Saturday afternoon, NASA’s Cassini spacecraft will bid farewell to one of the solar system’s most intriguing bodies. At a distance of 3,106 miles, the spacecraft will soar past Enceladus for one last look.

This weekend’s flyby will not be even close to the closest flyby. And it was designed that way. Cassini’s mission team wants the spacecraft’s Composite Infrared Spectrometer (CIRS) instrument to measure heat flows across a good chunk of Enceladus’ south polar region.

“The distance of this flyby is in the sweet spot for us to map the heat coming from within Enceladus — not too close, and not too far away. It allows us to map a good portion of the intriguing south polar region at good resolution,” said Mike Flasar, CIRS team lead at NASA’s Goddard Space Flight Center.

The timing of the last visit is perfect. When Cassini reached Saturn more than ten years ago, Enceladus’ south pole was enjoying summer. Today, darkness has a firm grip on the region. Why does timing matter? With no heating from the sun, scientists can get more accurate measurements on heat flows coming from the watery moon’s interior.

How Enceladus changed the Cassini mission

Cassini’s mission to the Saturn system has been a resounding success. Many of the historic discoveries center around the small, icy Enceladus. When scientists discovered geologic activity on Enceladus shortly after Cassini’s arrival, they knew the moon was special. The mission flight plan was adjusted to get as many quality visits to the moon as possible.

Enceladus plumes

Most of the excitement centers around its plumes and what lies beneath. The icy plumes were first detected in 2005. Additional discoveries showed icy material coming from fractures near the south pole. Last year, NASA scientists announced evidence of a regional subsurface sea. And that was revised after new data revealed a stunning global ocean this year.

Saturn’s Smallest Moons Clean Up

“Cassini’s legacy of discoveries in the Saturn system is profound,” said Spilker. “We won’t get this close to Enceladus again with Cassini, but our travels have opened a path to the exploration of this and other ocean worlds,” said Linda Spilker, Cassini project scientist at NASA’s JPL.

Enceladus discoveries continue

The latest data from Cassini is revealing the pH of the moon’s ocean. It’s about the same as Windex or soapy water. What does this mean? Geochemist Christopher Glein explains to Discovery News.

“We think that what happened on Enceladus, and which could still be happening today, is that there were geochemical reactions between magnesium and iron-rich rocks in Enceladus’ core reacting with ocean water. Those reactions led to the high pH.”

The next step? Finding hydrogen. That would be a game changer. “Hydrogen … has the potential to drive the synthesis of organic molecules — and much more,” Glein said.

New data from Cassini’s October flyby is being presented this week at the American Geophysical Union. Keep an eye on their YouTube channel to see if they upload any of the presentations.

2016 Will be the Year of Titan

Saturday’s flyby will be the last of 2015. Close flybys get started again on January 15 when Cassini is 2,372 miles away from Titan. It will be the first of ten flybys of Titan in 2016.

The closest Titan flybys will be a pair next summer. On June 7 and July 25, Cassini will soar past Saturn’s largest moon at a distance of 606 miles.

You can check out where Cassini is scheduled to be in 2016 here.

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