Bright Ephemeral Feature site on Titan’s north pole

We report a temperature decrease in one of the regions on Titan that has been documented as a Bright Ephemeral Feature (BEF). Spectra were recorded by the Composite Infrared Spectrometer (CIRS) on Cassini. BEFs are 5µm bright areas that appear, disappear, and shift from flyby to flyby at Titan’s north pole observed in Visual and Infrared Mapping Spectrometer (VIMS) data. They are inferred to be broad-specular reflections caused by a smooth surface on Titan or a near surface fog —both of which indicate that the atmosphere interacted with the surface. We used 24 spectra for ‘on the spot’ and 51 spectra for ‘off the spot’ (where spot is the BEF region) to determine the temperature difference during the T121 flyby (July 25 2016). At the 410-560 cm−1 window where surface emissions are perceptible we see a decrease in temperature by 1±0.1 Kelvin. This lowering of temperature might indicate precipitative cooling after a fresh rainfall on Titan’s land/sea surface.

本研究报道了土卫六（Titan）一处被记录为短暂亮斑（Bright Ephemeral Feature，BEF）的区域内的温度下降现象。相关光谱由卡西尼号搭载的复合红外光谱仪（Composite Infrared Spectrometer，CIRS）采集得到。BEF为5微米波段的亮区，在土卫六北极区域的可见与红外绘图光谱仪（Visual and Infrared Mapping Spectrometer，VIMS）观测数据中，这类亮区会随飞掠任务交替出现、消失并发生位置偏移。研究推测此类亮区由土卫六表面光滑层或近地表雾团引发的宽幅镜面反射所致，这两种情况均表明土卫六大气与地表存在相互作用。本研究选取24份“原位”光谱与51份“异位”光谱（其中“位点”指BEF区域），针对2016年7月25日的T121飞掠任务开展温差分析。在可观测到地表辐射的410~560 cm⁻¹光谱窗口内，我们测得温度下降了1±0.1开尔文。该温度下降现象或表明土卫六陆地/海洋表面经历了新一轮降雨后的降水冷却过程。