NASA's Cassini probe burned up in Saturn's atmosphere about a year ago, but a newly-released image shows that its last days were anything but idle. Four days before its fiery end, Cassini's ISS narrow-angle camera captured a mosaic view of the Saturnian largest satellite Titan's north polar lakes filled with liquid methane and ethane, raising new question about the enigmatic moon.

On September 15, 2017, the unmanned Cassini probe's 20-year mission to Saturn came to a spectacular finish as it made a controlled entry into the planet's atmosphere. At 7:55 am EDT, the spacecraft hit the atmosphere at 70,000 mph (113,000 km/h), tumbled out of control and burned up like a meteor.

The reason for this dramatic finish is that Cassini had exhausted the propellant for its thrusters and if it had simply been left in orbit, there was a remote chance that one day in the future it might crash on one of Saturn's moons, contaminating it with terrestrial microbes. However, the end of the Cassini mission left a lot of questions to be answered.

The new image taken from an altitude of 87,000 miles (140,000 km) shows Punga Mare, which is a 240-mile (390-km)-wide lake that can be seen at the center, with Ligeia Mare (300 mi/500 km wide) just below and the 730-mile (1,200-km)-wide Kraken Mare to the left. Along with these is a scattering of smaller lakes. The question is, how did these lakes form?

According to NASA, another poser is the weather on Titan. With its methane atmosphere that has a surface pressure 1.45 times that of Earth, Titan has is own methane cycle that's analogous to Earth's water cycle marked by evaporation, cloud formation, rainfall, surface and runoff into rivers before collecting in lakes and seas. The problem is that while clouds form readily over the Titanian south pole in the local summer, that isn't the case at the north pole.

"We expected more symmetry between the southern and northern summer," says Elizabeth Turtle of the Johns Hopkins Applied Physics Lab and the Cassini Imaging Science Subsystem (ISS) team. "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. Titan is a fascinating place that really teases us with some of its mysteries."

Source: NASA

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