Cassini Limns Dione One Last Time

A few days ago, NASA’s Cassini spacecraft flew past Saturn’s moon Dione, and scientists at mission control were urgently awaiting new images of Cassini’s flyby until today. Cassini slipped by Dione at less than 295 miles from the surface at 2:33 p.m. Monday afternoon. The space craft has been orbiting the gas giant Saturn since 2004, and this is the latest of a series of “gravity science investigations” of an amalgam of Saturn’s 62 identified moons. Back in 2011, Cassini made an even closer flyby of the moon, skimming by at just 60 miles’ altitude.

Cassini’s cameras and spectrometers were active during the flyby, and they worked together to send NASA high-resolution imagery of Dione’s north pole. The images ought to help scientists come to a better understanding of Dione’s internal structure.

The images released are of such high resolution that an observer can see distances of a few feet. In addition to its other instruments, Cassini also made use of a Composite Infrared Spectrometer to map regions of the icy moon that seem to trap heat fairly well.


In doing this, Cassini has completed its fifth encounter with Dione. Such perilously close flybys require the most precise maneuvering to navigate the spacecraft along its optimum course. The spacecraft engaged a twelve-second burn of its thrusters on the 9th of August to perfect its trajectory.

Cassini’s original flyby of Dione occurred on October 11th, 2005, and since then, each flyby has revealed the moon’s crisp luminescence only glimpsed during the Voyager mission.


What we see in these new images are braided canyons with shining walls. Scientists hope to learn if this new data will reveal evidence of geologic activity on Dione that at all resembles Enceladus, Saturn’s other, geyser-shooting moon.

“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,” laments Bonnie Buratti, a Cassini science team member at NASA’s Jet Propulsion Laboratory in Pasadena, California.


Cassini, along with its Huygens lander, originally launched on the top of a U.S. Air Force Titan IVB rocket from Cape Canaveral Air Force Station on October 15, 1997. Seven years later, after making several flybys of Earth, Venus and Jupiter, the probe made orbit with Saturn on July 1, 2004. The lander, Huygens, then separated from Cassini on December 25th of that year, and made a successful landing on Titan, on January 14th, 2005.


After a few more flybys of Titan and Enceladus later this year, Cassini will leave Saturn’s equatorial plane to prepare for its mission’s final phase. In 2017 Cassini will investigate Saturn’s rings by repeatedly diving in and out, in a sinusoidal fashion.

“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.”