Fragments of the parent molecules recombine and form more complex compounds. Photochemical models predict that ethane should be the main organic product of these atmospheric reactions.
If ethane and other complex organics rain down from the atmosphere onto Titan's surface, we would expect to find huge seas of ethane there. In fact, until recently it was believed that the surface of Titan was mainly composed of lakes or oceans of liquid hydrocarbons, with dry "islands" also covered with complex organic deposits.
Stirring the pot
While ground-based telescopes have confirmed earlier observations made by the Hubble Space Telescope (HST), tantalizing new results at infrared wavelengths have stirred up the debate about what the surface of Titan is really like.
In particular, excellent observing conditions during a recent observation campaign with the new adaptive optics system -- PUEO -- at the Canada-France-Hawaii Telescope (CFHT) produced images of excellent quality.
The images were taken in the middle of the "methane window" wavelengths at 1.3 micrometers and 1.6 micrometers.
Methane, like other substances, absorbs incoming light photons to varying degrees depending on the particle's wavelength. This allows us to "see" Titan's surface through these so-called methane windows.
The results were discussed at the General Assembly of the European Geophysical Society (EGS) in Nice in March 2001.
"We have been obtaining data with adaptive optics since 1994" says Athena Coustenis, an astronomer at the Paris-Meudon Observatory and one of the scientists involved in both the ADONIS (ESO) and HST observation campaigns. "When both ADONIS at ESO in Chile and HST produced an acceptable image of Titan, it was the first to show Titan's surface."
The bright spot of Titan
These observations showed the existence of a bright area, especially in the high-contrast ADONIS images, but it took the PUEO campaign to make it possible to analyze the details of this spot at shorter wavelengths.
"Having a good instrument is not enough, it is also important to have good weather, even in Mauna Kea," said Coustenis. "Recently, we were lucky and we obtained diffraction-limited images. In addition, another bright feature at Titan's western limb was noticed for the first time. This feature might be diagnostic of diurnal (daily) effects but requires further investigation before its origin can be firmly identified."
The researchers also obtained a map of Titan's geometrical albedo, or tendency to reflect light.
"From our albedo maps, it appears that the darker areas are about three times darker than the bright spot and they are compatible with a combination of organic deposits and ice extents, possibly related to topography," concluded Coustenis.
Another important feature of the recent CFHT observations was the acquisition of data at 0.9 micrometers (another methane window) with the spectrograph OASIS, which provides information for the first time at more than 70 different locations on Titan's disk.
advertisement
