GC–MS Analysis on Titan Mission

The European-built Huygens probe made history on January 14 by becoming the first spacecraft to land on Saturn’s largest moon. The Huygens gas chromatography–mass spectrometry team concluded that methane rain occurs on the moon, and GC–MS can distinguish between two isotopic forms of carbon — carbon-12 and carbon-13. By comparing the carbon-12/13 ratios it might be possible to pin a biological source to the methane arising from the interior of Titan.
May 02, 2005

The Discoveries so Far Although it will take months for the science team to officially release their scientific papers and possibly many more years to analyze fully all the Huygens data, some of the early information already is telling us much about this strange world. The Descent Imager provided pictures of a hazy world with 350-ft high ridges of water ice surrounded by hills with river-channels running down to smooth dark plains of dry hydrocarbons (Figure 3). The Huygens GC–MS team concluded that methane rain occasionally drenches the hills thus washing ice and hydrocarbons down into the smooth dark plains areas seen in the images where they collect and dry out. Considering that the light at the surface of Titan is only 1% of the illumination of a sunlit Earth and the fact the Huygens DISR camera worked as well as it did was simply astonishing. Add to this that the data stream from the Huygens probe on the surface of Titan continued on for 70 min — far beyond the expected time of only 3 min.

The deceleration and penetration data from the Surface Science Package indicated that the probe had slightly sank in the soft surface material about 6 in., revealing a surface texture of analogous to wet sand mixed with ice. However, as the heat from the warm probe melted the soil–ice mixture under the lander the GC–MS and SSP spectrometers detected methane being released as a gas indicating that the methane was originating from below Titan's surface — an early major scientific finding.

Surface imagery at the landing site further revealed pebbles and small rocks strewn about. Infrared spectra obtained from the DISR camera showed these were consistent with the composition of rock hard water ice. Figure 4 shows a color view of from the surface of Titan after processing to add reflection spectra data. Pebbles initially thought to be rocks or ice blocks appear strewn about near the Huygens lander. The two rock-like objects just below the middle of the image are about 6-in. high (left) and about 1.5-in. (center) across respectively, at a distance of about 33 in. from Huygens. The surface is darker than originally expected, consisting of a mixture of water and hydrocarbon ice. There also is evidence of erosion at the base of these objects, indicating possible fluvial activity.

Another major finding by the Huygens GC–MS system was the detection of argon-40 arising from the decay of potassium-40 indicating to the science team that Titan does experience volcanic activity but unlike Earth where basaltic lava is the prime ingredient, Titan instead releases water ice and ammonia. This means that outgassing from Titan's interior is an ongoing process.

Chances of Life On Titan? Although the surface temperatures on Titan would not allow for the survival of any known microbial life, astrobiologists have pondered the source of the methane. It is well know that without a source of constant replenishment of methane, Titan would have lost this gas in about 10,000 years. The GC–MS system on Huygens has indicated that methane is emanating from the interior of Titan, so is it possible that microbial life exists deep inside the moon? Some models of Titan's interior suggest there is an ocean of methane 62 miles deep about 200 miles below the surface. If true could methanogenic bacteria be producing the gas? While the Huygens team remains extremely skeptical about this, the GC–MS system does have the capability to distinguish two isotopic forms of carbon — carbon-12 and carbon-13. Methanogenic bacteria as well as all other known life forms on our planet incorporate carbon-12 while carbon-13 is not. By comparing the carbon-12/carbon-13 ratios it might be possible to pin a biological source to the methane arising from the interior of Titan. One thing is sure: the data returned from the Huygens probe will be studied for years to come.

Barry E. DiGregorio is an astrobiologist for the Cardiff Centre for Astrobiology in Wales, UK.

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