Cassini Provides Stunning New Looks at Several Moons

Saturn's moon Helene. Credit: NASA//JPL/SSI, image enhanced by Stu Atkinson

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The Cassini spacecraft recently had a mini ‘grand tour’ of several of Saturn’s moons and just sent back some great images of Helene, Mimas, Enceladus and Dione. Above is an amazing view of the Trojan moon Helene, which is only 32 kilometers (20 miles across) and shares an orbit with Dione. Cassini came withing 28,000 km (17,398 miles) of Helene. Thanks to Stu Atkinson for an enhanced version of this raw Cassini image. See one of the original raw images of Helene here.

This image of Saturn's moon Enceladus was obtained by NASA's Cassini spacecraft on Jan. 31, 2011. It shows the famous jets erupting from the south polar terrain of Enceladus. Image credit: NASA/JPL/SSI

Cassini captured several images of the plumes spewing from Enceladus, and other closeup views of the moon’s terrain.

Closeup of Enceladus from approximately 78,015 kilometers away. Credit: NASA/JPL/SSI
This view shows the bright, icy Mimas in front of Saturn's delicate rings. Image credit: NASA/JPL/SSI

A crescent Dione was seen by Cassini on January 29, 2011 from approximately 767,922 kilometers away. Credit: NASA/JPL/SSI

See more of the latest raw images at the Cassini website.

Double Moon Illusion

Enceladus and Dione, as seen by Cassini. Credit: NASA/JPL/Space Science Institute

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We’ve all experienced the Moon Illusion, where our own full Moon looks bigger when seen on the Earth’s horizon. But how about this illusion where you can’t really tell which of these two moons of Saturn is actually bigger, or which is closer, as seen by the Cassini spacecraft? Here, Dione, top right, appears closer to the spacecraft because it is larger than the moon Enceladus, lower left. However, Enceladus was actually closer to Cassini when its visible light, narrow-angle camera took this image.

Dione (1,123 kilometers, or 698 miles, across) is more than twice the size of Enceladus (504 kilometers, or 313 miles, across). The two moons are contrasted with Enceladus’ bright, reflective trailing hemisphere, and Dione’s darker, micrometeor-dusted side, decorated with wispy lighter materials.

Cassini took this image on Dec. 1, 2010 from about 510,000 kilometers (317,000 miles) from Enceladus and approximately 830,000 kilometers (516,000 miles) from Dione. Image scale is 3 kilometers (2 miles) per pixel on Enceladus and 5 kilometers (3 miles) per pixel on Dione.

Source: CICLOPS, the Cassini imaging website

Back-in-Action Cassini Doesn’t Disappoint

Enceladus and Dione line up for the Cassini camera. Credit: NASA/JPL/Space Science Institute

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Here are a few raw images from the Cassini spacecraft’s most recent flyby of Enceladus. The probe seems to be in good health following several weeks in safe mode, after a bit flipped in the command and data subsystem computer. This prevented the spacecraft from registering and following instructions. But she appears to be humming along just fine now, and snapped this great picture of Enceladus and Dione yesterday (have to quote @lukedones on Twitter: “Dione going in the corner pocket!”) Cassini focused on the Enceladus during a close flyby on November 30, so see more below, including a wonderful shot of a veritable curtain of geyser “spray.”

A good look at the spray from the fissures on Enceladus. NASA/JPL/Space Science Institute
Enceladus, backdropped by Saturn's rings. Credit: NASA/JPL/ Space Science Institute.
Closeup of Enceladus. Credit: NASA/JPL/Space Science Institute.
An even closer closeup of Enceladus. Credit: NASA/JPL/Space Science Institute.

See more raw images at the Cassini website, or the CICLOPS imaging website.

Enceladus Fissures Keep Getting Warmer and More Complex

Small water ice particles fly from fissures in the south polar region of Saturn's moon Enceladus in this image taken during the Aug. 13, 2010, flyby of the moon by NASA's Cassini spacecraft. Image credit: NASA/JPL/SSI

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As Cassini scientists await the data from today’s flyby of Enceladus, images and data from August of this year have provided more insight into the active fissures on the icy moon’s south polar region. These geyser-spewing fractures are warmer and more complicated than previously thought.

“The exquisite resolution obtained on one segment of the Damascus fracture — one of the most active regions within the south polar terrain — has revealed a surface temperature reaching a staggering 190 Kelvin, or 120 degrees below zero Fahrenheit,” said Cassini imaging team lead Carolyn Porco, in an email announcing the new images. “Far from the fractures, the temperature of the south polar terrain dips as low as 52 Kelvin, or 365 degrees below zero Fahrenheit.”

Porco said that what this means is that a phenomenal amount of heat is emerging from the fractures which are “undoubtedly the result of the tidal flexing of Enceladus brought about by its orbital resonance with Dione. However, details of this heating process are still unclear and are being studied at this very moment.”

This image shows a high-resolution heat intensity map of part of the south polar region of Saturn's moon Enceladus, made from data obtained by NASA's Cassini spacecraft. Image credit: NASA/JPL/GSFC/SWRI/SSI

The flyby on August 13, 2010 provided infrared spectroscopy along with high resolution images which have enabled scientists to construct the highest-resolution heat intensity maps yet of the hottest part of a region of long fissures spraying water vapor and icy particles from Enceladus. These fissures — known as “tiger stripes,” appear to be laid on in a complex web, and could be connected underground.

Additional high-resolution spectrometer maps of one end of the tiger stripes Alexandria Sulcus and Cairo Sulcus reveal never-before-seen warm fractures that branch off like split ends from the main tiger stripe trenches. They also show an intriguing warm spot isolated from other active surface fissures.

“The ends of the tiger stripes may be the places where the activity is just getting started, or is winding down, so the complex patterns of heat we see there may give us clues to the life cycle of tiger stripes,” said John Spencer, a Cassini team scientist based at Southwest Research Institute in Boulder, Colo.

The temperature measured in this flyby appears slightly higher than previously measured temperatures at Damascus, which were around 170 Kelvin (minus 150 degrees Fahrenheit).

Spencer said he isn’t sure if this tiger stripe is just more active than it was the last time Cassini’s spectrometer scanned it, in 2008, or if the hottest part of the tiger stripe is so narrow that previous scans averaged its temperature out over a larger area. In any case, the new scan had such good resolution, showing details as small as 800 meters (2,600 feet), that scientists could see for the first time warm material flanking the central trench of Damascus, cooling off quickly away from the trench. The Damascus thermal scan also shows large variations in heat output within a few kilometers along the length of the fracture. This unprecedented resolution will help scientists understand how the tiger stripes deliver heat to the surface of Enceladus.

Cassini acquired the thermal map of Damascus simultaneously with a visible-light image where the tiger stripe is lit by sunlight reflecting off Saturn. The visible-light and thermal data were merged to help scientists understand the relationships between physical heat processes and surface geology.

“Our high-resolution images show that this section of Damascus Sulcus is among the most structurally complex and tectonically dynamic of the tiger stripes,” said imaging science team associate Paul Helfenstein of Cornell University, Ithaca, N.Y. Some details in the appearance of the landforms, such as a peculiar pattern of curving striations along the flanks of Damascus, had not previously been noticed in ordinary sunlit images.

ets of water ice particles spew from Saturn's moon Enceladus in this image obtained by NASA's Cassini spacecraft on Aug. 13, 2010. Image credit: NASA/JPL/SSI

The Aug. 13 flyby of Enceladus is the last one dedicated to thermal mapping until 2015 and also gave Cassini its last look at any part of the active south polar region in sunlight.

The flyby today will aid in understanding the interior of the moon through gravity measurements.

To see more images from the August flyby, see Cassini website, and the CICLOPS imaging site.

Source: JPL, Porco email

Upcoming Flybys Could Provide Clues to Interior of Enceladus

At least four distinct plumes of water ice spew out from the south polar region of Saturn's moon Enceladus. Credit: NASA/JPL/Space Science Institute

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What is going on inside Saturn’s moon Enceladus and what powers the icy geysers and jets? A pair of upcoming flybys by the Cassini spacecraft could help answer those questions. Radio instruments on board will measure the gravity field of Enceladus and focus particularly on the very intriguing south polar hot spot.

Of course, the success of these flybys hinges on the Cassini mission controllers being able to wake up the dormant spacecraft which has been in safe mode since November 2. Teams will attempt to get Cassini up and running again tomorrow, November 24, and they don’t anticipate any problems.


Cassini went into the protective standby mode and the likely cause of the problem was a faulty program code line, or a flipped bit in the spacecraft’s command and data system computer.

The upcoming flybys of Enceladus will put Cassini very close – about 48 kilometers (30 miles) above the surface. The first will take place on November 30. Pairing this flyby with one on April 28, should provide scientists enough information to determine the nature of the interior right under the hot spot. The next flyby on December 21, Cassini will make 50-kilometer pass over the north pole of Enceladus. The fields and particles instruments will be trying to “sniff” anything coming from the moon.

There will be two three-hour “wing” observations before and after closest-approach (from five to eight hours from closest approach on either side), and then three more hours centered directly around closest approach. The Cassini team is throwing almost the entire gamut of instruments into the flyby program, between radio science (RSS) observations, the imaging science system (ISS) and composite infrared spectrometer (CIRS) which will observe this moon on the inbound leg, and CIRS and the visible and infrared mapping spectrometer (VIMS) which will take data on the outbound leg, with other optical remote sensing and fields, particles and waves instruments also taking data.

Source: Cassini

Warm ‘Perrier’ Ocean Could be Powering Enceladus’ Geysers

Proposed 'Perrier' Ocean for Enceladus. Credit: NASA/JPL/Space Science Institute

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Bottled water companies take note: an exotic form of warm, bubbly mineral water could be what feeds the mysterious jets spraying from the south polar region of Saturn’s moon Enceladus. A new model of the sub-surface ocean explains how the small moon could be so cryo-volcanically active. The Cassini spacecraft has detected sodium and potassium salts, as well as carbonates in the water vapor plumes spewing from the moon, which indicates a liquid, bubbly subsurface ocean. “There is a plume chamber, where some of the bubbles can pop the cap of the thin ice crust, and through that process is how the plumes get sprayed out,” said Dennis Matson, a NASA planetary scientist from JPL, speaking at a press briefing at the American Astronomical Society’s Division for Planetary Sciences meeting in Pasadena, California.

The schematic image (top) is laid on top of a picture of the Enceladus jets taken by Cassini’s imaging cameras in November 2009. It shows bubbles in subsurface seawater traveling through a passage in the ice crust to feed a geyser. The water flows back down to the subsurface ocean through cracks in the ice.

Matson explained the process:

“What we think is going on is that Enceladus has a subsurface ocean where water, heat and chemicals are stored before they erupt,” he said. There is an ice crust, many tens of kilometers thick. The ocean is gas rich, — and previous researchers dubbed such an ocean as a ‘Perrier’ ocean -– which basically “pops the cap” of the ice crust.

“What is happening is that water comes up and pressure is released,” said Matson. “Gases and water come out and the bubbles come near the surface and supply materials to the plumes. Water also transfers laterally, to a great extent, from the point of the plumes. This transfers heat to the surface, by analogy, like the radiator on your car. You have water coming out, which transfers heat to the thin ice layer, and then the heat is radiated to space. Cooled water goes down through cracks in the ice where it gets ready for another trip to the surface. “

This image compares heat flow at Earth and Saturn’s moon Enceladus. Credit: NASA/JPL

Cassini also found an impressive amount of heat flow over a small area coming from Enceladus’ interior. About four years ago, Cassini’s composite infrared spectrometer instrument detected a heat flow in the south polar region of at least 6 gigawatts, the equivalent of at least a dozen electric power plants. This is at least three times as much heat as an average region of Earth of similar area would produce, despite Enceladus’ small size.

“To put the heat flow in perspective,” said Matson, “the heat flow for the Earth has 87 of these units, but on the south pole of Enceladus, 250 units. At Yellowstone, there are 2500 units, but at one of the tiger stripe hots spots on Enceladus, we find heat flow as big as 13,000 units.”

The heat is, of course, relative to the surrounding environment. The subsurface bubbly water is probably just below freezing, which is 273 degrees Kelvin or 32 degrees Farenheit, whereas the surface is a frigid 80 degrees Kelvin or -316 degrees Farenheit. However, Matson said they have also seen surface temperatures as high as 180 K, when only 70 K was expected at the south pole.

Cassini imaging scientists used views like this one to help them identify the source locations for individual jets spurting ice particles, water vapor and trace organic compounds from the surface of Saturn's moon Enceladus. Credit: NASA

Finding the sodium in the icy grains in the plume is huge piece of evidence pointing to a subsurface ocean. Previously, Earth-based observations did not detect salts in the plume, and so scientists didn’t think a liquid ocean was possible. But infrared observations with an instrument on Cassini found the particles in the plumes include water ice, and substantial amounts of sodium and potassium salts and carbonates, as well as organics.

“The sodium was hiding in the little grains,” Matson said. “In the case of Enceladus, sodium isn’t in the vapor, it’s in the solid particles. This was something entirely new that had not been seen elsewhere.”

Also new is that the heat from Enceladus appears to be originating in the ocean, and also the realization there is a circulation system inside the moon, where there is process of pumping the water to the surface.

“This process we’ve outlined, where getting the water up to the surface, you have the heat, the water, and sodium and potassium all from one source that brings that up to the surface. So you have one process that delivers all those things, whereas before we had separate processes to try and explain each of them.”

Source: DPS press briefing

Simply Astonishing: Enceladus, the Jet-Powered Moon

The plumes of Enceladus are highlighted in this Cassini image. Credit: NASA/JPL/Space Science Institute

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What an astonishing view of Saturn’s moon Enceladus, as seen by Cassini! At least four different plumes of water ice are spewing out from the south polar region, highlighted because of the black space behind the Moon. On Twitter, Carolyn Porco said that we see four jets because we’re looking down the four tiger stripe fractures crossing the south pole. “How lovely it is to know!” she added.

Cassini was about 617,000 kilometers (383,000 miles) away from Enceladus when it captured this image.

More info: Cassini website

Amazing New Close-up Images of Enceladus

Caption: Looking down at a plume on Enceladus. Credit: NASA/Space Science Science Institute.

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Oh, wow! This is one of the best images yet from the Cassini spacecraft of the “tiger stripes” in the south polar region of Saturn’s moon Enceladus. Over the weekend, Cassini flew by Enceladus, and has sent back some incredible new images, such as the one above. The tiger stripes are actually giant fissures that spew jets of water vapor and organic particles hundreds of kilometers, or miles, out into space, and here, Cassini is staring right down into one of the fissures. See more great images of Enceladus below, plus images of the moons Dione and Tethys.


Close-up of the cracked, crevassed surface of Enceladus. Credit: NASA/Space Science Institute.

While the winter is darkening the moon’s southern hemisphere, Cassini has its own version of “night vision goggles” — the composite infrared spectrometer instrument – to track heat even when visible light is low. It will take time for scientists to assemble the data into temperature maps of the fissures.

Enceladus against Saturn's limb. Credit: NASA/Space Science Institute.
More plumes on Enceladus. Credit: NASA/Space Science Institute.
Close-up of Tethys. Credit: NASA/Space Science Institute

Dione from 115,370 kilometers away. Credit: NASA/Space Science Institute

See more amazing images from Cassini’s latest at the CICLOPS website.

Emily Lakdawalla at the Planetary Blog also has created some very cool movies from the flyby images.


Hat tip to Stu Atkinson

Incredible Images of Enceladus From Cassini’s Latest Flyby

Titan, Saturn's rings and Enceladus. Credit: NASA/JPL/SSI

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Wow. Cassini the artist has struck again, this time with amazing images from the close flyby of Enceladus that we wrote a preview about earlier this week. Cassini flew by Enceladus during the early hours of May 18 UTC, coming within about 435 kilometers (270 miles) of the moon’s surface. The raw images came in late last night, and in my inbox this morning was an email from Stuart Atkinson, (no relation, but great name) alerting me to the treasures. Stu himself has called this image “the new iconic image of the space age,” and Emily Lakdawalla of the Planetary Blog has called these images “some of the most amazing Cassini has captured yet.”

What you’re seeing here is hazy Titan, backlit by the Sun, with Saturn’s rings in the foreground– plus, at the way bottom is the limb of the night side of Enceladus’ south pole. Emily has created a flipped, annotated image (plus there’s more Enceladus jaw-droppers below:

nceladus, Titan, and the rings of Saturn (explained) Credit: NASA/JPL/SSI/annotated by Emily Lakdawa. Click for larger version.

The 'fountains' of Enceladus. Credit: NASA/JPL/SSI

Three huge “fountains” of Enceladus geysers are visible in this raw image taken by Cassini on May 18, 2010. The camera was pointing toward Enceladus at approximately 14,972 kilometers away, and the image was taken using the CL1 and CL2 filters. Emily, with her photo editing prowess, has created a movie from four different images as Cassini cruised closer to the moon.

Astro0 on UnmannedSpaceflight.com has put the two different images together to create a collage of what it would have looked like if the plumes were visible in the image with Titan. Gorgeous! Plus, here’s a color version Astro0 created.

Plus there’s this very interesting raw image from Cassini:

Raw image from Cassini on May 18. Credit: NASA/JPL/SSI

Explanations anyone?

Cassini will be flying by Titan in the early hours of May 20 UTC, coming within 1,400 kilometers (750 miles) of the surface. Although Cassini will primarily be doing radio science during this pass to detect subtle variations in the gravitational tug on the spacecraft by Titan, hopefully we’ll see some new visible light images of Titan, as well.

For more images from Cassini, see the Cassini website, and the section for the raw images.