Cassini Archives

December 17, 2009December 24, 2015 by Nancy Atkinson

Cassini Captures Sunshine Gleaming off Lake on Titan

This image shows the first flash of sunlight reflected off a lake on Saturn’s moon Titan. Credit: NASA/JPL

Dear friend,
Ah, yes. Another gorgeous day here in the northern lake district. It warmed up to about 94 K (-179 °C, or -290 °F) and we sat and enjoyed the sunshine gleaming off the liquid lakes here on Titan. Wish you were here!

Liquid lakes? Gleaming sunshine? Titan?

Yes, it’s all true. The Cassini Spacecraft has captured the first flash of sunlight reflected off a lake on Saturn’s moon Titan, confirming the presence of liquid on the part of the moon dotted with many large, lake-shaped basins.

Cassini scientists had been looking for the glint, also known as a specular reflection, since the spacecraft began orbiting Saturn in 2004. But Titan’s northern hemisphere, which has more lakes than the southern hemisphere, has been veiled in winter darkness. The sun only began to directly illuminate the northern lakes recently as it approached the equinox of August 2008, the start of spring in the northern hemisphere. Titan’s hazy atmosphere also blocked out reflections of sunlight in most wavelengths. This serendipitous image was captured on July 8, 2009, using Cassini’s visual and infrared mapping spectrometer.

This image is being presented at the fall meeting of the American Geophysical Union in San Francisco.

“This one image communicates so much about Titan — thick atmosphere, surface lakes and an otherworldliness,” said Bob Pappalardo, Cassini project scientist, based at NASA’s Jet Propulsion Laboratory, Pasadena, Calif. “It’s an unsettling combination of strangeness yet similarity to Earth. This picture is one of Cassini’s iconic images.”

Titan, Saturn’s largest moon, has captivated scientists because of its many similarities to Earth. Scientists have theorized for 20 years that Titan’s cold surface hosts seas or lakes of liquid hydrocarbons, making it the only other planetary body besides Earth believed to harbor liquid on its surface. While data from Cassini have not indicated any vast seas, they have revealed large lakes near Titan’s north and south poles.

In 2008, Cassini scientists using infrared data confirmed the presence of liquid in Ontario Lacus, the largest lake in Titan’s southern hemisphere. But they were still looking for the smoking gun to confirm liquid in the northern hemisphere, where lakes are also larger.

Katrin Stephan, of the German Aerospace Center (DLR) in Berlin, an associate member of the Cassini visual and infrared mapping spectrometer team, was processing the initial image and was the first to see the glint on July 10th.

“I was instantly excited because the glint reminded me of an image of our own planet taken from orbit around Earth, showing a reflection of sunlight on an ocean,” Stephan said. “But we also had to do more work to make sure the glint we were seeing wasn’t lightning or an erupting volcano.”

Team members at the University of Arizona, Tucson, processed the image further, and scientists were able to compare the new image to radar and near-infrared-light images acquired from 2006 to 2008.

They were able to correlate the reflection to the southern shoreline of a lake called Kraken Mare. The sprawling Kraken Mare covers about 400,000 square kilometers (150,000 square miles), an area larger than the Caspian Sea, the largest lake on Earth. It is located around 71 degrees north latitude and 337 degrees west latitude.

The finding shows that the shoreline of Kraken Mare has been stable over the last three years and that Titan has an ongoing hydrological cycle that brings liquids to the surface, said Ralf Jaumann, a visual and infrared mapping spectrometer team member who leads the scientists at the DLR who work on Cassini. Of course, in this case, the liquid in the hydrological cycle is methane rather than water, as it is on Earth.

“These results remind us how unique Titan is in the solar system,” Jaumann said. “But they also show us that liquid has a universal power to shape geological surfaces in the same way, no matter what the liquid is.”

Source: JPL

December 9, 2009December 24, 2015 by Nancy Atkinson

Saturn’s Hexagon Endures!

This movie from Cassini, made possible only as Saturn’s north pole emerged from winter darkness, shows new details of a jet stream that follows a hexagon-shaped path and has long puzzled scientists.

You can also check out these cool telescopes that will help you see the beauty of planet Saturn.

The Cassini spacecraft was able to take another look at one of Saturn’s strangest features – a bizarre six-sided cloud structure circling the entire north pole. This structure was hinted at when the Voyager spacecraft first visited the planet nearly 30 years ago, and Cassini was able to take a brief look a few years ago with Cassini’s infrared camera. But these latest images provide evidence the hexagon-shaped jet stream is still there, (the north pole has been shrouded in darkness but has now recently emerged into sunlight) and gives scientists the most detail yet to study the intriguing hexagon shape crowning the planet.

The hexagon shape is the path of a jet stream flowing around the north pole, and new images reveal concentric circles, curlicues, walls and streamers not seen in previous images. Much to the delight and bafflement of Cassini scientists, the location and shape of the hexagon in the latest images match up with what they saw in the Voyager pictures.

“The longevity of the hexagon makes this something special, given that weather on Earth lasts on the order of weeks,” said Kunio Sayanagi, from the Cassini imaging team. “It’s a mystery on par with the strange weather conditions that give rise to the long-lived Great Red Spot of Jupiter.”

The hexagon was originally discovered in images taken by the Voyager spacecraft in the early 1980s. It encircles Saturn at about 77 degrees north latitude and has been estimated to have a diameter wider than two Earths. The jet stream is believed to whip along the hexagon at around 100 meters per second (220 miles per hour).

But what causes the hexagon? Scientists aren’t quite sure. Particularly intriguing is where it gets and expels its energy and how it has stayed so organized for so long. The Cassini team plans to search the new images for clues, taking an especially close look at the newly identified waves that radiate from the corners of the hexagon — where the jet takes its hardest turns — and the multi-walled structure that extends to the top of Saturn’s cloud layer in each of the hexagon’s six sides. There’s also the a large dark spot that appeared in a different position in a previous infrared image from Cassini. In the latest images, the spot appears in the 2 o’clock position.

Early hexagon images from Voyager and ground-based telescopes suffered from poor viewing perspectives. Cassini, which has been orbiting Saturn since 2004, has a better angle for viewing the north pole. But the long darkness of Saturnian winter hid the hexagon from Cassini’s visible-light cameras for years. Infrared instruments, however, were able to obtain images by using heat patterns. Those images showed the hexagon is nearly stationary and extends deep into the atmosphere. They also discovered a hotspot and cyclone in the same region.

The visible-light cameras of Cassini’s imaging science subsystem, which have higher resolution than the infrared instruments and the Voyager cameras, got their long-awaited glimpse of the hexagon in January, as the planet approached equinox. Imaging team scientists calibrated and stitched together 55 images to create a mosaic and three-frame movie. The mosaics do not show the region directly around the north pole because it had not yet fully emerged from winter night at that time.

Because Saturn does not have land masses or oceans on its surface to complicate weather the way Earth does, its conditions should give scientists a more elementary model to study the physics of circulation patterns and atmosphere, said Kevin Baines, an atmospheric scientist at NASA’s Jet Propulsion Laboratory, Pasadena, Calif., who has studied the hexagon with Cassini’s visual and infrared mapping spectrometer.

“Now that we can see undulations and circular features instead of blobs in the hexagon, we can start trying to solve some of the unanswered questions about one of the most bizarre things we’ve ever seen in the solar system,” Baines said. “Solving these unanswered questions about the hexagon will help us answer basic questions about weather that we’re still asking about our own planet.”

Source: JPL

November 30, 2009December 24, 2015 by Nicholos Wethington

Lake Asymmetry on Titan Explained

This mosaic of Cassini, SAR, ISS, and VIS images data shows that there are many more lakes in the northern regions of Titan than in the south. The eccentric orbit of Saturn is thought to have caused this imbalance. Image Credit: NASA/JPL/Caltech/University of Arizona/Cassini Imaging Team

If you’ve wanted to take a swim in a lake on Titan, don’t: they’re not lakes like we have here on Earth, composed of methane and ethane instead of water. If you have somehow evolved lungs to breathe and swim in these chemicals, you should take your beach vacation in the northern hemisphere of Titan, where you’ll find many more lakes. Data taken by the Cassini mission has shown that there are more of these methane lakes concentrated in the northern hemisphere of Saturn’s moon than in the southern hemisphere. A recent analysis of the Cassini findings by a team at Caltech has shown that the cause of this asymmetry of lakes is due to the orbit of Saturn.

Because of the eccentricity of Saturn’s orbit around the Sun, there is a constant transfer of methane in Titan’s atmosphere from the south to the north. This effect is called astronomical climate forcing, or the Milankovitch cycle, and is thought to be the cause of ice ages here on Earth. We wrote about the Milankovitch cycles and their influence on climate change just earlier today.

Scientists originally thought that the northern hemisphere was somehow differently structured than the south. Imaging data from Cassini showed that ethane and methane lakes cover 20 times more area in the northern hemisphere than lakes in the south. There also are more half-filled and dried-up lake beds in the north. For example, if the composition of the surface of Titan somehow allowed for more methane and ethane to permeate the ground more in the north, this could have explained the difference. But further data from Cassini has confirmed that there is no great difference in topography between the two hemispheres of Titan.

The seasonal differences on Titan only partially explain the asymmetry of lake formation. One year on Titan is 29.5 Earth years, so about every 15 years the seasons of Titan reverse. In other words, the winter and summer seasons could have caused the evaporation and transfer of gas to the north, where it is cooled and is currently in the form of lakes until the seasons change again.

A team led by Oded Aharonson, associate professor of planetary science at Caltech found that there was much more to the story, though. The seasonal effect could only account for changes in lake depth for each hemisphere to vary by about one meter. Titan’s lakes are hundreds of meters deep on average, and this process is too slow to explain the depth changes we see today. It became apparent that the seasonal differences were only partly contributing to this difference.

“On Titan, there are long-term climate cycles in the global movement of methane that make lakes and carve lake basins. In both cases we find a record of the process embedded in the geology,” Aharonson said in a press release.

The Milankovitch cycle on Titan is likely the cause of the lake imbalance. Summers in the north are long and relatively mild, while those in the south are shorter, but warmer. Over thousands of years, this leads to a net movement of gas towards the north, which then condenses and stays there in liquid form. During southern summer Titan is close to the sun, and during northern summer it is approximately 12% further from the Sun.

Their results appear in the advance online version of Nature Geoscience for November 29th. Animations detailing the transfer are available on Oded Aharonson’s home page.

If Cassini would have been sent to Titan 32,000 years ago, the picture would have been reversed: the south pole would have many more lakes than the north. Conversely, any Titanian deep-lake divers in a few thousand years will fare much better in the lakes of the south.

Source: Eurekalert, Oded Aharonson’s Home Page

November 21, 2009December 24, 2015 by Nancy Atkinson

De Plume! De Plume! Enceladus Raw Flyby Images

Raw images are already being returned from Cassini’s Nov. 21 “E-8” or eighth flyby of the tiger-striped moon Enceladus. Visible in this raw image are several plumes from fissures in the south polar region of the moon. These fissures spew jets of water vapor and other particles hundreds of kilometers from the surface. This flyby included a very different geometry to the flyby trajectory – and a different look at the plumes — approaching within 1,606 kilometers (997.9 miles) of the surface, buzzing over 82 degrees south latitude. This is the last look we’ll have for several years at this intriguing area of Enceladus before winter darkness blankets the area. See below for looks at Baghdad Sulcus, the “tiger stripe” that scientists were focusing on.

While Cassini was taking these high-resolution images of the southern part of the Saturn-facing hemisphere, the Composite Infrared Spectrograph (CIRS) instrument was collecting data to create a contiguous thermal map of Baghdad Sulcus. This image was taken approximately 1,858 kilometers away.

Here’s a look at Baghdad Sulcus from 3,556 kilometers away. And below is a 3-D version, created by Stu Atkinson. Stay tuned for more details on the data gathered from the flyby!

Enceladus canyon 3-D. Credit: NASA/JPL, 3-D by Stu Atkinson

Source: Cassini raw images

Thanks to Stu for alerting us the images were here!

* The title is in reference to the “Fantasy Island” television show.

November 20, 2009December 24, 2015 by Nicholos Wethington

Cassini/IBEX Data Changes View of Heliosphere Shape

Though the Cassini mission has focused intently on scientific exploration of Saturn and its moons, data taken by the spacecraft has significantly changed the way astronomers think about the shape of our Solar System. As the Sun and planets travel through space, the bubble in which they reside has been thought to resemble a comet, with a long tail and blunt nose. Recent data from Cassini combined with that of other instruments, shows that the local intertstellar magnetic field shapes the heliosphere differently.

The Solar System resides in a bubble in the interstellar medium – called the “heliosphere” – which is created by the solar wind. The shape carved out of the interstellar dust by the solar wind has been thought for the past 50 years to resemble a comet, with a long tail and blunted nose shape, caused by the motion of the Solar System through the dust.

Data taken by Cassini’s Magnetospheric Imaging Instrument (MIMI) and the Interstellar Boundary Explorer (IBEX) shows that there is more to the forces that cause the shape than previously thought, and that the shape of the heliosphere more closely resembles a bubble.

The shape of the heliosphere was previously thought to have been carved out solely by the interaction of the solar wind particles with the interstellar medium, the resulting “drag” creating a wispy tail. The new data suggests, however, that the interstellar magnetic field slips around the heliosphere and the outer shell, called the heliosheath, leaving the spherical shape of the heliosphere intact. Below is an image representing what the heliosphere was thought to look like before the new data.

The new data also provide a much clearer indication of how thick the heliosheath is, between 40 and 50 astronomical units. This means that NASA’s Voyager spacecraft, Voyager 1 and Voyager 2, which are both traveling through the heliosheath now, will cross into interstellar space before the year 2020. Previous estimates had put that date as far back as 2030.

MIMI was originally designed to take measurements of Saturn’s magnetosphere and surrounding energetic charged particle environment. Since Cassini is far away from the Sun, though, it also places the spacecraft in a unique position to measure the energetic neutral atoms coming from the boundaries of the heliosphere. Energetic neutral atoms form when cold, neutral gas comes into contact with electrically-charged particles in a plasma cloud. The positively-charged ions in plasma can’t reclaim their own electrons, so they steal those of the cold gas atoms. The resulting particles are then neutrally charged, and able to escape the pull of magnetic fields and travel into space.

Energetic neutral atoms form in the magnetic fields around planets, but are also emitted by the interaction between the solar wind and the interstellar medium. Tom Krimigis, principal investigator of the Magnetospheric Imaging Instrument (MIMI) at Johns Hopkins University’s Applied Physics Laboratory in Laurel, Md and his team weren’t sure if the instruments on Cassini would originally be able to detect sources of energetic neutral atoms from as far out as the heliosphere, but after their four-year study of Saturn, they looked into the data from the instrument to see if any particles had strayed in from sources outside the gas planet. To their surprise, there was enough data to complete a map of the intensity of the atoms, and discovered a belt of hot, high pressure particles where the interstellar wind flows by our heliosheath bubble.

The data from Cassini complements that taken by IBEX and the two Voyager spacecraft. The combined information from IBEX, Cassini and the Voyager missions enabled scientists to complete the picture of our little corner of space. To see a short animation of the heliosphere as mapped by Cassini, go here. The results of the combined imaging were published in Science on November 13th, 2009.

Source: JPL

November 20, 2009December 24, 2015 by Nancy Atkinson

More Cassini Eye Candy: Infrared Saturn, Peek-a-boo Moons

The “wow” factor from the Cassini mission never quits. Here’s the latest image, released just today of Saturn, viewed in near-infrared. This image was taken with Cassini’s wide-angle camera on Oct. 23, 2009 using a spectral filter sensitive to wavelengths of near-infrared light, centered at 890 nanometers. The view was acquired at a distance of approximately 2.6 million kilometers (1.6 million miles) from Saturn. The large shadow south of the equator is from the moon Tethys (1062 kilometers, 660 miles across). The small shadow near the limb of the planet, north of the equator, is the shadow of the moon Mimas (396 kilometers, 246 miles across). Absolutely stunning.

See below for more Cassini goodness of moons playing peek-a-boo with the rings and each other.

Moons hiding behind Saturn's rings. Credit: NASA/JPL/Space Science Institute

Here, Janus and another moon hide behind Saturn’s rings.

You don’t see this every day: a crescent Enceladus being eclipsed by a crescent Rhea. Gorgeous!

Click on the images to go directly to the Cassini image pages. See more gorgeous shots at CICLOPS

November 11, 2009December 24, 2015 by Nancy Atkinson

Stunning Cassini Image to Knock Your Socks Off

What a way to start the day! This image is one of the first things I saw online this morning. The moon Rhea hangs like a pendant against Saturn and its rings. Amazingly, this is a raw image straight from Cassini; it has not been calibrated or enhanced in any way. This is art in its purest form and evidence of the phenomenal and enchanting beauty of the Saturn system, as well as confirmation of what an amazing spacecraft Cassini is.

This image was taken on November 08, 2009 and received on Earth November 09, 2009. The camera was pointing toward Rhea at approximately 1,874,061 kilometers away.

Here’s the link to a higher resolution version.

Source page.

Hat tip to @mars_stu on Twitter

November 2, 2009December 24, 2015 by Nancy Atkinson

Fabulous! Enceladus Raw Flyby Images

Carolyn Porco, the lead for Cassini’s imaging team, warned on Twitter that the flyby of Saturn’s moon Enceladus performed by the spacecraft on Nov. 2 wasn’t really an “imaging” flyby, and that we might have to wait until the Nov. 21 flyby for really good images. But just take a look the images returned so far, with stunning looks at the jets shooting from the moon! Another image takes a close look at the surface. These are raw, unprocessed images, but what images they are! This is the second image from today’s flyby returned by the spacecraft. See below for more.

Image #3 from the Nov. 2 flyby of Enceladus. Credit: NASA/JPL/Space Science Institute

Cassini came within about 100 kilometers (62 miles) of the surface. The spacecraft has gone closer during a previous flyby (25 kilometers or 15 miles). This is the third image sent back so far from this flyby, showing the surface of the tiger-striped, geyser-spewing moon. According to the CICLOPS website, this image was taken in visible green light with the Cassini spacecraft narrow-angle camera at a distance of approximately 14,000 kilometers (8,700 miles) from Enceladus. The plan was for the spacecraft to go deep into the heart of the plume from the geysers on the tiger-striped moon; as of yet no images from the plume have been released. The objective of this flyby was to analyze the particles in the plume with instruments that can detect the size, mass, charge, speed and composition. The spacecraft spent only about a minute in the plume.

A far away view of the plumes from Enceladus. Credit: NASA/JPL/Space Science Institute

Here’s a view from farther away, with the plumes visible against the backlit moon.

We’ll add any more images that become available.

Source: CICLOPS

September 24, 2009December 24, 2015 by Nancy Atkinson

The Saturn System: A Feast for the Eyes

Crescent Rhea and Saturn's rings. Credit: NASA/JPL/Space Science Institute

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The Cassini team released some incredible images earlier this week of the Saturn system during equinox, and followed up with this beauty of a crescent moon Rhea beneath the rings of Saturn. NASA has also put together a multimedia presentation of recent pictures of Saturn, set to music, and it is stunning. Run, don’t walk and click here to watch. (Flash required)

With these great images, it is no wonder that the leader of the Cassini imaging team, Carolyn Porco has been presented with an award for her work, the Lennart Nilsson Award for photography for capturing “worlds that are otherwise hidden from human sight.” The award committee’s citation reads:

“Carolyn Porco combines the finest techniques of planetary exploration and scientific research with aesthetic finesse and educational talent. While her images, which depict the heavenly bodies of the Saturn system with unique precision, serve as tools for the world’s leading experts, they also reveal the beauty of the universe in a manner that is an inspiration to one and all.”

Congratulations Dr. Porco!

Here’s some info about the image above:

Rhea (1528 kilometers, 949 miles across) is near the middle of the bottom of the image. This view looks toward the northern, sunlit side of the rings from about 4 degrees above the ringplane.

The image was taken in visible light with the Cassini spacecraft wide-angle camera on Aug. 24, 2009. The view was obtained at a distance of approximately 1.6 million kilometers (994,000 miles) from Saturn and at a Sun-Saturn-spacecraft, or phase, angle of 137 degrees. Image scale is 95 kilometers (59 miles) per pixel.

For more images see the CICLOPS (Cassini Imaging Central Laboratory for Operations) website.

September 21, 2009December 24, 2015 by Nancy Atkinson

New Equinox Stunners From Cassini

Saturn at Equinox. credit: NASA/JPL/Space Science Institute

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Every 14.8 Earth years, equinox occurs at Saturn. But this is the first time there has been a spacecraft in situ to watch what happens when the sun is directly overhead at the equator, illuminating the rings directly edge-on. New images compiled from the Cassini spacecraft show a rare and breathtaking display of nature: the setting of the sun on Saturn’s rings. The image above — a mosaic of 75 different images — shows the beauty of this ringed world, but the most surprising revelation from these new images are that newly discovered lumps and bumps in the rings are as high as the Rocky Mountains.

Saturn's rings reaching new heights. Credit: NASA/Space Science Institute

The shadows in this image have lengths as long as 500 kilometers (310 miles), meaning the structures casting the shadows reach heights of almost 4 kilometers (2.5 miles) above the ringplane. These heights are much greater than those previously observed for the Daphnis edge waves, and are very likely caused by the distance between Daphnis and the inner edge of its gap getting unusually small at certain times

“We thought the plane of the rings was no taller than two stories of a modern-day building and instead we’ve come across walls more than 2 miles [3 kilometers] high,” said Carolyn Porco, Cassini imaging team leader at the Space Science Institute in Boulder, Colo. “Isn’t that the most outrageous thing you could imagine? It truly is like something out of science fiction.”

“The biggest surprise was to see so many places of vertical relief above and below the otherwise paper-thin rings,” said Linda Spilker, deputy project scientist at JPL. “To understand what we are seeing will take more time, but the images and data will help develop a more complete understanding of how old the rings might be and how they are evolving.”

Propeller feature in the rings. Credit: NASA/Space Science Institute

An unusually large propeller feature has been detected just beyond the Encke Gap in this Cassini image of Saturn’s outer A ring, taken a couple days after the planet’s August 2009 equinox. Propeller-like features, a few kilometers long, centered on and created by the action of small embedded moonlets only about 330 feet (100 meters) across, were discovered early in the mission. These findings constituted the first recognition that bodies smaller than the 8-kilometer-wide ring moon, Daphnis, in the outer A ring and bigger than the largest ring particles (about 30 feet, or 10 meters, across) were present in Saturn’s rings.

New insights into the nature of Saturn's rings are revealed in this panoramic mosaic of 15 images taken during the planet's August 2009 equinox.

Waves in the inner B ring, first seen in Saturn orbit insertion images, are now more obvious and distinct. This mosaic combines 15 separate images. Also visible are bright spokes, consisting of tiny particles elevated above the ring plane and surrounded by the dark outer B ring, can also be seen near the middle of the mosaic.

These two Cassini images, taken four years before Saturn’s August 2009 equinox, have taken on a new significance as data gathered at equinox indicate the streaks in these images are likely evidence of impacts into the planet’s rings.

In one unexpected equinox discovery, imaging scientists have uncovered evidence for present-day impacts onto the rings. Bright, and hence elevated, clouds of tiny particles, sheared out by orbital motion into streaks, up to 3,000 miles (5,000 kilometers) long, have been sighted in the A and C rings. These clouds — very likely thrown up by impacts — rising above the dark ring plane are more directly catching the sun’s rays during equinox, and are hence well lit and easily visible by contrast.

By the brightness and dimensions of the streaks, scientists estimate the impactor sizes at roughly one meter, and the time since impact at one to two days. These equinox data now lend more confidence to the impact interpretation of earlier Cassini images, taken in 2005, showing similar streaks in the C ring. In the 2005 images, the impactors are likely much smaller than one meter, and yet have left a visible ejecta cloud. All together, these observations are heralded as the first visual confirmation of a long-held belief that bits of interplanetary debris continually rain down on Saturn’s rings and contribute to their erosion and evolution.

Summing up the past several months of Cassini’s exploration of Saturn during this unusual celestial event, imaging team leader Carolyn Porco in Boulder, Colo., said, “This has been a moving spectacle to behold, and one that has left us with far greater insight into the workings of Saturn’s rings than any of us could have imagined. We always knew it would be good. Instead, it’s been extraordinary.”

For more images and information see CICLOPS.