Cassini Archives

May 4, 2012December 23, 2015 by Jason Major

Exploration at its Finest: Cassini Visits Dione

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After completing its most recent flyby of Enceladus, Cassini made a pass by Dione — its final visit of the icy moon for the next three years. Coming within 5,000 miles (8000 km) of Dione on May 2, Cassini captured some fantastic images of the moon’s heavily-cratered and frozen surface. Here’s just a few of the raw images that arrived back here on Earth earlier today:

W00074059 — Crescent-lit Dione, with some reflected light via Saturnshine

W00074064 — A nearly fully-lit Dione, with Saturn's rings in the background

N00186325 — Dione's extensively-cratered limb

N00186448 — Some of Dione's signature "wispy lines", bright icy faces of sheer cliffs now known to be tectonic in origin

Dione 5-2-12b IR-G-UV — A color-composite image of an ancient impact crater on the edge of Dione's Saturn-facing side - this could be from the impact that spun the moon 180 degrees. (NASA/JPL/SSI/J. Major)

698 miles (1123 km) in diameter, Dione orbits Saturn at about the same distance that the Moon orbits Earth. Its composition is two-thirds water ice, which at the incredibly cold temperatures found around Saturn behaves like rock does here on Earth.

Cassini won’t visit Dione so closely again until June 2015, after spending three years angled high out of the equatorial plane while it studies Saturn’s rings and polar regions.

As Carolyn Porco, Cassini Imaging Team Leader said today, “This is exploration at its finest. It won’t continue forever. So, enjoy it while it lasts!”

See more on the Cassini Imaging Central Laboratory for Operations (CICLOPS) site here.

Image credits: NASA/JPL/Space Science Institute

May 3, 2012December 23, 2015 by Jason Major

Enceladus On Display In Newest Images From Cassini

Enceladus' southern ice geysers are brilliant in backlit sunlight (NASA/JPL/SSI/J. Major)

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The latest images are in from Saturn’s very own personal paparazzi, NASA’s Cassini spacecraft, fresh from its early morning flyby of the ice-spewing moon Enceladus. And, being its last closeup for the next three years, the little moon didn’t disappoint!

The image above is a composite I made from two raw images (this one and this one) assembled to show Enceladus in its crescent-lit entirety with jets in full force. The images were rotated to orient the moon’s southern pole — where the jets originate — toward the bottom.

Cassini was between 72,090 miles (116,000 km) and 90,000 miles (140,000 km) from Enceladus when these images were acquired.

This morning’s E-19 flyby completed a trio of recent close passes by Cassini of the 318-mile (511-km) -wide moon, bringing the spacecraft as low as 46 miles (74 km) above its frozen surface. The goal of the maneuver was to gather data about Enceladus’ internal mass — particularly in the region around its southern pole, where a reservoir of liquid water is thought to reside — and also to look for “hot spots” on its surface that would give more information about its overall energy distribution.

Cassini had previously discovered that Enceladus radiates a surprising amount of heat from its surface, mostly along the “tiger stripe” features — long, deep furrows (sulcae) that gouge its southern hemisphere, they are the source of the water-ice geysers.

Cassini also used the flyby opportunity to study Enceladus’ gravitational field.

By imaging the moon with backlit lighting from the Sun the highly-reflective ice particles in the jets become visible. More direct lighting reduces the jets’ visibility in images, which must be exposed for the natural light of the scene or risk “blowing out” due to Enceladus’ natural high reflectivity.

The images below are raw spacecraft downloads right from the Cassini’s imaging headquarters in Boulder, CO.

N00186286 — Enceladus' geysers in action on May 2, 2012. (NASA/JPL/SSI)

W00074053 — Enceladus sprays ice into the hazy E ring, which orbits Saturn (NASA/JPL/SSI)

Cassini also swung closely by Dione during this morning’s flyby but the images from that encounter aren’t available yet. Stay tuned to Universe Today for more postcards from Saturn!

As always, you can follow along with the ongoing Cassini mission on JPL’s dedicated site here, as well as on the Cassini Imaging Central Laboratory for Operations (CICLOPS) site.

May 1, 2012December 23, 2015 by Nancy Atkinson

Cassini’s Last Flyby of Enceladus Until 2015

Below a darkened Enceladus, a plume of water ice is backlit in this view. Credit: NASA/JPL-Caltech/Space Science Institute

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On May 2, the Cassini spacecraft will be swooping past the moon we all love to love — Enceladus — and coming within 74 kilometers (46 miles) of its fractured, jet-spewing surface. The images should be spectacular, and the science should be just as enticing. With Cassini’s radio science experiment, scientists hope to learn more about how mass is distributed under Enceladus’ south polar region, the very interesting place which features jets of water ice, water vapor and organic compounds spraying out of long fractures.

This is the last close flyby of Enceladus until 2015, so we have to take advantage of the views!

Cassini scientists will be looking specifically for a concentration of mass in that region could indicate subsurface liquid water or an intrusion of warmer-than-average ice that might explain the unusual plume activity. They’ll also be observing the plumes and looking for hot spots to try and understand the global energy balance of Enceladus.

They also hope to learn more about the moon’s internal structure by measuring variations in the gravitational pull of Enceladus against the steady radio link to NASA’s Deep Space Network on Earth.

Additionally, Cassini’s composite infrared spectrometer instrument will be observing the side of Enceladus that always faces away from Saturn to monitor for hot spots. The imaging camera team also plans to take images of the plume to look for variability in the jets.

Cassini will also be flying by Dione at a distance of about 8,000 kilometers (5,000 miles), enabling the imaging cameras to create several mosaic images of the icy moon, and the composite infrared spectrometer to monitor heat emission.

We’ll try to post images and info as they become available!

April 27, 2012December 23, 2015 by Jason Major

Cassini Exposes Phoebe As More Planet Than Moon

Color-composite image of Phoebe as seen by Cassini in 2009.

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Saturn’s curious moon Phoebe features a heavily-cratered shape and orbits the ringed planet backwards at a considerable distance of over 8 million miles (12.8 million km). According to recent news from the Cassini mission Phoebe may actually be a Kuiper Belt object, having more in common with planets than it does with any of Saturn’s other satellites.

132 miles (212 km) in diameter, Phoebe is the largest of Saturn’s irregular moons — a cloud of small, rocky worlds held in distant orbits at highly inclined paths. Its backwards (retrograde) motion around Saturn and dense composition are dead giveaways that it didn’t form in situ within the Saturnian system, but rather was captured at some point when it strayed too close to the gas giant.

In fact it’s now thought that Phoebe may be a remnant from the formation of the Solar System — a planetesimal — with its own unique history predating its adoption into Saturn’s extended family of moons.

“Unlike primitive bodies such as comets, Phoebe appears to have actively evolved for a time before it stalled out,” said Julie Castillo-Rogez, a planetary scientist at NASA’s Jet Propulsion Laboratory. “Objects like Phoebe are thought to have condensed very quickly. Hence, they represent building blocks of planets. They give scientists clues about what conditions were like around the time of the birth of planets and their moons.”

Although Phoebe is heavily eroded and irregularly-shaped today at one time it may have been much rounder. But an early composition of radioactive elements would have generated heat, and as it warmed it “deflated” through compression, growing denser and denser.

640120main_pia15507-43_800-600 — Map of Phoebe's surface. (NASA/JPL-Caltech/SSI/Cornel)

Now, Phoebe exhibits a similar density to Pluto — another denizen of the Kuiper Belt.

At some point Phoebe may even have had water, kept liquid by its radioactive heat. That is, until the heat faded and it froze, creating the icy surface detected by Cassini’s instruments.

Still, Cassini’s study of Saturn’s moons has provided scientists with clues to what was happening much earlier on in the Solar System. What caused Phoebe to drift inwards to be caught up in orbit around Saturn? How did it survive such a supposed shuffling of planets and other worlds did not? As Cassini continues its investigation answers — and undoubtedly even more questions — will be uncovered.

Read more on NASA’s news release here.

Image: NASA/JPL/SSI. Color composition by Gordan Ugarkovic.

April 23, 2012December 23, 2015 by Nancy Atkinson

Glittering ‘Mini-Jets’ Found in Saturn’s Curious F-Ring

This set of six images obtained by NASA's Cassini spacecraft shows trails that were dragged out from Saturn's F ring by objects about a half mile (1 kilometer) in diameter. Scientists have seen more than 500 of these kinds of trails in over 20,000 images collected by Cassini from 2004 to 2011. Credit: NASA/JPL-Caltech/Space Science Institute

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New images from the Cassini spacecraft have revealed kilometer-sized objects piercing through parts of Saturn’s F ring, leaving glittering trails behind them. These trails in the rings, which scientists are calling “mini-jets,” provide insight into the curious behavior of the F ring, which Cassini imaging team leader Carolyn Porco called “Saturn’s most beguiling phenomena.” With new detailed images, Cassini reveals the intricate workings of the F ring and hordes of tiny moonlet companions creating the trails.

“I think the F ring is Saturn’s weirdest ring, and these latest Cassini results go to show how the F ring is even more dynamic than we ever thought,” said Carl Murray, a Cassini imaging team member from Queen Mary University of London, England. “These findings show us that the F ring region is like a bustling zoo of objects from a half mile [kilometer] in size to moons like Prometheus a hundred miles [kilometers] in size, creating a spectacular show.”

f-ring-full — Images from NASA's Cassini spacecraft have revealed half-mile-sized (kilometer-sized) objects punching through parts of Saturn's F ring, leaving glittering trails behind them. Credit: NASA/JPL-Caltech/Space Science Institute

Scientists have known that relatively large objects like Prometheus (as long as 92 miles, or 148 kilometers, across) can create channels, ripples and snowballs in the F ring. But scientists didn’t know what happened to these snowballs after they were created, Murray said. Some were surely broken up by collisions or tidal forces in their orbit around Saturn, but now scientists have evidence that some of the smaller ones survive, and their differing orbits mean they go on to strike through the F ring on their own.

PIA15502 — This image obtained by NASA's Cassini spacecraft around the time it went into orbit around Saturn in 2004 shows a short trail of icy particles dragged out from Saturn's F ring. Credit: NASA/JPL-Caltech/Space Science Institute

These small objects appear to collide with the F ring at gentle speeds – something on the order of about 4 mph (2 meters per second). The collisions drag glittering ice particles out of the F ring with them, leaving a trail typically 20 to 110 miles (40 to 180 kilometers) long. Murray’s group happened to see a tiny trail in an image from Jan. 30, 2009 and tracked it over eight hours. The long footage confirmed the small object originated in the F ring, so they went back through the Cassini image catalog to see if the phenomenon was frequent.

“The F ring has a circumference of 550,000 miles [881,000 kilometers], and these mini-jets are so tiny they took quite a bit of time and serendipity to find,” said Nick Attree, a Cassini imaging associate at Queen Mary. “We combed through 20,000 images and were delighted to find 500 examples of these rogues during just the seven years Cassini has been at Saturn.”

In some cases, the objects traveled in packs, creating mini-jets that looked quite exotic, like the barb of a harpoon. Other new images show grand views of the entire F ring, showing the swirls and eddies that ripple around the ring from all the different kinds of objects moving through and around it.

“Beyond just showing us the strange beauty of the F ring, Cassini’s studies of this ring help us understand the activity that occurs when solar systems evolve out of dusty disks that are similar to, but obviously much grander than, the disk we see around Saturn,” said Linda Spilker, Cassini project scientist based at NASA’s Jet Propulsion Laboratory, Pasadena, Calif. “We can’t wait to see what else Cassini will show us in Saturn’s rings.”

See more images and animations at the CICLOPS website.

Source: JPL

April 19, 2012December 23, 2015 by Jason Major

African Lake Has a Twin on Titan

Titan's Ontario Lacus is found to bear a striking resemblance to Namibia's Etosha Pan. (NASA/JPL/ESA)

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A large lake on Saturn’s cloud-covered Titan seems very similar to the Etosha Pan, a salt-encrusted dry lakebed in northern Namibia that periodically fills with water. As it turns out, Titan’s “great lake” may also be temporary.

Ontario Lacus, so named because of its similarity both in shape and size to Lake Ontario here on Earth, was first discovered near the south pole of Titan by the Cassini spacecraft in 2009. Its smooth, dark appearance in radar images indicated a uniform and reflective surface, implying a large — although likely shallow — body of liquid.

Of course, on Titan the liquid isn’t water — it’s methane, which is the main ingredient of the hydrologic cycle found on the giant moon. That far from the Sun the temperatures at Titan’s poles fall to a frigid -300ºF (-185ºC), much too cold for water to exist as a liquid and so, on this world, methane has taken its place.

A research team led by Thomas Cornet of the Université de Nantes, France has taken a closer look at Cassini’s radar data of Ontario Lacus and found evidence of channels carved into the southern portion. According to the team, this likely indicates that the lakebed surface is exposed.

dn17665-1_500 — Cassini image of Ontario Lacus. (NASA/JPL/SSI)

“We conclude that the solid floor of Ontario Lacus is most probably exposed in those areas,” said Cornet.

In addition, sediment layers surrounding the lake suggest that the liquid level has varied.

All in all, this reveals a striking resemblance between Ontario Lacus and Namibia’s Etosha Pan — an “ephemeral lake” that is dry for much of the year, occasionally filling with a shallow layer of water which evaporates, leaving salty rings of sediment.

The inherent otherworldly nature of Etosha Pan is further underlined — and perhaps foreshadowed! — by its use as a backdrop in the 1968 sci-fi film 2001: A Space Odyssey.

Although Ontario Lacus was initially thought to be permanently filled with liquid hydrocarbons, the team’s findings draw a strong correlation with this well-known Earthly environment, suggesting a much more temporary nature and showing the value of comparative research.

20120415-namibia2-full — Satellite image of Etosha Pan, acquired on April 28, 2012. (Chelys/EOSnap)

“These results emphasise the importance of comparative planetology in modern planetary sciences,” said Nicolas Altobelli, Cassini project scientist for ESA.”Finding familiar geological features on alien worlds like Titan allows us to test the theories explaining their formation.”

Read the press release from ESA here.

Image credits: Cassini radar image JPL/NASA. Envisat radar image ESA. Composite image: LPGNantes.

April 16, 2012December 23, 2015 by Jason Major

Cassini Slips Through Enceladus’ Spray

Cassini's latest view of Enceladus' icy spray, acquired on April 14, 2012.

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Spray it again, Enceladus! This Saturday the Cassini spacecraft paid another visit to Enceladus, Saturn’s 318-mile-wide moon that’s become famous for its icy geysers.During its latest close pass Cassini got a chance to “taste” Enceladus’ spray using its ion and neutral mass spectrometer, giving researchers more information on what sort of watery environment may be hiding under its frozen, wrinkled surface.

The image above shows a diagonal view of Enceladus as seen from the night side. (The moon’s south pole is aimed at a 45-degree angle to the upper right.) Only by imaging the moon backlit by the Sun can the geysers of fine, icy particles be so well seen.

During the flyby Cassini passed within 46 miles (74 km) of Enceladus’ surface.

This image was captured during the closest approach, revealing the distressed terrain of Enceladus’ south pole. Although a bit blurry due to the motion of the spacecraft, boulders can be made out resting along the tops of high , frozen ridges. (Edited from the original raw image to enhance detail.)

W00073473 (edit) — Enceladus' southern fissures, the source of its spray. (NASA/JPL/SSI/J. Major)

This flyby occurred less than three weeks after Cassini’s previous visit to Enceladus. Why pay so much attention to one little moon?

Basically, it’s the one place in our solar system that we know of where a world is spraying its “habitable zone” out into space for us to sample.

“More than 90 jets of all sizes near Enceladus’s south pole are spraying water vapor, icy particles, and organic compounds all over the place,” said Carolyn Porco, planetary scientist and Cassini Imaging science team leader, during a NASA interview in March. “Cassini has flown several times now through this spray and has tasted it. And we have found that aside from water and organic material, there is salt in the icy particles. The salinity is the same as that of Earth’s oceans.

“In the end, it’s the most promising place I know of for an astrobiology search,” said Porco. (Read the full interview here.)

N00185749 — A crescent-lit Enceladus sprays its "habitable zone" out into space.

Not to be left out, Tethys was also paid a visit by Cassini. The 662-mile-wide moon boasts one of the most extensively cratered surfaces in the Solar System, tied with its sister moons Rhea and Dione. In this raw image captured by Cassini on April 14, we can see some of the moon’s ancient, larger craters, including Melanthius with its enormous central peak.

tethys-4-14-12-melanthius — Saturn's moon Tethys, imaged by Cassini on April 14, 2012.

Cassini passed Tethys at a distance of about 6,000 miles (9000 km) after departing Enceladus. Cassini’s composite infrared spectrometer looked for patterns in Tethys’ thermal signature while other instruments studied the moon’s geology.

Image credits: NASA/JPL/Space Science Institute. See more images from the Cassini mission on the CICLOPS site here.

March 30, 2012December 23, 2015 by Jason Major

Postcards From Saturn

Saturn's second-largest moon Rhea, in front of the rings and a blurred Epimetheus (or Janus) whizzing behind. Acquired March 29, 2012.

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Over the past few days NASA’s Cassini spacecraft has performed flybys of several of Saturn’s moons. From the ostentatious Enceladus with its icy geysers to the rugged relief of Rhea, the sharp peaks of Dione’s frigid craters and even diminutive Janus, Cassini has once again returned a stack of stunning views from the Saturnian system, nearly 815 million miles from home.

Check out some of the images, and wish you were there!

N00185316 — 110-mile (177-km) -wide Janus in front of Saturn's night side.

N00185283 — A crescent-lit Enceladus shows off its jets. (South is up.)

N00185291 — Enceladus' fractured surface is some of the most reflective terrain in the Solar System.

Rhea Mimas 3-29-12 — Wide-angle view of Rhea, Saturn and Mimas

And here’s a color-composite of Janus I assembled from three raw images taken in ultraviolet, green and infrared color channels. The results were tweaked to make it a little more true-color as what we might see with our limited human vision:

Janus 3-27-12 — Color composite of Janus in front of Saturn, made from raw images taken in UV, green and IR color filters. (NASA/JPL/SSI/J. Major)

“Though we’ve been in orbit around Saturn for nearly 8 years now, we still continue to image these moons for mapping purposes and, in the case of Enceladus, to learn as much as we can about its famous jets and the subterranean, organic-rich, salty, liquid water chamber from which we believe they erupt.”

– Carolyn Porco, Cassini Imaging Team leader

For more images from Cassini, check out JPL’s mission site and the CICLOPS imaging lab site here.

Image credits: NASA/JPL/Space Science Institute.

March 28, 2012December 23, 2015 by Jason Major

“Snowing Microbes” On Saturn’s Moon?

Cassini image of Enceladus from Dec. 2010 (NASA/JPL/SSI)

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Enceladus, Saturn’s 318-mile-wide moon that’s become famous for its ice-spraying southern jets, is on astronomers’ short list of places in our own solar system where extraterrestrial life could be hiding — and NASA’s Cassini spacecraft is in just the right place to try and sniff it out.

On March 27, Cassini came within 46 miles (74 km) of Enceladus’ south pole, the region where the moon’s many active water-ice jets originate from. This was Cassini’s closest pass yet over the southern pole, allowing the spacecraft to use its ion and neutral mass spectrometer — as well as its plasma spectrometer, recently returned to service — to taste the icy spray emanating from deep fissures called “tiger stripes” that scar Enceladus’ surface.

(Fly along with Cassini toward Enceladus’ jets here.)

“More than 90 jets of all sizes near Enceladus’s south pole are spraying water vapor, icy particles, and organic compounds all over the place,” said Carolyn Porco, planetary scientist and Cassini Imaging science team leader. “Cassini has flown several times now through this spray and has tasted it. And we have found that aside from water and organic material, there is salt in the icy particles. The salinity is the same as that of Earth’s oceans.”

In addition to water, salt and organics, there is also a surprising amount of heat — heat generated in part by tidal friction, helping keep Enceladus’ underground water reserves liquid.

“If you add up all the heat, 16 gigawatts of thermal energy are coming out of those cracks,” Porco said.

This creates, in effect, a so-called “Goldilocks zone” of potential habitability orbiting around Saturn… a zone that Cassini has easy access to.

“It’s erupting out into space where we can sample it. It sounds crazy but it could be snowing microbes on the surface of this little world,” Porco said. “In the end, it’s the most promising place I know of for an astrobiology search. We don’t even need to go scratching around on the surface. We can fly through the plume and sample it. Or we can land on the surface, look up and stick our tongues out. And voilà…we have what we came for.”

enceladus_stripe_11-30-10-1 — Cassini's view down into a jetting "tiger stripe" in August 2010

Cassini’s latest results — and images! — from the flyby should be landing on Earth any time now. Stay tuned to Universe Today for more updates on Cassini and Enceladus.

Massive Ice Avalanches on Iapetus

Long-runout landslides on Iapetus: A) Malun crater blocky landslide; B) Multiple lobate landslide in Engelier Basin; C) Lobate landslide in Gerin Basin. Credit: McKinnon et. al, LPSC, 2012.

We’ve seen avalanches on Mars, but now scientists have found avalanches taking place on an unlikely place in our solar system: Saturn’s walnut-shaped, two-toned moon Iapetus. And these aren’t just run-of-the-mill avalanches: they are huge inundations of debris. These events are specifically known as long-runout landslides — debris flows that have traveled unusually long distances. Just how these avalanches are occurring is somewhat of a mystery, according to Bill McKinnon from Washington University in St. Louis.

“This is really about the mystery of long-runout landslides, and no one really knows for sure what causes them,” said McKinnon, speaking at the Lunar and Planetary Science Conference this week.

These avalanches or landslides certainly have their Earthly counterparts and, as noted, similar events are found on Mars, where they are especially associated with the steep canyon walls of the Valles Marineris system. However, the large mass movements on Iapetus in the form of long-runout landslides are less common.

McKinnon said the amount of material that has been moved in all the avalanches on Iapetus that he and his team have found exceeds all the material moved in known Martian landslides (in published data), even though Mars is much bigger than Iapaetus.

“The mechanics of long-runout landslides are poorly understood, and mechanisms proposed for friction reduction are so numerous I can’t fit them all on one Powerpoint slide,” McKinnon said during his talk. Possible explanations include water (such as released groundwater), wet or saturated soil, ice, trapped or compressed air, acoustic fluidization, and more.

On Iapetus there is obviously no water or atmosphere to create conducive conditions for avalanches. But McKinnon and his team have identified over two dozen avalanche events as seen in images from the Cassini spacecraft.

Many of the landslides are seen from crater and basin walls and steep scarps. McKinnon and his team have found two types of avalanches: ‘blocky’ with rough-looking debris and smoother lobate landslides. They also see evidence that over time, multiple avalanches have likely occurred in the same location, so Iapetus must have a long history of mass wasting and landslides.

So, what allows for the huge avalanches on Iapetus? McKinnon said ice provides the best answer to that question. The low density of Iapetus indicates that it is mostly composed of ice, with only about 20% of rocky materials.

“There seems to be a necessity for a fluidization or liquid mechanism,” McKinnon said. “If ice is warmed just enough it will become slippery,” reducing the friction and cohesiveness of the crater or basin wall.

What they are seeing, especially in the lobate landslides, is consistent with ‘rheological’ flow similar to molten lava or fluid mudslides.

So, ice rubble within the rocky faces of crater and basin walls are heated just enough – either by flash heating or friction — that the surfaces become slippery. “The energetics are favorable for this mechanism on Iapetus,” McKinnon said.

Iapetus has a very slow rotation, longer than 79 days, and such a slow rotation means that the daily temperature cycle is very long — so long that the dark material can absorb heat from the Sun and warm up. Of course the dark part of Iapetus absorbs more heat than the bright icy material; therefore, McKinnon said, this is all fairly enigmatic.

Plus, saying that it “warms up” on Iapetus is a bit of an overstatement. Temperatures on the dark region’s surface are estimated to reach 130 K (-143 °C; -226 °F) at the equator and temperatures in the brighter area only reach about 100 K (-173 °C; -280 °F).

Whatever the mechanisms, the long-runout landslides on Iapetus are fairly unique when it comes to icy planetary bodies. McKinnon referenced that just two mass movements of modest scale have been detected on Callisto, and there is limited evidence of similar events on Phoebe.

These ice avalanches certainly deserve more investigation on a moon which McKinnon described as having “singularly spectacular topography,” and additional research and a more detailed paper are forthcoming.

Read the LPSC abstract: Massive Ice Avalanches on Iapetus, and the Mechanism of Friction Reduction in Long-Runout Landslides