Evidence for layered methane clouds in Titan’s troposphere

Layered methane clouds in Titan’s troposphere with an upper methane ice cloud, a lower liquid methane–nitrogen cloud, and a gap in between were suggested from in situ measurements and ground-based observations. Here we report laboratory investigations under conditions that mimic Titan’s troposphere providing a detailed picture of the cloud layers. A solid methane cloud with a nitrogen content of less than 14% and a liquid methane–nitrogen cloud with a nitrogen content of 30% form above 19 km and below 16 km altitude, respectively. Contrary to previous assertions, long-lived supercooled liquid methane–nitrogen droplets can be sustained in the region in between. The results demonstrate that a cloud gap could only form in the presence of high amounts of other traces species (ethane nuclei, tholin particles, etc.). 2009 Elsevier Inc. All rights reserved.