Morning mist decends on Titan

“Persistent drizzle moving in from the coast clearing late morning” – a phrase frequently used in weather forecasts across the world can now be applied to the weather on Saturn’s largest moon, Titan, according to new research.

Artist’s impression of space probe Huygens landing on Titan (Credit: ESA)

The near infrared observations made by astronomers from the University of California, Berkeley using the European Southern Observatory’s (ESO) Very Large Telescope (VLT) in Chile for the first time the presence of a high altitude - near global - cloud that causes a widespread and persistent morning drizzle of methane over the western foothills of the main continent on Titan.

Team member Imke de Pater said: “Titan’s topography could be causing this drizzle. The rain could be caused by processes similar to those on Earth - moisture laden clouds pushed upslope by winds condense to form a coastal rain.”
Astronomers think that Titan, whose thick atmosphere is comprised mainly of nitrogen, resembles the early atmosphere of Earth. Previous observations have shown that the entire moon is swathed in a hydrocarbon haze extending as high as 500km, becoming thinner with height.

Due to the extremely cold surface temperatures on Titan (minus 183ËšC), trace chemicals such as methane and ethane exist as solids and liquids on Titan. Surface features near the poles are thought to be lakes of liquid hydrocarbon, analogous to oceans on Earth, presumably filled by methane precipitation. This new result is the first observation of rain falling onto the surface.

One difference between the drizzle on Titan and Earth is the size of the droplets. On Titan the methane droplets are predicted to be at least millimeter sized, a thousand times larger than in terrestrial clouds.