Methane Gas Stabilizes Supercooled Ethane Droplets in Titan's Clouds

Abstract

Strong evidence for ethane clouds in various regions of Titan's atmosphere has recently been found. Ethane is usually assumed to exist as ice particles in these clouds, although the possible role of liquid and supercooled liquid ethane droplets has been recognized. Here, we report on infrared spectroscopic measurements of ethane aerosols performed in the laboratory under conditions mimicking Titan's lower atmosphere. The results clearly show that liquid ethane droplets are significantly stabilized by methane gas which is ubiquitous in Titan's nitrogen atmospherea phenomenon that does not have a counterpart for water droplets in Earth's atmosphere. Our data imply that supercooled ethane droplets are much more abundant in Titan's clouds than previously anticipated. Possibly, these liquid droplets are even more important for cloud processes and the formation of lakes than ethane ice particles.

The composition of liquid methane–nitrogen aerosols in Titan’s lower atmosphere from Monte Carlo simulations

“…With the viability of the approach in principle established by the present study it should be possible to investigate the fate of ethane in Titan's atmosphere, which is assumed to be a major constituent of polar ethane clouds and of lakes on the moon's surface (Griffith et al, 2006;Cordier et al, 2009). Contrary to current assumptions, recent aerosol experiments from our laboratory show that especially in mixtures with methane and possibly nitrogen, ethane could very well stay liquid throughout most of the atmosphere (Wang et al, 2010b; Lang, E.K., Knox, K.J., Wang, C.C., Signorell, R., 2010, submitted for publication). Due to the lack of experimental data at low temperatures, phenomenological thermodynamic models are less reliable to predict the phase equilibrium of mixtures containing ethane.…”

On the formation of polyacetylenes and cyanopolyacetylenes in Titan's atmosphere and their role in astrobiology

“…11 This leads to latitudinal and seasonal patterns of hydrocarbons in the atmosphere of Titan, which might provide nucleation sites for hydrocarbon snow and rain. [12][13][14] Therefore, an understanding of the formation of the haze layers is also important to rationalize Titan's meteorology. 15,16 However, the basic chemical processes, which initiate and control the formation of these haze layers, have been the least understood to date, 17 and none of Titan's photochemical models [18][19][20][21][22] has been able to reproduce the atmospheric molecular mixing ratios obtained from the Cassini-Huygens observations.…”

Low-temperature Bessel beam trap for single submicrometer aerosol particle studies

“…Finally, the experimental temperature range of our current apparatus is limited and spans a range from approximately room temperature (300 K) to 223 K. We would like to extend this from 373 K to as low as 78 K to study single pure and mixedcomponent particles that may be relevant to planetary and lunar atmospheres to complement our previous studies of particle ensembles. [48][49][50][51][68][69][70] Combining the more stable QBB trap and more accurate size determination with white light scattering in an apparatus that has a greater temperature range will provide the tools necessary for these future studies.…”

“…We show first examples of homogeneous and heterogeneous freezing, freezingmelting cycles, and evaporation of single particles. In the following work, we explore single, submicrometer-sized water and hydrocarbon aerosols that are stably trapped on the order of hours in a CPBB trap across a wide temperature range (226-330 K) relevant to planetary and lunar atmospheres (e.g., Earth, [44][45][46][47] Mars, 48 Titan [49][50][51] ). Studying finemode (r < 1 μm) water and hydrocarbon aerosols at cold temperatures may help us to better understand, respectively, cirrus clouds that form in the upper troposphere/lower stratosphere, as well as organic aerosols in the lower troposphere with anthropogenic origins.…”