Lakes of Titan

The lakes of Titan, a moon of Saturn, are bodies of liquid methane that have been detected by the "Cassini" space probe, and had been suspected long before. The large ones are known as maria (seas) and the small ones as laci (lakes). [http://planetarynames.wr.usgs.gov/jsp/FeatureTypes2.jsp?system=Saturn&body=Titan&systemID=6&bodyID=30&sort=AName&show=Fname&show=Lat&show=Long&show=Diam&show=Stat&show=Orig Titan] at the "USGS Gazetteer of Planetary Nomenclature", accessed April 12, 2008.]

The possibility that there were seas of liquid methane on Titan were first suggested based on Voyager 1 and 2 data that showed Titan to have a thick atmosphere of approximately the correct temperature and composition to support them, but direct evidence wasn't obtained until 1995 when data from Hubble and other observations had already suggested the existence of liquid methane on Titan, either in disconnected pockets or on the scale of satellite-wide oceans, similar to water on Earth. [cite journal| author= S. F.Dermott, C. Sagan, |year=1995| title= Tidal effects of disconnected hydrocarbon seas on Titan
journal=Nature |volume=374 | pages=238–240 |doi=10.1038/374238a0]

The "Cassini" mission affirmed the former hypothesis, although not immediately. When the probe arrived in the Saturnian system in 2004, it was hoped that hydrocarbon lakes or oceans might be detectable by reflected sunlight from the surface of any liquid bodies, but no specular reflections were initially observed. [cite web |first=Henry|last=Bortman|url= http://saturn.astrobio.net/news/article81.html|title=Titan: Where's the Wet Stuff? |accessdate=2007-08-28 |date=November 02, 2004 |publisher=Astrobiology Magazine]

The possibility remained that liquid ethane and methane might be found on Titan's poles, where it was expected to be abundant and stable. At Titan's south pole, an enigmatic dark feature named Ontario Lacus was the first suspected lake identified, possibly created by clouds that are observed to cluster in the area. [cite news| url=http://www.planetary.org/news/2005/0628_Dark_Spot_Near_the_South_Pole_A.html| title=Dark Spot Near the South Pole: A Candidate Lake on Titan?| publisher=The Planetary Society| |author=Emily Lakdawalla |date=June 28, 2005 |accessdate=2006-10-14] A possible shoreline was also identified at the pole via radar imagery. [cite press release| url=http://www.spaceref.com/news/viewpr.html?pid=17829| title=NASA Cassini Radar Images Show Dramatic Shoreline on Titan|date=September 16, 2005| accessdate=2006-10-14| publisher=Jet Propulsion Laboratory] Following a flyby on July 22, 2006, in which the "Cassini" spacecraft's radar imaged the northern latitudes (which are currently in winter), a number of large, smooth (and thus dark to radar) patches were seen dotting the surface near the pole.cite web| url=http://photojournal.jpl.nasa.gov/catalog/PIA08630| title=PIA08630: Lakes on Titan| publisher=NASA/JPL |work=NASA Planetary Photojournal | accessdate=2006-10-14] Based on the observations, scientists announced "definitive evidence of lakes filled with methane on Saturn's moon Titan" in January 2007.cite journal|title=The lakes of Titan|author=Stofan, E. R.|coauthors= Elachi, C.; et al.|issue=1 |volume=445|pages=61–64|journal=Nature|date=January 4, 2007|url=http://www.nature.com/nature/journal/v445/n7123/abs/nature05438.html|accessdate=2007-08-27|doi=10.1038/nature05438] [cite web |url=http://saturn.jpl.nasa.gov/news/features/feature20070103.cfm |title=Titan Has Liquid Lakes, Scientists Report in Nature |publisher=NASA/JPL |date=January 3, 2007 |accessdate=2007-01-08] The "Cassini–Huygens" team concluded that the imaged features are almost certainly the long-sought hydrocarbon lakes, the first stable bodies of surface liquid found off Earth. Some appear to have channels associated with liquid and lie in topographical depressions.

Repeated coverage of these areas should prove whether they are truly liquid, as any changes that correspond with wind blowing on the surface of the liquid would alter the roughness of the surface and be visible in the radar. The high relative humidity of methane in Titan’s lower atmosphere could be maintained by evaporation from lakes covering only 0.002–0.02% of the whole surface.cite journal| author=Giuseppe, Mitri; "et al." |month=February|year=2007| title=Hydrocarbon Lakes on Titan |journal=Icarus |volume=186 | pages=385–394 |doi=10.1016/j.icarus.2006.09.004 |url=http://www.lpl.arizona.edu/~showman/publications/mitri-etal-2007-lakes.pdf |format=PDF]

During a "Cassini" flyby in late February 2007, radar and camera observations revealed several large features in the north polar region that may be large expanses of liquid methane and/or ethane, including one sea with an area of over 100,000 km² (larger than Lake Superior), and another (though less definite) region potentially the size of the Caspian Sea. [cite news| url=http://www.nasa.gov/mission_pages/cassini/media/cassini-20070313.html| title=Cassini Spacecraft Images Seas on Saturn's Moon Titan| date=2007-03-13| accessdate=2007-03-14| publisher=NASA] A flyby of Titan's southern polar regions in October 2007 revealed similar, though far smaller, lakelike features. [cite web|title=News flash: Lakes at Titan's south pole, too, on top of the land of lakes in the north|author=Emily Lakdawalla|year=2007|work=The Planetary Society|url=http://www.planetary.org/blog/article/00001189/|accessdate=2007-10-12]

During a close Cassini flyby in December 2007 the visual and mapping instrument observed a lake, Ontario Lacus, in Titan's south polar region. This instrument identifies chemically different materials based on the way they absorb and reflect infrared light. Based on this instrument's observations, scientists concluded that at least one of the large lakes observed on Saturn's moon Titan does in fact contain liquid, that liquid being hydrocarbons, and have positively identified the presence of ethane. This makes Titan the only other object than Earth in the solar system known to have liquid on its surface. [http://www.jpl.nasa.gov/news/news.cfm?release=2008-152] This would make Titan a very interesting place to observe and study , to refine weather science, as differing liquid and gaseous materials and temperatures are at play there. This would help refine the science of Earth weather forecasting, allowing for better weather forecasts.

The discoveries at the poles contrast with the findings of the "Huygens" probe, which landed near Titan's equator on January 14 2005. The images taken by the probe during its descent showed no open areas of liquid, but strongly indicated the presence of liquids in the recent past, showing pale hills crisscrossed with dark drainage channels that lead into a wide, flat, darker region. It was initially thought that the dark region might be a lake of a fluid or at least tar-like substance, but it is now clear that "Huygens" landed on the dark region, and that it is solid without any indication of liquids. A penetrometer studied the composition of the surface as the craft impacted it, and it was initially reported that the surface was similar to wet clay, or perhaps crème brûlée (that is, a hard crust covering a sticky material). Subsequent analysis of the data suggests that this reading was likely caused by "Huygens" displacing a large pebble as it landed, and that the surface is better described as a "sand" made of ice grains. [cite news |url=http://news.bbc.co.uk/1/hi/sci/tech/4417503.stm |title=Titan probe's pebble 'bash-down' |publisher=BBC News |date=April 10 2005 |accessdate=2007-08-06] The images taken after the probe's landing show a flat plain covered in pebbles. The pebbles may be made of water ice and are somewhat rounded, which may indicate the action of fluids. [cite web |url=http://www.planetary.org/news/2005/0115_The_Planetary_Societys_Huygens_Weblog.html |title=New Images from the Huygens Probe: Shorelines and Channels, But an Apparently Dry Surface |author=Emily Lakdawalla |publisher=The Planetary Society |date=January 15 2005 |accessdate=2005-03-28]

On February 13, 2008, scientists announced that, according to Cassini data, Titan hosts within its polar lakes "hundreds of times more natural gas and other liquid hydrocarbons than all the known oil and natural gas reserves on Earth." The desert sand dunes along the equator, while devoid of open liquid, nonetheless hold more organics than all of Earth's coal reserves.cite web|url=http://www.space.com/scienceastronomy/080213-titan-oil.html |title=Titan Has More Oil Than Earth |date=February 13, [2008] |accessdate=2008-02-13] . In June 2008, "Cassini"'s Visible and Infrared Mapping Spectrometer confirmed the presence of liquid ethane beyond doubt in a lake in Titan's southern hemisphere. [cite web|title=Scientists Confirm Liquid Lake, Beach on Saturn's Moon Titan|author=Adam Hadhazy|url=http://www.sciam.com/article.cfm?id=liquid-lake-on-titan|work=Scientific American|year=2008|accessdate=2008-07-30]

Models of oscillations in Titan's atmospheric circulation suggest that over the course of a Saturnian year, liquid is transported from the equatorial region to the poles, where it falls as rain. This might account for the equatorial region's relative dryness.cite web|title=Tropical Titan|work=astrobio.net|year=2007|url=http://www.astrobio.net/news/article2485.html|accessdate=2007-10-16]

Named lakes and seas

Titanian "maria" (large hydrocarbon seas) are named after sea monsters in world mythology.

Features labeled "lacus" are believed to be methane lakes. They are named after lakes on Earth.

References