Spaceflight Insider

Cassini makes final flyby of Saturn’s moon Dione

A view of Saturn's moon Dione captured by NASA's Cassini spacecraft during a close flyby on June 16, 2015. The diagonal line near upper left is the rings of Saturn, in the distance. Photo Credit: NASA/JPL-Caltech/Space Science Institute

A view of Saturn’s moon Dione captured by NASA’s Cassini spacecraft during a close flyby on June 16, 2015. The diagonal line near upper left is the rings of Saturn, in the distance. (Click to enlarge) Photo Credit: NASA/JPL-Caltech/Space Science Institute

NASA’s Cassini spacecraft made its final close flyby of Saturn’s moon Dione on August 17, 2015. The spacecraft’s closest approach, which brought it within 295 miles (474 kilometers) of Dione’s surface, occurred at 2:33 p.m. EDT (18:33 GMT). The Cassini team expects fresh images from the encounter to arrive on Earth in a few days.

Cassini was expected to get a high-resolution view of Dione’s north pole at a resolution of only a few feet using its cameras and spectrometers. Cassini also used its Composite Infrared Spectrometer to map regions of the icy moon that are especially good at trapping heat. Gravity-science data from the flyby will improve researchers’ knowledge of Dione’s internal structure and allow comparisons to other moons of Saturn.

The Cassini spacecraft in orbit above the gas giant Saturn NASA JPL image posted on SpaceFlight Insider

Cassini has been orbiting Saturn since July 1, 2004. Image Credit: NASA / JPL

The flyby was Cassini’s fifth encounter with Dione during the spacecraft’s time at Saturn. Close flybys require precision maneuvering to steer the spacecraft toward the desired course above the moon. Cassini executed a 12-second burn of its thrusters on August 9 to fine-tune its trajectory for the most recent encounter.

Cassini’s first targeted flyby of Dione was on October 11, 2005. Its closest-ever flyby brought in to within 60 miles (100 kilometers) of Dione’s surface in December 2011. Cassini’s close flybys have revealed high-resolution views of the bright wispy terrain first seen during the Voyager mission. Images taken by Cassini have revealed these bright features to be a system of braided canyons with bright walls. Scientists are eager to find out if the data from the most recent flyby show evidence of geological activity on Dione similar to Saturn’s geyser-spouting moon Enceladus.

“Dione has been an enigma, giving hints of active geologic processes, including a transient atmosphere and evidence of ice volcanoes. But we’ve never found the smoking gun. The fifth flyby of Dione will be our last chance,” said Bonnie Buratti, a Cassini science team member at NASA’s Jet Propulsion Laboratory in Pasadena, California.

The Cassini orbiter, along with the Huygens lander, launched atop a U.S. Air Force Titan IVB rocket from Cape Canaveral Air Force Station on October 15, 1997. The spacecraft made a seven-year voyage to Saturn which included flybys of Earth, Venus, and Jupiter. Cassini went into orbit around Saturn on July 1, 2004. The Huygens lander separated from Cassini on December 25, 2004, and landed successfully on Saturn’s moon Titan on January 14, 2005.

Following a series of close flybys of Saturn’s moons Titan and Enceladus in late 2015, Cassini will depart Saturn’s equatorial plane to begin the year-long setup of the mission’s final phase. During 2017, Cassini will repeatedly dive through the space between Saturn’s rings.

“This will be our last chance to see Dione up close for many years to come,” said Scott Edgington, Cassini mission deputy project scientist at JPL. “Cassini has provided insights into this icy moon’s mysteries, along with a rich data set and a host of new questions for scientists to ponder.”


Jim Sharkey is a lab assistant, writer and general science enthusiast who grew up in Enid, Oklahoma, the hometown of Skylab and Shuttle astronaut Owen K. Garriott. As a young Star Trek fan he participated in the letter-writing campaign which resulted in the space shuttle prototype being named Enterprise. While his academic studies have ranged from psychology and archaeology to biology, he has never lost his passion for space exploration. Jim began blogging about science, science fiction and futurism in 2004. Jim resides in the San Francisco Bay area and has attended NASA Socials for the Mars Science Laboratory Curiosity rover landing and the NASA LADEE lunar orbiter launch.

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