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[cameron]

As part of Cassini's second extended mission ("Cassini Solstice Mission") on its tour of the Saturn system, two of the final three targeted flybys of Enceladus were completed this month. Most notably was the deepest-ever dive through the icy plume of Enceladus on Oct. 28, 2015.

COMPLETED: 14 Oct 2015: Cassini will get the best views yet of the moon's north polar regions during this flyby at an altitude of 1,142 miles, or 1,839 kilometers.

COMPLETED: 28 Oct 2015: Cassini will make a daring flight through the moon's famous plume only 30 miles (48 kilometers) above Enceladus' south pole. The flyby is Cassini's deepest-ever dive through the jets. The encounter will allow Cassini to obtain the most accurate measurements yet of the plume's composition, and new insights into the ocean world beneath the ice.

19 Dec 2015: Cassini's final targeted flyby will allow the spacecraft to measure heat flow from the moon's interior at an altitude of 3,106 miles, or 4,999 kilometers.

http://solarsystem.nasa.gov/finalflybys


Press release for the first flyby: "Closest Northern Views of Saturn's Moon Enceladus"

Craters Crowd the North

This view from NASA's Cassini spacecraft shows battered terrain around the north pole of Saturn's icy moon Enceladus. Craters crowd and overlap each other, each one recording an impact in the moon's distant past.
The moon's north pole lies approximately at the top of this view from Cassini's wide-angle camera. A companion view from the narrow-angle camera (PIA19660) shows the pole at a resolution about ten times higher.
North on Enceladus is up. The image was taken in visible light by Cassini on Oct. 14, 2015.
The view was acquired at a distance of approximately 4,000 miles (6,000 kilometers) from Enceladus and at a Sun-Enceladus-spacecraft, or phase, angle of 8 degrees. Image scale is 1,093 feet (333 meters) per pixel.

A Fractured Pole

Scientists expected the north polar region of Enceladus to be heavily cratered, based on low-resolution images from the Voyager mission, but high-resolution Cassini images show a landscape of stark contrasts. Thin cracks cross over the pole -- the northernmost extent of a global system of such fractures. Before this Cassini flyby, scientists did not know if the fractures extended so far north on Enceladus.
North on Enceladus is up. The image was taken in visible green light with the Cassini spacecraft narrow-angle camera.
The view was acquired at a distance of approximately 4,000 miles (6,000 kilometers) from Enceladus and at a Sun-Enceladus-spacecraft, or phase, angle of 9 degrees. Image scale is 115 feet (35 meters) per pixel.

Saturnian Snowman

NASA's Cassini spacecraft spied this tight trio of craters as it approached Saturn's icy moon Enceladus for a close flyby on Oct. 14, 2015. The craters, located at high northern latitudes, are sliced through by thin fractures -- part of a network of similar cracks that wrap around the snow-white moon.
The image was taken in visible light with the Cassini spacecraft narrow-angle camera on Oct. 14, 2015 at a distance of approximately 6,000 miles (10,000 kilometers) from Enceladus. Image scale is 197 feet (60 meters) per pixel.
The image was taken with the Cassini spacecraft narrow-angle camera on Oct. 14, 2015 using a spectral filter which preferentially admits wavelengths of ultraviolet light centered at 338 nanometers.

Press release for the plume drive: "Saturn's Geyser Moon Shines in Close Flyby Views"

Mission Overview: "Enceladus Flyby 'E-21': Deepest Dive Through the Plume"

Key scientific expectations for this flyby
Scientists are looking forward to several important scientific results from the Oct. 28 flyby. These results will not be available immediately -- they will take several months of careful analysis, and would be published in a peer-reviewed journal.

1. Confirm presence of molecular hydrogen (H2)
• This measurement will be accomplished using Cassini's sensor that sniffs the gases in the plume (called INMS)
• Confirmation of H2 would be an independent line of evidence that hydrothermal activity is taking place in the Enceladus ocean, on the seafloor
• Amount of H2 Cassini measures would reveal how much hydrothermal activity is going on in the ocean.
• This has implications for the amount of energy available for creating a habitable environment in the ocean

2. Better understand the chemistry of material in the plume
• Cassini's dust detector (called CDA) will obtain spectra of the heavier particles only found at low altitudes nearer to the plume's source
• Among these heavier particles, Cassini may detect new, more complex organic molecules (albeit with not enough resolution to confirm if they are biological in nature)
• Scientists think these heavier particles carry material from the sub-surface ocean
• Scientists are doing laboratory experiments to create a catalog they can refer to of chemical fingerprints (or spectra) for fragments of complex organic molecules Cassini might detect

3. Determine the nature of the plume sources
• Is the plume made up of tight, column-like jets or curtain-like eruptions that run along the length of the tiger stripe fractures (or both)?
• How much icy material are the plumes actually spraying out? Scientists are still not sure, and the amount has major implications for how long the moon might have been active.
• This measurement will be accomplished by part of Cassini's CDA instrument called the high-rate detector, which can count the impacting ice particles from the plume (over 10,000 per second) in real-time.

Important points about the encounter
• This flyby will not detect life. Cassini does not have the capability to do that. Scientists hope the flyby will provide powerful new insights about how habitable the ocean environment is within Enceladus.
• The flyby will sample material coming from an ocean within an icy moon -- a true "ocean world" orbiting Saturn.
• Going closer to the south pole allows Cassini to go deeper into the plume of icy spray. Scientists expect Cassini will have greater sensitivity to the chemistry of the plume, including organic molecules, than during previous flybys.
• This is the deepest-ever dive through the Enceladus plume, which Cassini discovered 10 years ago, not long after arriving at Saturn.
• Cassini was not specifically designed for this kind of maneuver -- sampling active cryovolcanic plumes -- but it has a powerful suite of science instruments that made this sort of science possible.

NASA's Cassini spacecraft captured this view as it neared icy Enceladus for its closest-ever dive past the moon's active south polar region.

The south polar region of Saturn's active, icy moon Enceladus awaits NASA's Cassini spacecraft in this view, acquired on approach to the mission's deepest-ever dive through the moon's plume of icy spray.

This unprocessed view of Saturn's moon Enceladus was acquired by NASA's Cassini spacecraft during a close flyby of the icy moon on Oct. 28, 2015.

During its closest ever dive past the active south polar region of Saturn's moon Enceladus

Following a successful close flyby of Enceladus, NASA's Cassini spacecraft captured this artful composition of the icy moon with Saturn's rings beyond.

^Raw image. No caption. More processed images and science data will be released later. Raw images can be viewed here: http://saturn.jpl.nasa.gov/photos/raw/index.cfm?start=1&storedQ=2760015

A couple of other things I thought was neat. Stabilized image set from the first flyby:

https://twitter.com/elakdawalla/status/655103689330327552

Image set from earlier this year, "Changing View of the Enceladus Plume"

This animated sequence of images, captured by NASA's Cassini spacecraft, shows changes in the brightness of the Enceladus plume during a 6.5-hour observation.

The change in plume brightness during this observation is due almost entirely to the changing sun-Enceladus-spacecraft angle, or phase angle. Over the course of the observation, the phase angle changed from 149 to 155 degrees.

Tiny water ice particles make up the bulk of the plume as imaged by Cassini's cameras. These particles tend to scatter light toward the viewer much more at higher phase angles than lower ones. Imaging scientists process such images to remove variations in brightness due to the changing phase angle in order to study the plume's true variation in brightness. Observing how the brightness of the plume varies throughout the icy moon's orbit can help scientists understand the nature of the mechanisms that force material to Enceladus' surface.

http://saturn.jpl.nasa.gov/multimedia/videos/movies/PIA17198_PhotojournalVersion.mp4

 

[AstroNut325]

This flyby will not detect life. Cassini does not have the capability to do that. Scientists hope the flyby will provide powerful new insights about how habitable the ocean environment is within Enceladus

I sincerely hope it's very habitable!

 

[Archaeopteryx]

What a beautiful world.

 

[Elfforkusu]

I love how as they extend the mission further and further, the flybys get more and more reckless. :lol

As it should be!

 

[cameron]

I love how as they extend the mission further and further, the flybys get more and more reckless. :lol

As it should be!

The extended unplanned goals are always fun/interesting. The only bummer here is that after the recent Enceladus close flyby, Cassini won't get as close to the surface of any other system object until its entry into Saturn's atmosphere when fuel runs out.

A final nudge by a distant Titan on September 11, 2017 will deliver the death blow to Cassini, putting its periapsis below Saturn's clouds. Cassini will not survive that plunge, and the mision will come to an end on September 15.

 

[Habaneroguy]

I guess they consider everything at this point to be icing on the cake? That shot with Saturns rings is epic to say the least.

 

[Limited Edition]

I love how as they extend the mission further and further, the flybys get more and more reckless. :lol

As it should be!

Why not be reckless? It's long outlived it's original mission, so now everything is a crap shoot. It could last another ten years, or ten days. May as well get every bit of info possible before something goes wrong.

 

[Fenderputty]

What a beautiful world.

Agreed. Imagine standing on it's surface and looking at Saturn in the sky.

 

[Slayer-33]

That's some metroid prime level shit right there.

 

[Hidden One]

I shall name it Hoth.

 

[The Llama]

The outer planets in our solar system are pretty amazing. I can't wait until we send more spacecraft out to Uranus and Neptune. Feel like they're so underrated because they're so far away and hard to get to, but I bet they're amazingly beautiful and interesting.

 

[Dennis]

Tire tracks. Tire tracks everywhere.

 

[cameron]

Still waiting for the findings of the plume dive and the direct samples that were taken. The final targeted flyby happened on Saturday. No more Enceladus for Cassini. They released some media for it today.

NASA Press Release: "Cassini Completes Final Close Enceladus Flyby"

NASA's Cassini spacecraft has begun transmitting data and images from the mission's final close flyby of Saturn's active moon Enceladus. Cassini passed Enceladus at a distance of 3,106 miles (4,999 kilometers) on Saturday, Dec. 19, at 9:49 a.m. PST (12:49 p.m. EST).

"This final Enceladus flyby elicits feelings of both sadness and triumph," said Earl Maize, Cassini project manager at JPL. "While we're sad to have the close flybys behind us, we've placed the capstone on an incredible decade of investigating one of the most intriguing bodies in the solar system."

Cassini will continue to monitor activity on Enceladus from a distance, through the end of its mission in Sept. 2017. Future encounters will be much farther away -- at closest, more than four times farther than this latest encounter.

This was the 22nd Enceladus encounter of Cassini's mission. The spacecraft's discovery of geologic activity there, not long after arriving at Saturn, prompted changes to the mission's flight plan to maximize the number and quality of flybys of the icy moon.

"We bid a poignant goodbye to our close views of this amazing icy world," said Linda Spilker, the mission's project scientist at NASA's Jet Propulsion Laboratory in Pasadena, California. "Cassini has made so many breathtaking discoveries about Enceladus, yet so much more remains to be done to answer that pivotal question, 'Does this tiny ocean world harbor life?'"

The science goals:

The upcoming flyby will focus on measuring how much heat is coming through the ice from the moon's interior -- an important consideration for understanding what is driving the plume of gas and icy particles that sprays continuously from an ocean below the surface.

"Understanding how much warmth Enceladus has in its heart provides insight into its remarkable geologic activity, and that makes this last close flyby a fantastic scientific opportunity," said Linda Spilker, Cassini project scientist at NASA's Jet Propulsion Laboratory, Pasadena, California.

By design, the encounter will not be Cassini's closest. The flyby was designed to allow Cassini's Composite Infrared Spectrometer (CIRS) instrument to observe heat flow across Enceladus' south polar terrain.

"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, Greenbelt, Maryland.

"Enceladus, Old and New "

Enceladus dramatically displays the contrast between its older and newer terrain.

Newer surfaces (on the left in the image) will not have had time to accumulate craters. But as material sits exposed on the surface, impact scars build up, as in the more heavily cratered area on the top and right. Scientists can use this, along with estimates of how frequently impacts happen, to determine ages of surfaces of solid planets and of moons like Enceladus (313 miles or 504 kilometers across).

This view looks toward the anti-Saturn side of Enceladus. North on Enceladus is up and rotated 36 degrees to the right. The image was taken in green light with the Cassini spacecraft narrow-angle camera on Aug. 18, 2015.

The view was acquired at a distance of approximately 85,000 miles (137,000 kilometers) from Enceladus. Image scale is 2,680 feet (818 meters) per pixel.

"Features of the North"

NASA's Cassini spacecraft peered out over the northern territory on Saturn's moon Enceladus, capturing this view of two different terrain types. A region of older terrain covered in craters that have been modified by geological processes is seen at right, while at left is a province of relatively craterless, and presumably more youthful, wrinkled terrain. Cassini acquired the view during its final close flyby of Enceladus, on Dec. 19, 2015.

North on Enceladus is up and rotated 38 degrees to the left. The image was taken in polarized green light with the Cassini spacecraft narrow-angle camera.

The view was acquired at a distance of approximately 21,000 miles (34,000 kilometers) from Enceladus and at a Sun-Enceladus-spacecraft, or phase, angle of 145 degrees. Image scale is 668 feet (204 meters) per pixel.

"Ice and Atmosphere"

NASA's Cassini spacecraft paused during its final close flyby of Enceladus to focus on the icy moon's craggy, dimly lit limb, with the planet Saturn beyond.

Layers can be seen in the high hazes of Saturn's upper atmosphere, in the gradient that separates the planet from space.

North on Enceladus is up and rotated 27 degrees to the left. The image was taken with the Cassini spacecraft narrow-angle camera on Dec. 19, 2015, using a spectral filter, which preferentially admits wavelengths of near-infrared light.

The view was acquired at a distance of approximately 15,000 miles (24,000 kilometers) from Enceladus and at a Sun-Enceladus-spacecraft, or phase, angle of 147 degrees. Image scale is 479 feet (146 meters) per pixel.

"Frozen Fractures"

During its final close flyby of Saturn's moon Enceladus, NASA's Cassini spacecraft captured this view featuring the nearly parallel furrows and ridges of the feature named Samarkand Sulci.

This view is centered on terrain at 13 degrees north latitude, 336 degrees west longitude. The image was taken with the Cassini spacecraft narrow-angle camera on Dec. 19, 2015, using a spectral filter, which preferentially admits wavelengths of near-ultraviolet light.

The view was acquired at a distance of approximately 8,000 miles (12,000 kilometers) from Enceladus and at a Sun-Enceladus-spacecraft, or phase, angle of 58 degrees. Image scale is 243 feet (74 meters) per pixel.

Not related to the final targeted flyby, but still neat:
"Bull's-eye Moons "

Like a cosmic bull's-eye, Enceladus and Tethys line up almost perfectly for Cassini's cameras.

Since the two moons are not only aligned, but also at relatively similar distances from Cassini, the apparent sizes in this image are a good approximation of the relative sizes of Enceladus (313 miles or 504 kilometers across) and Tethys (660 miles or 1,062 kilometers across).

This view looks toward the unilluminated side of the rings from 0.34 degrees below the ring plane. The image was taken in red light with the Cassini spacecraft narrow-angle camera on Sept. 24, 2015.

The image was obtained at a distance of approximately 1.3 million miles (2.1 million kilometers) from Enceladus. Image scale on Enceladus is 7 miles (12 kilometers) per pixel. Tethys was at a distance of 1.6 million miles (2.6 million kilometers) with a pixel scale of 10 miles (16 kilometers) per pixel.

 

[EdwardTivrusky]

No matter how many times i see these kinds of images they still fill me with wonder. Thanks for keeping us up to date.

 

[GulAtiCa]

That is so cool. I love space photos like that.