A Fine Drizzle on Titan

by Paul Gilster on July 28, 2006

The current issue of Nature features a look at Huygens data with a big payoff: rain is falling on Titan, continues to fall as we speak, and will probably keep falling for a long time. Says Christopher McKay (NASA Ames), a co-author of the paper, “The rain on Titan is just a slight drizzle, but it rains all the time, day in, day out. It makes the ground wet and muddy with liquid methane. This is why the Huygens probe landed with a splat. It landed in methane mud.” All this from low, methane-nitrogen clouds that are barely visible but appear to be widespread, affecting weather globally. A Nature feature on this work, from which the McKay quote is drawn, can be found here.

Methane rains are what you get at temperatures of minus 179 degrees Celsius, as are the river-like features also found by the probe as it descended on January 14, 2005. The latter surely derive from the ceaseless rains as well. McKay says the rain equals roughly two inches a year, about as much as Death Valley gets on Earth, but on Titan the rain falls all year round. All this at the same time that Cassini’s radar images have shown lakes in Titan’s northern hemisphere. We’re talking bodies of water as large as North America’s Great Lakes.

Interestingly, drizzle alone can’t account for the geological features thus far observed on Titan, indicating more substantial rainstorms at other times. And another letter to the same issue of Nature by Ricardo Hueso and Agustín Sánchez-Lavega (University of the Basque Country, Bilbao, Spain) discusses their simulations of Titan’s methane clouds, which found a substantial likelihood of bouts of heavy rainfall during what they depict as severe convective storms.

Huygens landing site

Image: This image provides a comparison between the Huygens landing site on Titan as viewed by the Cassini Imaging Science Subsystem (ISS) and the NACO/SDI instrument mounted on the 8-metre Yepun telescope of the VLT (Very Large Telescope) station, in Chile. Credit: NASA/JPL/Cassini-ISS/Space Science Institute and ESO/NACO-SDI/VLT.

Be aware as well of an extensive series of papers on ground-based observations during the Huygens descent and landing including Witasse, Lebreton et al., “Overview of the coordinated ground-based observations of Titan during the Huygens mission,” in the Journal of Geophysical Research (July 27, 2006). The Titan landing was one of the largest ground-based observational campaigns ever undertaken in support of a space mission.

From an ESA news release on the effort:

The radio experiments worked beyond expectations and even proved to be a ‘safety net’ when the reception of Huygens’ second communications channel failed during the descent. The data from several of Huygens’ six experiments was lost, including that required for the Huygens radio experiment to track the winds during the whole descent. The Doppler-tracking data from the Green Bank Telescope (West Virginia, America) and from Parkes (Australia) provided real-time information about the probe’s drift in the winds. The processing of the VLBI data set is not yet completed but initial results look very promising.

The Very Long Baseline Interferometry (VLBI) observations, which included the use of 17 telescopes, should provide a second window on the Huygens’ landing. We already have an exact fix on Huygens touchdown (10.33 degrees south and 192.32 degrees west) from a combination of Cassini and Huygens data. VLBI data will provide an independent reconstruction of the descent sequence.

John Latter July 29, 2006 at 0:34

There’s a related news item at Methane makers yield to science which says:

The genetic code of an important group of methane-producing microbes has been sequenced by German scientists.

The archaea are probably the major source of methane emanating from rice fields, contributing up to a quarter of global emissions of the gas.

The article goes on to say that an archaea group called Rice Cluster I (RC-I) is probably responsible and then ends:

Some researchers hold out hope that some of the methane traces observed on Mars, for example, may be coming from organisms like RC-I.

John Latter / Jorolat
(Evolution Research)

Dagon July 29, 2006 at 7:23

Imagine a colony there, a series of antarctic style cylinders, a small reactor for energy, and on the lower levels of what looks like a small oil rig platform a 3 meter large blister cupola observation window, some 3 meters above the ground level. 4 layers of transparant glass, insulated, looking out of a shallow lake, unchanging over months. Imagine a scientist there, sipping coffee, reading a printout, greenblue glare of monitors, as a greasy rain hisses as it strikes the window (which is hot for titan standards). Imagine that landscape, staring at it, dimly lit in the eerie sunlight, cloud decks slowly sliding by, ice the color of yellowish brown sludge illuminated by the station’s warning lights.

We as humans could do it, actually go there. Before the end of this century.

pfdietz July 29, 2006 at 10:08

How plausible is life in which liquid hydrocarbons, such as methane, ethane, etc., substitute for water? The problem I see would be the low solubility of many compounds at those low temperatures, but perhaps there’s enough variety in the molecules that are soluble to make something work.

larry July 29, 2006 at 11:19

So would any of these conditions allow lighting? Thunder storms?

Charlie (Colorado) July 29, 2006 at 16:08

A quibble, but …

We’re talking bodies of water as large as North America’s Great Lakes.

Betcha we’re not. Not bodies of water anyway. Methane and ethane I’d believe.

Adam Crowl July 30, 2006 at 20:22

Hi All

The Antarctic style base is a good idea – or even the new mobile base that one European country has recently developed might be a good idea.

One thought that might help base building is the idea that recent impact craters should have large lenses of liquid water – this would provide useful ‘cryothermal’ energy, at least for warming the base above the surface ambient temperatures.

Another image that struck me was the possibility of ‘open air’ docks – not oxygenated, but warm enough for people to work without cryosuits, just wearing an oxygen mask. There’s nothing in the atmosphere sufficiently reactive at say 200 K to pose any danger and people in Siberia frequently live and work in 200 K air temperatures. I saw a cryochamber on a TV science magazine show the other day in which the walls were 120 K, but the air was still tolerable for brief exposures. It wouldn’t be open to the sky, but more like the open dock on Hoth in “The Empire Strikes Back”. Perhaps a series of downward blowing ‘airwalls’ would provide enough of a transition between the inner and outer environments?

Adam

Mike December 5, 2007 at 12:26

It all sounds exciting but imagine the smell. It’s like spending the day in a cow pasture during a light rain. mmmmm

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