The Return of the Rings!

Now that Cassini has gone off on a new trajectory taking it above and below the equatorial plane of Saturn, we’re back to getting some fantastic views of the rings — the likes of which haven’t been seen in over two and a half years!

The image above shows portions of the thin, ropy F ring and the outer A ring, which is split by the 202-mile (325-km) -wide Encke gap. The shepherd moon Pan can be seen cruising along in the gap along with several thin ringlets. Near the A ring’s outer edge is a narrower space called the Keeler gap — this is the home of the smaller shepherd moon Daphnis, which isn’t visible here (but is one of my personal favorites!)

The scalloped pattern on the inner edge of the Encke gap downstream from Pan and a spiral pattern moving inwards from that edge are created by the 12.5-mile-wide (20-km-wide) moon’s gravitational influence.

Other features that have returned for an encore performance are the so-called propellers, spiral sprays of icy ring material created by tiny micro-moons within the rings. Individually too small to discern (less than half a mile in diameter) these propeller moons kick up large clumps of reflective ring particles with their gravity as they travel through the rings, revealing their positions.

The three images above show a propeller within the A ring. Nicknamed “Sikorsky” after Russian-American aviator Igor Sikorsky, the entire structure is about 30 miles (50 km) across and is one of the more well-studied propellers.

Scientists are eager to understand the interactions of propellers in Saturn’s rings as they may hold a key to the evolution of similar systems, such as solar systems forming from disks of matter.

See a video of a propeller orbiting within the rings here, and here’s an image of one that’s large enough to cast a shadow!

“One of the main contributing factors to the enormous success we on the Cassini mission have enjoyed in the exploration of Saturn is the capability to view the planet and the bodies around it from a variety of directions,” Cassini Imaging Team Leader Carolyn Porco wrote earlier today. “Setting the spacecraft high into orbit above Saturn’s equator provides us direct views of the equatorial and middle latitudes on the planet and its moons, while guiding it to high inclination above the equator plane affords the opportunity to view the polar regions of these bodies and be treated to vertigo-inducing shots of the planet’s glorious rings.”

As always, keep up with the latest Cassini news on the mission site here, and read more about these images on the CICLOPS imaging team page here.

Image credits: NASA / JPL / Space Science Institute.

 

Cassini Captures a Rarely-Seen Moon

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While many of us here on Earth were waiting for the Moon to take a bite out of the Sun this past Sunday, Cassini was doing some moon watching of its own, 828.5 million miles away!

The image above is a color-composite raw image of Methone (pronounced meh-tho-nee), a tiny, egg-shaped moon only 2 miles (3 km) across. Discovered by Cassini in 2004, Methone’s orbit lies between Mimas and Enceladus, at a distance of 120,546 miles (194,000 km) from Saturn — that’s about half the distance between Earth and the Moon.

At an altitude of 1,200 miles (1900 km) this was Cassini’s closest pass ever of Methone, a rare visit that occurred after the spacecraft departed the much larger Tethys.

Along with sister moons Pallene and Anthe, Methone is part of a group called the Alkyonides, named after daughters of the god Alkyoneus in Greek mythology. The three moons may be leftovers from a larger swarm of bodies that entered into orbit around Saturn — or they may be pieces that broke off from either Mimas or Enceladus.

Earlier on Sunday, May 20, Cassini paid a relatively close visit to Tethys (pronounced tee-this), a 662-mile (1065-km) -wide moon made almost entirely of ice. One of the most extensively cratered worlds in the Solar System, Tethys’ surface is dominated by craters of all sizes — from the tiniest to the giant 250-mile (400-km) -wide Odysseus crater — as well as gouged by the enormous Ithaca Chasma, a series of deep valleys running nearly form pole to pole.

Saturn's icy moon Tethys with Ithaca Chasma visible, seen by Cassini on May 20, 2012.
Tethys' rugged and heavily-cratered surface near the terminator
Cassini looks down into the 62 mile (100 km) wide Ithaca Chasma

Cassini passed within 34,000 miles (54,000 km) of Tethys on May 20, before heading to Methone and then moving on to its new path toward Titan, a trajectory that will eventually take it up out of Saturn’s equatorial plane into a more inclined orbit in order to better image details of the rings and  Saturn’s poles.

Read more about this flyby on the Cassini mission site here. and see more raw images straight from the spacecraft on the CICLOPS imaging lab site here.

Image credit: NASA / JPL / Space Science Institute. (Color-composite image edited by J. Major.)

A New Angle on Titan

Here’s a great shot of Titan and Saturn acquired by Cassini on May 6, 2012 just after a pass by the haze-covered moon. It’s a color-composite made from images taken in Cassini’s red, green and blue color channels, and the resulting image was color adjusted a bit to appear more “Saturny”.

UPDATE 7/2/12: The image above is featured in today’s Astronomy Picture of the Day (APOD)… check it out here.

Cassini also made some closer passes of Titan on May 6, taking images within about 710,000 km. After recent passes of Encealdus and Dione, Cassini buzzed past Titan in preparation of a targeted flyby on May 22, after which it will head up and out out of the “moonplane” in order to get a better view of Saturn’s rings and upper latitudes.

After that, Cassini won’t be playing amongst the moons again for three years, so images like this will be a rarity for a while.

Another image of Titan, closer-in and set against Saturn’s rings and clouds, shows the fine, transparent structure of the moon’s upper atmospheric haze layers:

Created by the breakdown of methane in Titan’s opaque atmosphere by UV radiation, the haze is composed of complex hydrocarbons that extend outwards up to ten times the thickness of Earth’s atmosphere!

(The RGB layers weren’t available for this particular view, so there’s no color version of it.)

Check out previous images from Cassini’s flyby of Dione and Enceladus, and follow along with the Cassini mission on the JPL site here.

Top image: Color-composite image of Titan and Saturn (NASA/JPL/SSI/J. Major) Bottom image: Titan in blue wavelength against Saturn (NASA/JPL/SSI)

ESA Turns On The JUICE For New Jupiter Mission

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The European Space Agency has given the go-ahead for an exciting mission to explore the icy moons of Jupiter, as well as the giant planet itself.

JUICEJUpiter ICy moons Explorer — will consist of a solar-powered spacecraft that will spend 3.5 years within the Jovian system, investigating Ganymede, Europa and the upper atmosphere of Jupiter. Anticipated to launch in June 2022, JUICE would arrive at Jupiter in early 2030.

As its name implies, JUICE’s main targets are Jupiter’s largest icy moons — Ganymede and Europa — which are thought to have liquid oceans concealed beneath their frozen surfaces.

The largest moon in the Solar System, Ganymede is also thought to have a molten iron core generating a magnetic field much like Earth’s. The internal heat from this core may help keep Ganymede’s underground ocean liquid, but the dynamics of how it all works are not quite understood.

JUICE will also study the ice-coated Europa, whose cueball-smooth surface lined with cracks and jumbled mounds of frozen material seem to be sure indicators of a subsurface ocean, although how deep and how extensive is might be are still unknown — not to mention its composition and whether or not it could be hospitable to life.

The rust-colored cracks lining Europa's otherwise smooth surface hint at a subsurface ocean. (Ted Stryk)

“JUICE will give us better insight into how gas giants and their orbiting worlds form, and their potential for hosting life,” said Professor Alvaro Giménez Cañete, ESA’s Director of Science and Robotic Exploration.

The JUICE spacecraft was originally supposed to join a NASA mission dedicated to the investigation of Europa, but NASA deemed their proposed mission too costly and it was cancelled. According to Robert Pappalardo, study scientist for the Europa mission based at JPL, NASA may still supply some instruments for the spacecraft “assuming that the funding situation in the United States can bear it.”

Artist's rendering of JUICE at Jupiter. (ESA/AOES)

JUICE will also capture images of Jupiter’s moon Callisto and search for aurorae in the gas giant’s upper atmosphere, as well as measure the planet’s powerful magnetic field. Once arriving in 2030, it will spend at least three years exploring the Jovian worlds.

Read more in today’s news release from Nature, and stay tuned to ESA’s JUICE mission page here.

Recalibrated Galileo images © Ted Stryk. See more of Ted’s excellent work on his site Planetary Images From Then And Now.

Cassini Slips Through Enceladus’ Spray

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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.)

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.)

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.

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.

 

Postcards From Saturn

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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!

110-mile (177-km) -wide Janus in front of Saturn's night side.
A crescent-lit Enceladus shows off its jets. (South is up.)
Enceladus' fractured surface is some of the most reflective terrain in the Solar System.
Wide-angle view of Rhea, Saturn and Mimas
Crater peak on icy Dione

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:

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.

Two Moons In Passing

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Saturn’s moon Tethys passes in front of its slightly larger sister Dione in this animation made from 25 raw images acquired by Cassini on March 14, 2012. Pretty cool! (Click the image to play.)

 

Tethys and Dione (NASA/JPL/SSI)

Tethys and Dione are similar in diameter, being 1,062 kilometers (660 miles) wide and 1,123 kilometers (698 miles) wide, respectively. Both are heavily cratered, ice-rich worlds.

In this view, Tethys’ enormous Odysseus crater can be seen on its northern hemisphere. 400 km (250 miles) across, Odysseus is two-fifths the diameter of Tethys itself, suggesting that it was created early in the moon’s history when it was still partially molten — or else the impact would have shattered the moon apart entirely.

The more extensively-cratered trailing side of Dione is visible here, its signature “wispy lines” rotated out of view. Since it makes sense that a moon’s leading face should be more heavily cratered, it’s thought that Dione has been spun around by an impact event in the distant past.

If you look closely, a slight rotation in Tethys can also be discerned from the first frame to the last.

Credit: NASA/JPL/SSI. Animation by Jason Major.

Photo Treat: Enceladus, Titan and Saturn’s Rings

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Little Enceladus and enormous Titan are seen on either side of Saturn’s rings in this image, a color-composite made from raw images acquired by Cassini on March 12, 2012. The original images were taken in red, green and blue color channels, and with a little Photoshop editing I combined them into a roughly true-color view of what Cassini saw as it passed within 1,045,591 km of Enceladus.

Follow along with the Cassini mission here.

Image credit: NASA/JPL/Space Science Institute. Edited by Jason Major.

Moons Large and Small

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It may be one of the best images from Cassini yet this year! Cloud-covered Titan and tiny Prometheus (can you see it just above the rings on the right?) are literally dwarfed by their parent Saturn in an image captured on Jan. 5, 2012.

Prometheus’ pinpoint shadow can also be seen on Saturn’s cloud tops, just inside the thin, outermost F ring shadow at bottom left.

The two moons themselves couldn’t be more different; Titan, 3,200 miles (5,150 km) wide, is wrapped in a nitrogen and methane atmosphere ten times thicker than Earth’s and is covered with vast plains of dark hydrocarbon dunes and crisscrossed by rivers of liquid methane.

Prometheus imaged by Cassini in Dec. 2009.

Prometheus, on the other hand, is a potato-shaped shepherd moon 92 miles long and 53 miles wide (148 x 53 km) that orbits Saturn just inside the narrow, ropy F ring. While it doesn’t have an atmosphere, it does create some impressive effects on the icy material in the ring!

Another moon, Pandora, casts its shadow onto Saturn just outside the F ring shadow at bottom center. 50 miles (80 km) wide, Pandora shepherds the outer edge of the F ring but is itself not visible in this image. Watch an animation here.

This image was featured on the Cassini Imaging Central Laboratory for Operations (CICLOPS) website on Feb. 28, 2012. The view looks toward the southern, unilluminated side of the rings from about 1 degree below the ringplane.

Image credit: NASA / JPL / Space Science Institute.

Does Earth Have Many Tiny Moons?

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Look up in a clear night sky. How many moons do you see? Chances are, you’re only going to count to one. Admittedly, if you count any higher and you’re not alone, you may get some funny looks cast in your direction. But even though you may not be able to actually see them, there may very well be more moons out there orbiting our planet.

For the time being, anyway.

Today, Earth has one major moon in orbit around it. (Technically the Earth-Moon system orbits around a common center of gravity, called the barycenter, but that’s splitting hairs for the purpose of this story.) At one time Earth may have had two large moons until the smaller eventually collided into the larger, creating the rugged lump we now call the farside highlands. But, that was 4 billion years ago and again not what’s being referred to here.

Right now, at his moment, Earth may very well have more than the one moon we see in the night sky. Surprise.

Of course, it would be a very small moon. Perhaps no more than a meter across. But a moon nonetheless. And there could even be others – many others – much smaller than that. Little bits of solar system leftovers, orbiting our planet even farther out than the Moon we all know and love, coming and going in short-lived flings with Earth without anyone even knowing.

This is what has been suggested by researcher Mikael Granvik of the University of Helsinki in Finland. He and his colleagues have created computer simulations of asteroids believed to be occupying the inner solar system, and what the chances are that any number of them could be captured into Earth orbit at any given time.

Orbit of 2006 RH120, a confirmed TCO identified in 2006.

The team’s results, posted Dec. 20 in the science journal Icarus, claim it’s very likely that small asteroids would be temporarily captured into orbit (becoming TCOs, or temporarily captured objects) on a regular basis, each spending about nine months in up to three revolutions around Earth before heading off again.

Some objects, though, might hang around even longer… in the team’s simulations one TCO remained in orbit for 900 years.

“There are lots of asteroids in the solar system, so chances for the Earth to capture one at any time is, in a sense, not surprising,” said co-author Jeremie Vauballion, an astronomer at the Paris Observatory.

In fact, the team suspects that there’s most likely a TCO out there right now, perhaps a meter or so wide, orbiting between 5 and 10 times the distance between Earth and the Moon. And there could be a thousand smaller ones as well, up to 10 centimeters wide.

So if these moons are indeed out there, why don’t we know about them?

Put simply, they are too small, too far, and too dark.

At that distance an object the size of a writing desk is virtually undetectable with the instruments we have now.. especially if we don’t even know exactly where to look. But in the future the Large Synoptic Survey Telescope (LSST) may, once completed, be able to spot these tiny satellites with its 3200-megapixel camera.

Once spotted, TCOs could become targets of exploration. After all, they are asteroids that have come to us, which would make investigation all the easier – not to mention cheaper – much more so than traveling to and back from the main asteroid belt.

“The price of the mission would actually be pretty small,” Granvik said. And that, of course, makes the chances of such a mission getting approved all the better.

Read more on David Shiga’s article on New Scientist here.

The team’s published paper can be found here.