Titan, a moon with lakes and beaches!
Scientists suggest a new destination for beach holidays in the Solar System. Too bad it's not easy to get there. Researchers published in the journal Nature, the identification of a dark lake, surrounded by a lighter coastal region and a "beach" on the surface of Titan, Saturn's largest moon. The lake - shaped like a shoe sole - is the first extraterrestrial liquid body and probably contains hydrocarbons, simple compounds also common on Earth.
"This is the first conclusive evidence of the presence of liquid hydrocarbons on Titan," according to the lead author of the article, Robert Brown, professor of planetary science at the Lunar and Planetary Laboratory (LPL) at the University of Arizona in Tucson.
Instruments aboard NASA's Cassini orbiter around Saturn and its satellites, including Titan, since June 2004, reveal the presence of liquid ethane - an organic compound containing carbon - in an area roughly the same dimensions as Lake Ontario ( one of the Great Lakes between Canada and the United States) in the Southern Hemisphere of Titan. Similar dark regions have also been detected in the Northern Hemisphere, indicating that probably Titan's surface is dotted with hydrocarbon “seas”. Researchers confirmed the presence of liquid ethane from results obtained by the Visible and Infrared Mapping Spectrometer ( VIMS) on board Cassini, who detected hydrocarbon lines in these bands of the spectrum. Ethane is formed from the action of sunlight on the methane in Titan's atmosphere. The ethane in the atmosphere is believed to condense into clouds that precipitate in the form of rain. As it drains over Titan's surface, the rain makes its way forming currents that end up being dammed in real lakes of ethane.
Titan has attracted the attention of astronomers thanks to its atmosphere formed by an orange mist, which extends 965 kilometers from its surface. Nitrogen is the dominant element, although there are traces of methane and other hydrocarbons, including propane. With a diameter of 5,150 km, Titan is larger than Mercury and only 25% smaller than Mars, making it the second largest moon in the Solar System, just after Ganymede, Jupiter's moon.
Liquid ethane or methane was already suspected on Titan's surface. This discovery confirmed the idea that Titan has a "hydrological cycle" similar to that of Earth. But the liquid that forms clouds, rain and then evaporates again is not water, but methane and ethane, recalls the work's co-author, Christophe Sotin, planetary scientist at NASA's Jet Propulsion Laboratory (JPL) in Pasadena , Calif., In addition to putting an end to debates about the existence of liquids on Titan, this discovery could alter the course of future missions. Both NASA and the European Space Agency (Esa) are considering returning to Titan; these new observations support the idea of sending a vehicle that lands on a lake - a floating probe - to take samples of its composition, says Ralph Lorenz, planetary scientist at the Laboratory of Applied Physics at Johns Hopkins University in Laurel, Maryland.
The liquid pool, called Ontario Lacus, absorbs practically all the incident light which gives it a dark hue, according to Brown from LPL. The data also reveal that the lake's surface is calm, without ripples or waves, which for Brown is surprising. He and his team hoped to find waves caused by possible surface winds.
There is little chance of life on Titan. “It's just a matter of fertile imagination,” says Jonathan Lunine, a professor of planetary science and physics at JPL, who did not participate in the study. "If a terrestrial organism is left on the surface of Titan, it will surely die." But, the probability of exotic forms of life in a liquid hydrocarbon environment is not ruled out.
Confirmation of the presence of organic compounds and nitrogen means that Titan has a chemical composition very similar to that of the primitive Earth, when life began to develop. "These compounds form the basis for the future formation of more complex molecules," says Brown.
The dominant idea is that the chemistry needed to create molecules with the capacity to replicate and store information - like DNA - did not develop on Titan, due to the extremely low temperatures (average of -181º C). The lack of liquid water on the surface - the main ingredient for the formation of life as we know it - is another reason that may have prevented the evolution of life on Titan, if it ever emerged.
But Brown warns that volcanoes and other tectonic activities can add energy and even water to this mix. "Although nobody believes that much," says Brown, if life finds a way to develop on Titan, it will definitely be in a very different climate than ours.
