Cassini Spots Mini Nile River On Saturn Moon

Scientists with NASA's Cassini mission have spotted what appears to be a miniature, extraterrestrial likeness of Earth's Nile River: a river valley on Saturn's moon Titan that stretches more than 200 miles (400 kilometers) from its "headwaters" to a large sea. It is the first time images have revealed a river system this vast and in such high resolution anywhere other than Earth.

"

This image from NASA's Cassini spacecraft shows a vast river system on Saturn's moon Titan. It is the first time images from space have revealed a river system so vast and in such high resolution anywhere other than Earth [Credit: NASA/JPL-Caltech/ASI]"

Scientists deduce that the river, which is in Titan's north polar region, is filled with liquid hydrocarbons because it appears dark along its entire length in the high-resolution radar image, indicating a smooth surface.

"Though there are some short, local meanders, the relative straightness of the river valley suggests it follows the trace of at least one fault, similar to other large rivers running into the southern margin of this same Titan sea," said Jani Radebaugh, a Cassini radar team associate at Brigham Young University, Provo, Utah. "Such faults -- fractures in Titan's bedrock -- may not imply plate tectonics, like on Earth, but still lead to the opening of basins and perhaps to the formation of the giant seas themselves."

The new image is available online at: http://www.nasa.gov/mission pages/cassini/multimedia/pia16197.html.

Titan is the only other world we know of that has stable liquid on its surface. While Earth's hydrologic cycle relies on water, Titan's equivalent cycle involves hydrocarbons such as ethane and methane. In Titan's equatorial regions, images from Cassini's visible-light cameras in late 2010 revealed regions that darkened due to recent rainfall. Cassini's visual and infrared mapping spectrometer confirmed liquid ethane at a lake in Titan's southern hemisphere known as Ontario Lacus in 2008.

"Titan is the only place we've found besides Earth that has a liquid in continuous movement on its surface," said Steve Wall, the radar deputy team lead, based at NASA's Jet Propulsion Laboratory, Pasadena, Calif. "This picture gives us a snapshot of a world in motion. Rain falls, and rivers move that rain to lakes and seas, where evaporation starts the cycle all over again. On Earth, the liquid is water; on Titan, it's methane; but on both it affects most everything that happens."

The radar image here was taken on Sept. 26, 2012. It shows Titan's north polar region, where the river valley flows into Kraken Mare, a sea that is, in terms of size, between the Caspian Sea and the Mediterranean Sea on Earth. The real Nile River stretches about 4,100 miles (6,700 kilometers). The processes that led to the formation of Earth's Nile are complex, but involve faulting in some regions.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and ASI, the Italian Space Agency. NASA's Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA's Science Mission Directorate, Washington. The Cassini orbiter was designed, developed and assembled at JPL. The radar instrument was built by JPL and the Italian Space Agency, working with team members from the US and several European countries. JPL is a division of the California Institute of Technology in Pasadena.

"Source: NASA/Jet Propulsion Laboratory [December 12, 2012]"

Cassini Sees Precursors To Aerosol Haze On Titan

Scientists working with data from NASA's Cassini mission have confirmed the presence of a population of complex hydrocarbons in the upper atmosphere of Saturn's largest moon, Titan, that later evolve into the components that give the moon a distinctive orange-brown haze. The presence of these complex, ringed hydrocarbons, known as polycyclic aromatic hydrocarbons (PAHs), explains the origin of the aerosol particles found in the lowest haze layer that blankets Titan's surface. Scientists think these PAH compounds aggregate into larger particles as they drift downward.

"

NASA's Cassini spacecraft looks toward the night side of Saturn's largest moon and sees sunlight scattering through the periphery of Titan's atmosphere and forming a ring of color [Credit: NASA/JPL-Caltech/Space Science Institute]"

"With the huge amount of methane in its atmosphere, Titan smog is like L.A. smog on steroids," said Scott Edgington, Cassini deputy project scientist based at NASA's Jet Propulsion Laboratory, Pasadena, Calif. "These new papers using Cassini data shed light on how the heavy, complex hydrocarbon molecules that make up Titan's smog came to form out of the simpler molecules in the atmosphere. Now that they have been identified, the longevity of Cassini's mission will make it possible to study their variation with Titan seasons."

Of all the bodies in the solar system, Saturn's largest moon, Titan, has the atmosphere most resembling that of Earth. Like that of our planet, Titan's atmosphere is largely composed of molecular nitrogen. Unlike Earth's atmosphere, however, Titan's contains only small traces of oxygen and water. Another molecule, methane, plays a similar role to that of water in Earth's atmosphere, and makes up about 2 percent of Titan's atmosphere. Scientists have speculated that the atmosphere of this moon may resemble that of our planet in its early days, before primitive living organisms enriched it with oxygen via photosynthesis.

When sunlight or highly energetic particles from Saturn's magnetic bubble hit the layers of Titan's atmosphere above about 600 miles (1,000 kilometers), the nitrogen and methane molecules there are broken up. This results in the formation of massive positive ions and electrons, which trigger a chain of chemical reactions, producing a variety of hydrocarbons -- a wide range of which have been detected in Titan's atmosphere. These reactions eventually lead to the production of carbon-based aerosols, large aggregates of atoms and molecules that are found in the lower layers of the haze that enshrouds Titan, well below 300 miles (500 kilometers). The process is similar to Earth, where smog starts with sunlight breaking up hydrocarbons that are emitted into the air. The resulting pieces recombine to form more complex molecules.

Aerosols in Titan's lower haze have been studied using data from the descent of the European Space Agency's Huygens probe, which reached the surface in 2005, but their origin remained unclear. New studies analyzing data from Cassini's visual and infrared mapping spectrometer (VIMS) gathered in July and August 2007 might solve the problem. One new study of Titan's upper atmosphere in the Astrophysical Journal describes the detection of the PAHs, which are large carbon-based molecules that form from the aggregation of smaller hydrocarbons.

"

This illustration shows the various steps that lead to the formation of the aerosols that make up the haze on Titan, Saturn's largest moon [Credit: ESA/ATG medialab]"

"We can finally confirm that PAHs play a major role in the production of Titan's lower haze, and that the chemical reactions leading to the formation of the haze start high up in the atmosphere," said this paper's lead author Manuel L'opez-Puertas from the Astrophysics Institute of Andalucia in Granada, Spain. "This finding is surprising: we had long suspected that PAHs and aerosols were linked in Titan's atmosphere, but didn't expect we could prove this with current instruments."

The team of scientists had been studying the emission from various molecules in Titan's atmosphere when they stumbled upon a peculiar feature in the data. One of the characteristic lines in the spectrum -- from methane emissions -- had a slightly anomalous shape, and the scientists suspected it was hiding something.

Bianca Maria Dinelli from the Institute of Atmospheric Sciences and Climate (part of the National Research Council) in Bologna, Italy, was the lead author of a related paper in the journal Geophysical Research Letters. She and her colleagues conducted a painstaking investigation to identify the chemical species responsible for the anomaly. The additional signal was found only during daytime, so it clearly had something to do with solar irradiation.

"The central wavelength of this signal, about 3.28 microns, is typical for aromatic compounds -- hydrocarbon molecules in which the carbon atoms are bound in ring-like structures," said Dinelli.

The scientists tested whether the unidentified emission could be produced by benzene, the simplest aromatic compound consisting of one ring only, which had been detected earlier in Titan's atmosphere. However, the relatively low abundances of benzene are not sufficient to explain the emission that had been observed.

After they ruled out benzene, the scientists tried to reproduce the observed emission with the more complex PAHs. They checked their data against the NASA Ames PAH Infrared Spectral Data Base. And they were successful: the data can be explained as emission by a mixture of many different PAHs, which contain an average of 34 carbon atoms and about 10 rings each.

"PAHs are very efficient in absorbing ultraviolet radiation from the sun, redistributing the energy within the molecule and finally emitting it at infrared wavelengths," said co-author Alberto Adriani from the Institute for Space Astrophysics and Planetology at Italy's National Institute for Astrophysics (INAF) in Rome. He is part of the Cassini-VIMS co-investigators team and started this investigation. He manages the team that collected and processed VIMS data.

These hydrocarbons also are peculiarly capable of sending out profuse amounts of infrared radiation even in the rarefied environment of Titan's upper atmosphere, where the collisions between molecules are not very frequent. The molecules are themselves an intermediate product, generated when radiation from the sun ionizes smaller molecules in the upper atmosphere of Titan that then coagulate and sink.

The Cassini-Huygens mission is a cooperative project of NASA, ESA and Italy's ASI space agency. The Jet Propulsion Laboratory manages the Cassini-Huygens mission for NASA's Science Mission Directorate, Washington DC, USA. The visual and infrared mapping spectrometer team is based at the University of Arizona, Tucson. The California Institute of Technology in Pasadena manages JPL for NASA.

"Source: NASA/Jet Propulsion Laboratory [June 05, 2013]"