Cassini mission completes 100th fly of Titan
BY STEPHEN CLARK
Posted: March 7, 2014
NASA's Cassini spacecraft, in the final months of its first decade spiraling around Saturn, zipped past the moon Titan on Thursday for the 100th time, continuing an unbroken string of flybys of one of the most Earth-like worlds in the known universe.
Titan is enveloped in an orange haze and thick nitrogen-rich atmosphere producing methane rainfall. With temperatures dipping as low as minus 290 degrees Fahrenheit (minus 179 degrees Celsius), the moon harbors rivers and lakes of liquid ethane and methane. Blocks of rock-hard ice dot the landscape.
Saturn's largest moon resembles how Earth might have looked as life first sprang up.
"Titan is a laboratory for how simple life got started on Earth," said Linda Spilker, Cassini's project scientist at the Jet Propulsion Laboratory in Pasadena, Calif.
Cassini's sojourn around Saturn began in 2004 after a seven-year cruise from Earth. The nuclear-powered probe's mission was extended twice until September 2017 as Saturn's northern hemisphere transitions from spring to summer.
More intense storms or hurricane-like cyclones could pop up in Titan's northern hemisphere as it receives more sunlight with the onset of summer, she said.
The approaching summer also allows Titan's northern lakes and seas to shine brighter in near-infrared, giving scientists better data on their composition. Scientists also hope to resolve waves on Titan's hydrocarbon lakes.
Such surface features are invisible to the eye, but specialized instruments aboard Cassini can peer through Titan's clouds in other wavelengths.
Cassini is currently in the solstice mission, and the mission's extension to 2017 will allow the probe to follow a complete seasonal cycle at Saturn -- from northern winter to northern summer.
During Thursday's flyby, scientists planned to analyze radio signals beamed down from Cassini to assess the presence of a global ocean of liquid water hidden underneath Titan's icy crust.
Researchers announced in 2012 they discovered Titan likely concealed volumes of liquid water between the moon's outer shell and rocky interior. They made the conclusion after proving the strong tug of Saturn's gravity created bigger tidal bulges than predicted if the moon was made entirely of solid rock.
Cassini's radio science experiment works by detecting subtle changes in communications signals from the spacecraft picked up by ground stations. Scientists can learn about the materials the signal passes through by observing the behavior of the radio waves once they arrive on Earth.
The radio investigation will help measure short-period changes in Titan's gravity field caused by Saturn's tidal forces, determine the shape of the moon and fluctuations in Titan's gravity, and examine the mechanics of ice flows on the moon's surface, according to NASA.
Thursday's encounter was the third of 11 close approaches between Cassini and Titan this year. Officials will devote other encounters to observe Titan's interaction with the solar wind, map its lakes and terrain, and profile the moon's atmosphere, which is rich in organic molecules.
Scientists employ Cassini's sensor suite to look at many of Saturn's other moons, such as Enceladus, which is covered in an icy shell with plumes of vapors shooting into space from fissures near the moon's south pole.
Running low on fuel, the $3.2 billion Cassini mission is due to end in September 2017 with a guided crash into Saturn to cleanly dispose of the spacecraft and its toxic components, ensuring Saturn's moons and their potential biospheres are preserved for future research.
Follow Stephen Clark on Twitter: @StephenClark1.
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