Help Name Pluto’s Newest Moons!

Pluto's known system of moons (NASA/ESA/M. Showalter))

Today marks seven months since the announcement of Pluto’s fifth moon and over a year and a half since the discovery of the one before that. But both moons still have letter-and-number designations, P5 and P4, respectively… not very imaginative, to say the least, and not really fitting into the pantheon of mythologically-named worlds in our Solar System.

Today, you can help change that.

According to the New Horizons research team, after the discovery of P4 in June 2011 it was decided to wait to see if any more moons were discovered in order to choose names that fit together as a pair, while a*lso following accepted IAU naming practices. Now, seven months after the announcement of P5, we think a decision is in order… and so does the P4/P5 Discovery Team at the SETI Institute.

"Hey, I can be democratic about this!"
“Hey, I can be democratic about all this!”

Today, SETI Senior Research Scientist Mark Showalter revealed a new poll site, Pluto Rocks, where visitors can place their votes on a selection of names for P4 and P5 — or even write in a suggestion of their own. In line with IAU convention these names are associated with the Greek and Roman mythology surrounding Pluto/Hades and his underworld-dwelling minions.

“In 1930, a little girl named Venetia Burney suggested that Clyde Tombaugh name his newly discovered planet ‘Pluto.’ Tombaugh liked the idea and the name stuck. I like to think that we are doing honor to Tombaugh’s legacy by now opening up the naming of Pluto’s two tiniest known moons to everyone.”

– Mark Showalter, SETI Institute

As of the time of this writing, the ongoing results look like this:

Results of Pluto Rocks voting as of Feb. 11, 2013 at 10 am EST (15:00 UT)
Results of Pluto Rocks voting as of Feb. 11, 2013 at 10 am EST (15:00 UT)

Do you like where the voting is headed? Are you hellishly opposed? Go place your vote now and make your opinion count in the naming of these two distant worlds!

(After all, New Horizons will be visiting Pluto in just under two and a half years, and she really should know how to greet the family.)

Voting ends at noon EST on Monday, February 25th, 2013.

The SETI team welcomes you to submit your vote every day, but only once per day so that voting is fair.

UPDATE: On Feb. 25, the final day of voting, the tally is looking like this:

PlutoRocks results as of Feb. 25, 2013 - Vulcan is in the lead, thanks to publicity from Mr. William Shatner
PlutoRocks results as of Feb. 25, 2013 – Vulcan is in the lead, thanks to publicity from Mr. William Shatner

Thanks in no small part to a bit of publicity on Twitter by Captain Kirk himself, Mr. William Shatner (and support by Leonard Nimoy) “Vulcan” has made the list and warped straight to the lead. Will SETI and the IAU honor such Trek fan support with an official designation? We shall soon find out…

The Rings on the Planet Go ‘Round and ‘Round…

Raw wide-angle Cassini image of Saturn’s rings (NASA/JPL/SSI)

Recently I posted an image of two of Saturn’s shepherd moons, Pandora and Prometheus, captured by Cassini in a face-off across the spindly F ring. Now here’s a much wider-angle view of the gas giant’s rings, seen by Cassini  two days later on December 20, and the same two moons can still be seen staring each other down… two tiny points of light visible across the wavering line of the F ring at lower center.

This is just one raw image in a series of 56 that Cassini captured on the 20th, and I’ve combined them together to make a GIF animation — click below to watch:

Animation of Saturn’s rings made from raw images acquired by Cassini on Dec. 20, 2012 (NASA/JPL/SSI. Animation by J. Major)

In the animation you can see Pandora and Prometheus promenade around Saturn (detail at right) as well as a “spoke” of light material moving within the inner dark edge of the A ring. Also many clumps are visible in the thin F ring — caused by embedded moonlets and the gravitational influence of the shepherd moons.

Saturn’s enormous shadow engulfs the entire ring system at the top of the scene.

Cassini was moving relative to Saturn while these images were captured so some background stars make brief appearances, as well as a couple of pixel flares and a cosmic ray hit. These are common in Cassini images.

See more news and images from the Cassini mission here.

 

Shepherd Moon Face-Off!

Raw Cassini image acquired on Dec. 18, 2012 (NASA/JPL/SSI)

Two of Saturn’s shepherd moons face off across the icy strand of the F ring in this image, acquired by the Cassini spacecraft on December 18, 2012.

In the left corner is Pandora, external shepherd of the ropy ring, and in the right is Prometheus, whose gravity is responsible for the subtle tug on the wispy ring material. (Please don’t blame the moon for any recent unsatisfying sci-fi films of the same name. There’s no relation, we promise.)

Similar in size (Pandora is 110 x 88 x 62 km, Prometheus 148 x 100 x 68 km) both moons are porous, icy, potato-shaped bodies covered in craters — although Prometheus’ surface is somewhat smoother in appearance than Pandora’s, perhaps due to the gradual buildup of infalling material from the F ring.

Check out some much closer images of these two moons below, acquired during earlier flybys:

Here’s Pandora, as seen by Cassini on September 5, 2005:

False-color image of Pandora (NASA/JPL/SSI)

…and here’s Prometheus, seen during a close pass in 2010 and color-calibrated by Gordan Ugarkovic:

 Prometheus casting a shadow through F ring haze (NASA/JPL/SSI/Gordan Ugarvovic)

The external edge of the A ring with the thin Keeler gap and the wider Encke gap can be seen at the right of the top image. Both of these gaps also harbor their own shepherd moons — Daphnis and Pan, respectively.

These moons keep their gaps clear, as well as maintain the crisp edge shapes of the nearby rings — hence the term “shepherd.”

Image credit: NASA/JPL/Space Science Institute

Titan’s Gravity Indicates a Thicker, Uneven Icy Crust

Color composite of Titan and Dione made from Cassini images acquired in May 2011. (NASA/JPL/SSI/J. Major)

It’s long been speculated that Saturn’s moon Titan may be harboring a global subsurface ocean below an icy crust, based on measurements of its rotation and orbit by NASA’s Cassini spacecraft. Titan exhibits a density and shape that indicates a pliable liquid internal layer — an underground ocean — possibly composed of water mixed with ammonia, a combination that would help explain the consistent amount of methane found in its thick atmosphere.

Now, further analysis of Cassini gravity measurements by a Stanford University team has shown that Titan’s ice layer is thicker and less uniform than originally estimated, indicating a more complex internal structure — and a stronger external influences for its heat.

Titan’s liquid subsurface ocean was previously estimated to be in the neighborhood of 100 km (62 miles) thick, sandwiched between a rocky core below and an icy shell above. This was based on the behavior of Titan in its orbit — or, more precisely, how Titan’s shape changes along the course of its orbit, as measured by Cassini’s radar instrument.

Because Titan’s 16-day orbit is not perfectly circular the moon experiences a stronger gravitational pull from Saturn at certain points than at others. As a result it’s flattened at the poles and constantly changing shape slightly — an effect called tidal flexing. Along with the decay of radioactive materials in its core, this flexing generates the internal heat that helps keep a subsurface ocean liquid.

A team of researchers from Stanford University, led by Howard Zebker, professor of geophysics and electrical engineering, used recent Cassini measurements of Titan’s topography and gravity to determine that the icy layer between the moon’s surface and ocean is up to twice as thick as previously thought — and it’s considerably thicker at the equator than at the poles.

“The picture of Titan that we get has an icy, rocky core with a radius of a little over 2,000 kilometers, an ocean somewhere in the range of 225 to 300 kilometers thick and an ice layer that is 200 kilometers thick,” said Zebker.

Different thicknesses of Titan’s ice layer would mean that there’s less heat being generated internally by the decay of radioactive materials in Titan’s core, because that type of heat would be more or less globally uniform. Instead, tidal flexing caused by the gravitational interactions with Saturn and neighboring smaller moons must play a stronger role in heating Titan’s insides.

Read more: Titan’s Tides Suggest a Subsurface Sea

With Cassini’s new measurements of Titan’s gravity, Zebker and his team calculated that the icy layer below Titan’s flattened poles is 3,000 meters (about 1.8 miles) thinner than average, while at the equator it’s 3,000 meters thicker than average. Combined with the moon’s surface features, this makes the average global thickness of the ice layer to be more like 200 km, not 100.

Heat generated by tidal flexing — which is more strongly felt at the poles — is thought to be the cause of the thinner ice there. Thinner ice would mean there’s more liquid water beneath the poles, which is denser and thus would exert a stronger gravitational pull… exactly what’s been found in Cassini’s measurements.

The findings were announced Tuesday, Dec. 4 at the AGU convention in San Francisco. Read more on the Stanford University news page.

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

Closest view of Saturn's moon Methone ever captured by Cassini

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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

Color-composite image of Titan and Saturn (NASA/JPL/SSI/J. Major)

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

Galileo image of Ganymede, Jupiter's - and the Solar System's - largest moon. (Ted Stryk)

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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

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.)

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

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!

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.