Possible tropical lakes on Titan from observations of dark terrain

摘要

土星卫星“土卫六”有一个“甲烷循环”，它在rn原理上与地球上的水循环是相似的，尽管“土rn卫六”上的表面液体似乎相对很少，主要是在rn高纬度处被检测到。“土卫六”能够给其大气rn层供应甲烷的事实，再加上在Huygens探测器rn着陆点周围(该着陆点像是在一个热带干早地rn区)存在表面水侵蚀的迹象，表明可能有更多rn表面液体有待发现。这篇论文报告了热带一个rn区域的近红外光谱图像，这些图像显示存在一rn个暗的区域，这可能表示该卫星表面存在液态rn甲烷，甲烷的来源则在地表下。%Titan has clouds, rain and lakes-like Earth-but composed of methane rather than water. Unlike Earth, most of the condensable methane (the equivalent of 5 m depth globally averaged) lies in the atmosphere. Liquid detected on the surface (about 2 m deep) has been found by radar images only poleward of 50° latitude, while dune fields pervade the tropics. General circulation models explain this dichotomy, predicting that methane efficiently migrates to the poles from these lower latitudes. Here we report an analysis of near-infrared spectral images of the region between 20° N and 20° S latitude. The data reveal that the lowest fluxes in seven wavelength bands that probe Titan's surface occur in an oval region of about 60 × 40 km~2, which has been observed repeatedly since 2004. Radiative transfer analyses demonstrate that the resulting spectrum is consistent with a black surface, indicative of liquid methane on the surface. Enduring low-latitude lakes are best explained as supplied by subterranean sources (within the last 10,000 years), which may be responsible for Titan's methane, the continual photochemical depletion of which furnishes Titan's organic chemistry.