Cassini’s Last Photo of Titan Unveils the Methane Seas and Lakes on Saturn’s Largest Moon

3년 전

 Four days before Cassini’s epic dive into the atmosphere of Saturn, which brought its pioneering 13-year mission to an end, the spacecraft took one final look at Titan, the gas giant’s largest moon. The encounter was forever immortalized in an intriguing photo, which enhances the enigma around this bizarre Saturnian moon.“Titan is a fascinating place that really teases us with some of its mysteries,” said Elizabeth Turtle, a scientist at Johns Hopkins Applied Physics Lab.As the Inquisitr previously reported, the 1,600-mile-wide moon — which is half as big as Earth’s moon and ranks among the largest natural satellites of the solar system — is shrouded in a hazy atmosphere that conceals its surface features, hiding them from our sight.But in this last snapshot of Titan, Cassini has managed to peer through the moon’s atmosphere and capture a unique view of its north pole.According to NASA’s Jet Propulsion Laboratory (JPL), which designed and built Cassini, the image reveals an important clue about the moon’s atmosphere, pointing to an unexpected difference between the southern and the northern summer on Titan.Taken on September 11, 2017, by Cassini’s Imaging Science Subsystem (ISS) — specifically its narrow-angle camera, sensitive to near-infrared wavelengths — the photo showcases Titan’s northern seas and lakes.Unlike the ones found on Earth, the seas and lakes on Titan are filled with liquid hydrocarbons, mainly methane and ethane, the Inquisitr reported last year, shortly after the Cassini mission ended in a literal blaze of glory on September 15, 2017.“Cassini’s final image of the mysterious moon’s northern lakes and seas leaves us with more questions than answers,” JPL wrote on Twitter on September 13. 

 The left side of the photo is dominated by Kraken Mare, the largest known body of liquid on Titan. Named after the legendary sea monster, Kraken Mare stretches for 730 miles (1,200 kilometers) and is believed to be larger than the Caspian Sea on Earth.The center of the photo is occupied by Titan’s other two large methane seas, the 240-mile-wide (390 kilometers) Punga Mare and the slightly bigger Ligeia Mare, which measures 300-mile (500 kilometers) across.These are not the same maria seen on Earth’s moon, which earned their moniker after initially being mistaken for actual seas. Closer to home, lunar maria actually represent dark volcanic plains, the Inquisitr recently reported.The left side of the Cassini photo is populated by numerous methane lakes, which are fed liquid hydrocarbons by rainfall and underground streams, notes JPL.But while methane seas and lakes certainly make for a captivating sight, the striking thing about this Cassini image is a small detail that speaks volumes about the Titan’s weather.Captured from a distance of nearly 87,000 miles (140,000 kilometers) from Titan, the photo shows a few small clouds between Punga Mare and Ligeia Mare. This is in stark contrast with the richer cloud activity spotted by Cassini during the southern summer and imaged in July, 2004, above the moon’s south pole (images available on the JPL website here and here).“We expected more symmetry between the southern and northern summer,” said Turtle. “In fact, atmospheric models predicted summer clouds over the northern latitudes several years ago. So, the fact that they still hadn’t appeared before the end of the mission is telling us something interesting about Titan’s methane cycle and weather.” 

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