Posted on by Jason Major

Bolt from the Blue: Giant Flash of Lightning Seen in Saturn’s Storm

An enormous storm that wrapped its way around Saturn’s northern hemisphere during the first half of 2011 wasn’t just a churning belt of high-speed winds; it also generated some monster flashes of lightning as well — one of which was captured on camera by the Cassini spacecraft!

Check it out…


The image above was created from Cassini raw images acquired in red, green, and blue color channels and assembled to create a somewhat “true-color” image of Saturn. The image shows the storm as it looked on February 25, 2011, a couple of months after it was first noticed by amateur astronomers on the ground. (The circle at upper left illustrates the comparative size of Earth.)

Read: Studying Saturn’s Super Storm

These images were acquired by Cassini almost two weeks later, on March 6, the first showing a bright blue flash of lightning within the storm, along the eastern edge of a large eddy. The second image, taken 30 minutes later, does not have any visible flash.

Because the flash was only visible in blue light (and there was no red channel data) the images are false color. Near-infrared replaced the visible red channel.

Based on the image resolution (12 miles/20 km per pixel) the size of the lightning flash is estimated to be about 120 miles (200 km) wide — as large as the strongest lightning seen on Earth. And like on Earth, Saturn’s lightning is thought to originate deeper in the atmosphere, at the level where water droplets freeze.

Although the 2011 northern storm was a great feature to observe, this wasn’t the first time lightning had been spotted on Saturn. Cassini had observed flashes on the ringed planet in August of 2009 as well, allowing scientists to create the first movie of lightning flashing on another planet.

Since its arrival at Saturn in 2004, Cassini has detected 10 lightning storms on Saturn — although with up to 10 flashes per second and eventually covering an area of 2 billion square miles (4 billion sq. km) the 2011 storm was by far the largest ever seen.

Image credits: NASA / JPL-Caltech / Space Science Institute. Top composite by J. Major. Video: JPL

Posted on by Jason Major

Surprising Swirls Above Titan’s South Pole

View of Titan's South Pole, showing a vortex. Credit: NASA

Thanks to Cassini’s new vantage point granted by its inclined orbit researchers have gotten a new look at the south pole of Titan, Saturn’s largest moon. What they’ve recently discovered is a swirling vortex of gas forming over the moon’s pole, likely the result of the approach of winter on Titan’s southern hemisphere.

What we’re seeing here is thought to be an open cell convection process in Titan’s upper atmosphere. In open cells, air sinks in the center of the cell and rises at the edge, forming clouds at cell edges. However, because the scientists can’t see the layer underneath the layer visible in these new images, they don’t know what other mechanisms may be at work.

A stable atmospheric event that’s found here on Earth as well, open cell convection can be compared to the action of boiling water.

Titan has already been seen to have a thicker area of high-altitude haze over its north pole, and as autumn progresses toward winter in Titan’s south during the course of Saturn’s 29.7-year-long orbit this may very well be the beginnings of a southern polar hood.

An animation of this southern vortex can be found here.

“We suspect that this maelstrom, clearly forming now over the south pole and spinning more than forty times faster than the moon’s solid body, may be a harbinger of what will ultimately become a south polar hood as autumn there turns to winter.  Of course, only time will tell.”

– Carolyn Porco, Cassini Imaging Team Leader

Discoveries like this are prime examples of why it was so important for Cassini to have an extended, long-duration mission around Saturn, so that seasonal changes in the planet and moons could be closely observed. New seasons bring new surprises!

The southern vortex structure was also captured in raw images acquired by Cassini on June 28. A color-composite made from three of those raw images is below (the vortex can be seen at center just right of the terminator):

You can find more images from Cassini on the CICLOPS Imaging Team site.

Image credits: NASA/JPL/Space Science Institute. Bottom RGB composite by Jason Major.

Posted on by Jason Major

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.

 

Posted on by Jason Major

An Epic Crater Called Odysseus

On June 28 NASA’s Cassini spacecraft passed by Tethys, a 1,062-kilometer (662-mile) -wide moon of Saturn that’s made almost entirely of ice. Tethys is covered in craters of all sizes but by far the most dramatic of all is the enormous Odysseus crater, which spans an impressive 450 kilometers (280 miles) of the moon’s northern hemisphere — nearly two-fifths of its entire diameter!

In fact, whatever struck Tethys in the distant past probably should have shattered it into pieces… but didn’t.

Tethys likely held itself together because when the impact occurred that formed Odysseus, the moon was still partially molten. It was able to absorb some of the energy of the impact and thus avoid disintegration — although it was left with a quite the battle scar as an eternal reminder.

The images below are raw images from Cassini’s latest pass of Tethys, showing the moon’s rugged terrain and portions of Odysseus from a distance of 68,521 kilometers (42,577 miles).

The central peak of Odysseus has collapsed, leaving a depression — another indication that the moon wasn’t entirely solid at the time of impact.

Tethys orbits Saturn at a distance of 294,660 kilometers (183,100 miles), about 62,000 miles closer than the Moon is from Earth. Such a close proximity to Saturn subjects Tethys to tidal forces, the frictional heating of which likely helped keep it from cooling and solidifying longer than more distant moons. As a result Tethys appears somewhat less cratered than sister moons Rhea and Dione, which still bear the marks of their earliest impacts… although looking at the region south of Odysseus it’s hard to image a more extensively-cratered place.

Tethys is just another reminder of the violent place our solar system can be. Find out more about Tethys on the Cassini mission site here.

Image credits: NASA/JPL/Space Science Institute. Edited by J. Major. Images have not been calibrated or validated, and each has been level-adjusted and sharpened to bring out surface detail, and in some areas deinterlacing was used to remove linear raw image artifacts.

Posted on by Jason Major

Titan’s Tides Suggest a Subsurface Sea

Saturn’s hazy Titan is now on the short list of moons that likely harbor a subsurface ocean of water, based on new findings from NASA’s Cassini spacecraft.

As Titan travels around Saturn during its 16-day elliptical orbits, it gets rhythmically squeezed by the gravitational pull of the giant planet — an effect known as tidal flexing (see video below.) If the moon were mostly composed of rock, the flexing would be in the neighborhood of around 3 feet (1 meter.) But based on measurements taken by the Cassini spacecraft, which has been orbiting Saturn since 2004, Titan exhibits much more intense flexing — ten times more, in fact, as much as 30 feet (10 meters) — indicating that it’s not entirely solid at all.

Instead, Cassini scientists estimate that there’s a moon-wide ocean of liquid water beneath the frozen crust of Titan, possibly sandwiched between layers of ice or rock.

“Short of being able to drill on Titan’s surface, the gravity measurements provide the best data we have of Titan’s internal structure.”

– Sami Asmar, Cassini team member at JPL

“Cassini’s detection of large tides on Titan leads to the almost inescapable conclusion that there is a hidden ocean at depth,” said Luciano Iess, the paper’s lead author and a Cassini team member at the Sapienza University of Rome, Italy. “The search for water is an important goal in solar system exploration, and now we’ve spotted another place where it is abundant.”

Although liquid water is a necessity for the development of life, the presence of it alone does not guarantee that alien organisms are swimming around in a Titanic underground ocean. It’s thought that water must be in contact with rock in order to create the necessary building blocks of life, and as yet it’s not known what situations may exist around Titan’s inner sea. But the presence of such an ocean — possibly containing trace amounts of ammonia — would help explain how methane gets replenished into the moon’s thick atmosphere.

“The presence of a liquid water layer in Titan is important because we want to understand how methane is stored in Titan’s interior and how it may outgas to the surface,” said Jonathan Lunine, a Cassini team member at Cornell University, Ithaca, N.Y. “This is important because everything that is unique about Titan derives from the presence of abundant methane, yet the methane in the atmosphere is unstable and will be destroyed on geologically short timescales.”

The team’s paper appears in today’s edition of the journal Science. Read more on the Cassini mission site here.

Top image: artist’s concept showing a possible scenario for the internal structure of Titan. (A. Tavani). Side image: An RGB-composite color image of Titan and Dione in front of Saturn’s face and rings, made from Cassini images acquired on May 21, 2011. (NASA/JPL/SSI. Composite by J. Major.)

Posted on by Nancy Atkinson

Extremes in the Saturn System

It’s just one extreme to another in this image from the Cassini spacecraft. Of course, you can’t miss the ginormous Saturn. But do you see three of what appear to be eentsy, tiny moons of the ringed planet?

Tethys (660 miles, or 1,062 kilometers across) is on the right of the image, below the rings. Smaller Enceladus (313 miles, or 504 kilometers across) is on the left of the view, below the rings. Pandora (50 miles, or 81 kilometers across) is also present in this view but is barely visible. It appears as a small grey speck above the rings on the extreme left edge of the image. Pandora has been slightly brightened by the imaging team by a factor 1.2 relative to the rest of the image.

The image was taken with the Cassini spacecraft wide-angle camera on Dec. 7, 2011 using a spectral filter sensitive to wavelengths of near-infrared light centered at 752 nanometers. The view was obtained at a distance of approximately 1.3 million miles (2.1 million kilometers) from Saturn. Image scale is about 77 miles (124 kilometers) per pixel.

Image caption: Saturn and three small moons. Credit: NASA/JPL-Caltech/Space Science Institute

Source: CICLOPS

Posted on by Nancy Atkinson

Cassini Spies a Possible ‘Oasis’ on Titan

Saturn's rings lie in the distance as the Cassini spacecraft looks toward Titan and its dark region called Shangri-La, east of the landing site of the Huygens Probe. Image Credit: NASA/JPL-Caltech/Space Science Institute

From a JPL press release:

New data from the Cassini spacecraft shows enduring methane lakes in the equatorial regions on Saturn’s moon Titan. Previous models of the frigid liquids on Titan’s surface showed standing bodies of liquid would only exist at the poles, but one of the newly found “tropical” lakes appears to be about half the size of Utah’s Great Salt Lake, with a depth of at least 3 feet (1 meter).

Where could the liquid for these lakes come from? “A likely supplier is an underground aquifer,” said Caitlin Griffith, the paper’s lead author and a Cassini team associate at the University of Arizona, Tucson. “In essence, Titan may have oases.”

Understanding how lakes or wetlands form on Titan helps scientists learn about the moon’s weather. Like Earth’s hydrological cycle, Titan has a “methane” cycle, with methane rather than water circulating. In Titan’s atmosphere, ultraviolet light breaks apart methane, initiating a chain of complicated organic chemical reactions. But existing models haven’t been able to account for the abundant supply of methane.

“An aquifer could explain one of the puzzling questions about the existence of methane, which is continually depleted,” Griffith said. “Methane is a progenitor of Titan’s organic chemistry, which likely produces interesting molecules like amino acids, the building blocks of life.”

Global circulation models of Titan have theorized that liquid methane in the moon’s equatorial region evaporates and is carried by wind to the north and south poles, where cooler temperatures cause methane to condense. When it falls to the surface, it forms the polar lakes. On Earth, water is similarly transported by the circulation, yet the oceans also transport water, thereby countering the atmospheric effects.

The latest results come from Cassini’s visual and infrared mapping spectrometer, which detected the dark areas in the tropical region known as Shangri-La, near the spot where the European Space Agency’s Huygens probe landed in 2005. When Huygens landed, the heat of the probe’s lamp vaporized some methane from the ground, indicating it had landed in a damp area.

Areas appear dark to the visual and infrared mapping spectrometer when liquid ethane or methane are present. Some regions could be shallow, ankle-deep puddles. Cassini’s radar mapper has seen lakes in the polar region, but hasn’t detected any lakes at low latitudes.

The tropical lakes detected by the visual and infrared mapping spectrometer have remained since 2004. Only once has rain been detected falling and evaporating in the equatorial regions, and only during the recent expected rainy season. Scientists therefore deduce the lakes could not be substantively replenished by rain.

“We had thought that Titan simply had extensive dunes at the equator and lakes at the poles, but now we know that Titan is more complex than we previously thought,” said Linda Spilker, the Cassini project scientist based at NASA’s Jet Propulsion Laboratory, Pasadena, Calif. “Cassini still has multiple opportunities to fly by this moon going forward, so we can’t wait to see how the details of this story fill out.”

The findings appear in this week’s issue of the journal Nature.

Posted on by Jason Major

On the Edge of Titan

Titan's haze-covered limb seen by Cassini on June 6

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Here’s a quick look at one of my favorite cosmic photo subjects – the varying layers of atmosphere that enshroud Saturn’s enormous moon Titan. The image above is a color-composite made from three raw images acquired by Cassini during its latest flyby.

On June 7 Cassini approached Titan within 596 miles (959 km) and imaged portions of the moon’s northwest quadrant with its radar instrument, as well as conducted further investigations of areas near the equator where surface changes were detected in 2010.

The image here was assembled from three raw images captured in red, green and blue visible light channels. It reveals some structure in the upper hydrocarbon haze layers that extend upwards above the moon’s opaque orange clouds — reaching 400-500 km in altitude, Titan’s atmosphere is ten times thicker than Earth’s!

The June 6 flyby was the second in a series of passes that will take Cassini into a more inclined orbit, where it will reside for the next three years as it investigates Saturn’s polar regions and obtains better views of its ring system.

Read more about the flyby here.

Image: NASA/JPL/Space Science Institute. Composite by J. Major.

Posted on by Jason Major

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.)

Posted on by Jason Major

A New Angle on Titan

Color-composite image of Titan and Saturn. There are few confirmed craters on Titan, and the ones that have been spotted are much shallower than expected. Image Credit: 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)