Posted on by Jason Major

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.

Posted on by Jason Major

Titan Shines in Latest Cassini Shots

Color-composite raw image of Titan’s southern hemisphere. Note the growing south polar vortex. (NASA/JPL/SSI/Jason Major)

Last Thursday, November 29, Cassini sailed past Titan for yet another close encounter, coming within 1,014 kilometers (603 miles) of the cloud-covered moon in order to investigate its thick, complex atmosphere. Cassini’s Visible and Infrared Mapping Spectrometer (VIMS), Composite Infrared Spectrometer (CIRS) and Imaging Science Subsystems (ISS) instruments were all busy acquiring data on Titan’s atmosphere and surface… here are a couple of color-composites made from raw images captured in visible light channels as well as some of the more interesting monochrome raw images. Enjoy!

The structure of Titan’s upper-level hazes, which extend ten times the height of Earth’s atmosphere. (NASA/JPL/SSI)

Cassini captured this view of Titan’s crescent during its approach, from a distance of 193,460 kilometers (NASA/JPL/SSI/Jason Major)

Cassini’s continuum filter (CB3) allows it to image Titan’s surface. The dark areas are vast fields of hydrocarbon sand dunes (NASA/JPL/SSI)

These images have not been validated or calibrated by NASA or the mission team.

Read more about the T-88 flyby here.

Posted on by John Williams

A Colorful and Unexpected Reversal at Titan

This artist’s impression of Saturn’s moon Titan shows the change in observed atmospheric effects before, during and after equinox in 2009. The Titan globes also provide an impression of the detached haze layer that extends all around the moon (blue). This image was inspired by data from NASA’s Cassini mission. Image Credit: ESA

A certain slant, or shift, of light glinting off of Saturn’s moon Titan turns out to drive unexpected reversals in the moon’s atmosphere according to data from NASA’s Cassini spacecraft.

In a paper released in the November 28, 2012 issue of the journal Nature, scientists say in a press release that data from Cassini show evidence for sinking air where upwelling currents were seen earlier in the mission.

“Cassini’s up-close observations are likely the only ones we’ll have in our lifetime of a transition like this in action,” said Nick Teanby, the study’s lead author who is based at the University of Bristol, England, and is a Cassini team associate. “It’s extremely exciting to see such rapid changes on a body that usually changes so slowly and has a ‘year’ that is the equivalent of nearly 30 Earth years.”

Of the eight planets and dozens of moons in our solar system, just Earth, Venus, Mars and Titan have both a solid surface and a substantial atmosphere.

Cassini offers scientists a unique perspective during this change of seasons. The pole experiencing winter is typically pointed away from Earth because of its orbit around Saturn. Cassini provides scientists a platform to watch the atmosphere change over time and study the moon from angles impossible from Earth. It arrived at the ringed planet in 2004. Models of Titan’s atmosphere have predicted changes for two decades but Cassini is just now seeing new circulation patterns arise.

“Understanding Titan’s atmosphere gives us clues for understanding our own complex atmosphere,” said Scott Edgington, Cassini deputy project scientist at NASA’s Jet Propulsion Laboratory, Pasadena, Calif. “Some of the complexity in both places arises from the interplay of atmospheric circulation and chemistry.”

While scientists recently have watched the formation of haze and a vortex over Titan’s south pole, other Cassini instruments, such as the composite infrared spectrometer (CIRS), have gathered data tied more to the circulation and chemistry of Titan’s orangish atmosphere especially at higher altitudes. The CIRS instrument also reveals subtle changes in vertical winds and global circulation. The instrument shows that atmospheric circulation extends about 100 km, or 60 miles, higher than expected. This is important in explaining the orangish tint to Titan’s atmosphere. A haze layer, first detected by Voyager 1, may be a region rich in small haze particles that combine to form larger aggregates that descend deep into the atmosphere giving the moon its characteristic color.

Scientists have narrowed down the atmospheric reversal to about six months near the August 2009 equinox when the Sun was shining directly on Titan’s equator.

“Next, we would expect to see the vortex over the south pole build up,” said Mike Flasar, the CIRS principal investigator at NASA’s Goddard Space Flight Center in Greenbelt, Md. “As that happens, one question is whether the south winter pole will be the identical twin of the north winter pole, or will it have a distinct personality? The most important thing is to be able to keep watching as these changes happen.”

Second image caption: This true color image captured by NASA’S Cassini spacecraft before a distant flyby of Saturn’s moon Titan on June 27, 2012, shows a south polar vortex, or a swirling mass of gas around the pole in the atmosphere. Image Credit: NASA/JPL-Caltech/Space Science Institute

Source: NASA/Jet Propulsion Laboratory

Posted on by Jason Major

Saturn’s Strange Hexagon – In Living Color!

Color-composite Cassini image of Saturn’s northern hexagon (NASA/JPL/SSI/Jason Major)

Cassini sure has been busy these past few days! After returning some mind-blowing images of the swirling 3,000-km-wide cyclone over Saturn’s north pole the spacecraft pulled back to give a wider view of the ringed giant’s upper latitudes, revealing one of its most curious features: the northern hexagon.

The image above is a color-composite made from raw images acquired by Cassini on November 28 from a distance of 379,268 miles (610,373 kilometers) away. Because the color channels were of a much lower resolution than the clear-filter monochrome image, the color is approximate in relation to individual atmospheric details. Still, it gives an idea of the incredible variation in hues around Saturn’s northern hemisphere as well as clearly showing the uncannily geometric structure of the hexagon.

(Can I get another “WOW”?)

Made of a band of upper-atmospheric winds, for some reason at this latitude the stream forms a six-sided hexagonal shape. The entire structure is about 25,000 km across — large enough for four Earths to fit inside! The polar cyclone can be seen at the very center.

First seen by Voyagers 1 and 2 over 30 years ago the hexagon appears to be fixed with Saturn’s rotation rate, which is a remarkably speedy 0.44 Earth-days (about 10.5 hours.)

“This is a very strange feature, lying in a precise geometric fashion with six nearly equally straight sides,” said atmospheric expert and  Cassini team member Kevin Baines back in 2007. “We’ve never seen anything like this on any other planet. Indeed, Saturn’s thick atmosphere where circularly-shaped waves and convective cells dominate is perhaps the last place you’d expect to see such a six-sided geometric figure, yet there it is.”

As scientists puzzled over the mechanisms behind the geometric feature, they came to the conclusion that not only is it a very natural occurrence, it’s also something that is not uncommon in fluid dynamics… apparently its sides are bound by the eddying storms. (Read more in this article by Nicole Gugliucci.)

Here are some more raw images from Cassini’s Nov. 28 pass:

Amazing! Here we are well over 8 years after arriving at Saturn and Cassini is still astounding us almost daily with views of the ringed world. (I knew it was my favorite planet for a reason!)

As always, stay tuned to Universe Today for more!

Image credits: NASA/JPL/Space Science Institute. Color-composite by Jason Major.

 

Posted on by Jason Major

Incredible Raw Image of Saturn’s Swirling North Pole

Ok, are you ready for this?

I know… WOW.

This swirling maelstrom of clouds is what was seen over Saturn’s north pole earlier today, November 27, by NASA’s Cassini spacecraft. This is a raw image, acquired in polarized light, from a distance of 238,045 miles (383,097 kilometers)… all I did was remove some of the hot pixels that are commonly found on Cassini images taken with longer exposures.

Again… WOW.

My attempt at a color composite can be seen below, plus another treat:

It’s rough, and a little muddy because the clouds were moving between image channels (not to mention the blue channel image was rather underexposed) but here’s a color-composite of the same feature, made from images taken from a slightly different perspective:

Color composite of Saturn’s north polar vortex

Pretty darn cool… Cassini does it yet again!

The images above show an approximately 3,000-4,000-km-wide cyclone above Saturn’s north pole. Saturn is also known to have a long-lived hexagonal jet stream feature around its north pole as well, but that is not shown in those images as it runs along a lower latitude. Instead, you can see that HERE:

Saturn’s northern hexagon

Captured with a wider angle, in this image the hexagon structure can be made out as well as the cyclone, which sits at the center just over the pole. Saturn’s hexagon is about 25,000 km (15,500 miles) in diameter… large enough to fit almost four Earths inside. This image was also acquired today.

An RGB composite of this feature is below:

Saturn’s northern hexagon – color composite

It’s been a few years since we’ve gotten such a good look at Saturn’s north pole… thanks to Cassini’s new orbital trajectory, which is taking it high above the ring plane and poles of Saturn, we now have the opportunity to view the gas giant’s dynamic upper latitudes again. I’m sure this is just a taste of what’s to come!

(Image credit: NASA/JPL/Space Science Institute. Color composites by Jason Major)

Posted on by Jason Major

Saturn. In color.

Color-composite of Saturn, made from raw Cassini images acquired in visible light channels on 18 Nov. 2012. (NASA/JPL/SSI. Composite by Jason Major.)

Looking for an awesome view of Saturn as it would look from 1,951,681 kilometers (1,212,718 miles) away? Here you go.

Just my and Cassini’s way of reminding everyone how beautiful our own Solar System is! Lest we forget.

Posted on by Jason Major

Saturn’s Fluctuating F Ring

Bright clumps of material spotted within Saturn’s ropy F ring (NASA/JPL/SSI)

Released today, this image acquired by NASA’s Cassini spacecraft shows some interesting structures forming within Saturn’s thinnest but most dynamic ring.

Of Saturn’s countless ring structures the F ring may very well be the most dynamic, if not the most fascinating. Orbiting Saturn just outside the edge of the A ring at a distance of 140,000 km (87,000 miles), the F ring is a hazy, ropy band of fine ice particles that shift, twist and occasionally gather into bright clumps… only to drift apart once more.

The F ring can range in width from 30 to 500 km (20-500 miles), depending on what’s going on in and outside of it.

The image above, originally captured by Cassini on June 28 and released today by the Cassini Imaging Central Laboratory for Operations (CICLOPS), shows a particularly bright clump of material at the outer edge of the F ring, as well as some finer structures and streamers forming within the inner bands. Due to the lighting geometry its thought that the clumps are mostly composed of dusty material.

Detail of the ghostly F ring structures (NASA/JPL/SSI)

The features seen here are likely due to the ring’s interactions with passing shepherd moons — such as the 148-km-wide Prometheus — or with small moonlets embedded within the ring itself. Mostly made of fine particles of dust and ice smaller than those found in smoke, the material orbiting within the F ring is extremely susceptible to external gravitational influences.

Original image scale is 4 km (3 miles) per pixel.

See more images from the entire Cassini mission on the CICLOPS site here (and for a look at more interesting ring dynamics check out these recent Cassini images of my personal favorite moon, Daphnis.)

 

Posted on by John Williams

Swirling Vortex and Mini Moons: Spectacular Views of the Little Things Around Saturn

High-altitude clouds in Titan’s seasonal south polar swirl glow dimly in this image from NASA’s Cassini spacecraft.

With wild storms and a vast ring system, nothing seems small around Saturn. But as NASA’s Cassini spacecraft loops high over Saturn’s poles, scientists are taking time to explore the little things including a swirling vortex, the miniature moon Mimas, and another tiny ovoid moon named Methone.

Titan’s swirling vortex, lower right, glows brightly against the south polar clouds in this new image from NASA’s Cassini spacecraft. Scientists are monitoring the development of the swirling mass of gas to try and understand the weather related to the coming winter to the moon’s south pole. For a color closeup of the vortex, see Titan’s Colorful South Polar Vortex. If you’re more into a moving visualization, check out the vortex in motion.


Cassini acquired the view of the vortex on Titan on August 31, 2012 using a special filter sensitive to light in the near-infrared. Cassini took this image from a distance of about 1.2 million kilometers (750,000 miles) above the south pole of Titan. That’s nearly three times the distance between Earth and the Moon. The smallest detail on this image is about 4 miles across.

“Note the motions and beautifully detailed cloud patterns,” wrote Carolyn Porco, Cassini imaging team lead on the CICLOPS website, “very likely the result of open-cell convection — already visible in this fascinating phenomenon that we on Cassini have been fortunate to capture, for the first time, in the process of being born.”

Methone looks like a tiny gray egg in this image from NASA’s Cassini spacecraft.

Last week, the Cassini imaging team released two stunning images of Saturn. Tiny, egg-shaped Methone (pronounced meh-tho-nee) is barely 3 kilometers (2 miles) across. Cassini discovered this moon in 2004 hanging out between Mimas and Enceladus at just 194,000 km (120,000 miles) above Saturn. From Methone’s smooth surface, Saturn must be a true wonder. Small moons like Methone are generally non-round. Scientists believe they just don’t have the mass to pull themselves together into a round shape. The leading side of Methone is lit in this image and at a distance of just 4,000 km (2,500 miles) the smallest feature that can be seen is about 27 meters (88 feet).

Saturn’s moon Mimas is dwarfed by Saturn and its rings in this spectacular image from NASA’s Cassini spacecraft

Don’t blink or you might miss a tiny dot just to the upper left of Saturn. Mimas is dwarfed not only by Saturn’s rings, but also by the gigantic storms visible in the northern and southern hemisphere’s Mimas is just 396 km (246 miles) across and is the solar system’s 20th largest satellite. The moon could easily fit within the borders of Spain and most western states in the U.S. Cassini took this spectacular image from a distance of 2.4 million kilometers (1.5 million miles) from Saturn.

Source: NASA Jet Propulsion Laboratory and Cassini Imaging Central Laboratory for Operations (CICLOPS)

Posted on by Jason Major

Cassini Discovers Titan’s Glowing Atmosphere

A pair of images from NASA’s Cassini spacecraft show Titan glowing in the dark.

Titan never ceases to amaze. Saturn’s largest moon, it’s wrapped in a complex, multi-layered nitrogen-and-methane atmosphere ten times thicker than Earth’s. It has seasons and weather, as evidenced by the occasional formation of large bright clouds and, more recently, an area of open-cell convection forming over its south pole. Titan even boasts the distinction of being the only other world in the Solar System besides Earth with large amounts of liquid existing on its surface, although there in the form of exotic methane lakes and streams.

We have NASA’s Cassini spacecraft to thank for these discoveries, and now there’s one more for the ceaseless explorer to add to its list: Titan glows in the dark.

Seen above in two versions of the same calibrated raw image, acquired by Cassini on May 7, 2009, Titan hovers in front of a background field of stars which appear as blurred streaks due to the 560 seconds (about 9 1/2 minutes) exposure time and the relative motion of the spacecraft.

The image on the left shows Titan in visible light, receiving reflected sunlight off Saturn itself — “Saturnshine” — while the moon was on the ringed planet’s night side. The image on the right was processed to exclude this reflected light… and yet it still shines. (E pur si candeo?)

Read: Titan’s Surface “the Consistency of Soft, Damp Sand”

The hazy moon’s dim glow — measuring only around a millionth of a watt — comes from not only the top of its atmosphere (which was expected) but also from much deeper within, at altitudes of 300 km (190 miles).

The glow is created by chemical reactions within Titan’s atmosphere, sparked by interactions with charged particles from the Sun and Saturn’s magnetic field.

“It turns out that Titan glows in the dark – though very dimly,” said Robert West, the lead author of a recent study in the journal Geophysical Research Letters and a Cassini imaging team scientist at NASA’s Jet Propulsion Laboratory. “It’s a little like a neon sign, where electrons generated by electrical power bang into neon atoms and cause them to glow. Here we’re looking at light emitted when charged particles bang into nitrogen molecules in Titan’s atmosphere.”

The light is analogous to the airglow seen in Earth’s atmosphere, often photographed by astronauts aboard the ISS.

Still, even taking known sources of external radiation into account, Titan is glowing from within with an as-yet-unexplained light. More energetic cosmic rays may be to blame, penetrating deeper into the moon’s atmosphere, or there could be unexpected chemical reactions or phenomena at work — a little Titanic lightning, perhaps?

“This is exciting because we’ve never seen this at Titan before,” West said. “It tells us that we don’t know all there is to know about Titan and makes it even more mysterious.”

Read more on the Cassini mission page here, and see more images from Cassini on the CICLOPS imaging center site.

Images: NASA/JPL-Caltech/Space Science Institute. Inset image: Titan’s atmosphere and upper-level hydrocarbon haze, seen in June 2012. Color composite by J. Major.

Posted on by Nancy Atkinson

Giant “Invisible” Vortex Still Remains on Saturn Following Huge Storm

In 2010, a small, bright white storm emerged on Saturn’s northern hemisphere. This storm grew until it wrapped around the planet in curly cloud structures, creating a colossal atmospheric disturbance that endured into the early part of 2012, becoming the largest storm seen on the planet since 1990. Being in orbit around the ringed planet, the Cassini spacecraft had a front row seat to watch the disturbance unfold, allowing planetary scientists an unprecedented look at this monster storm. While the storm was visible even to amateur astronomers on Earth, much of its activity took place beyond the reach of visible-light cameras and telescopes, astronomers say. Not only did huge “beacons” of hot air chase each other around the planet, but infrared observations show a giant oval vortex is still persisting as a side effect from the storm.


“It’s the first time we’ve seen anything like it on any planet in the Solar System,” said Leigh Fletcher from the University of Oxford, UK, lead author of a paper describing the unprecedented storm. “It’s extremely unusual, as we can only see the vortex at infrared wavelengths – we can’t tell that it is there simply by looking at the cloud cover.”

Fletcher and her team also used ground-based observations with the Very Large Telescope of the European Southern Observatory in Chile, and NASA’s Infrared Telescope Facility at the summit of Mauna Kea in Hawaii.

As the visible storm erupted in the roiling cloud deck of Saturn’s troposphere, waves of energy rippled hundreds of kilometers upwards, depositing their energy as the two vast ‘beacons’ of hot air in the stratosphere.

Data from Cassini’s composite infrared spectrometer (CIRS) instrument revealed the storm’s powerful discharge sent the temperature in Saturn’s stratosphere soaring 65 degrees C (150 degrees Fahrenheit, 83 kelvins) above normal.

Researchers described in a complimentary paper that will be published in the Nov. 20 issue of the Astrophysical Journal this as a “belch” of energy, as they observed a huge increase in the amount of ethylene gas in Saturn’s atmosphere, the origin of which is a mystery. Ethylene, an odorless, colorless gas, isn’t typically observed on Saturn. On Earth, it is created by natural and man-made sources.

Researchers are still is exploring the origin of the ethylene, but they have ruled out a large reservoir deep in the atmosphere.

“We’ve really never been able to see ethylene on Saturn before, so this was a complete surprise,” said Goddard’s Michael Flasar, the CIRS team lead.

The beacons were expected to cool down and dissipate, but by late April 2011 – by which time bright cloud material had encircled the entire planet – the hot spots had merged to create an enormous vortex that for a brief period exceeded even the size of Jupiter’s famous Great Red Spot.

The forceful storm generated unprecedented spikes in temperature and increased amounts of ethylene. In these two sets of measurements taken by Cassini’s composite infrared spectrometer, yellow represents the highest temperatures. Each strip maps a single molecule (top: methane, bottom: ethylene), with temperature measurements taken in the northern hemisphere, all the way around the planet. Image credit: NASA/JPL-Caltech/GSFC

Although comparisons to Jupiter’s Red Spot have been made to this storm, Saturn’s storm was much higher in the atmosphere while Jupiter’s vortex is embedded deep down in the turbulent ‘weather zone’, Fletcher said.

Also, Jupiter’s famous vortex has raged for at least 300 years. But after traversing the planet once every 120 days since May 2011, Saturn’s large beacon is cooling and shrinking. Scientists expect it to fade away completely by the end of 2013.

The question now remains as to whether Saturn’s storm-generating energy has been sapped or if there will be a repeat performance, the team said.

The outburst already caught observers by surprise by arriving during the planet’s northern hemisphere spring, years ahead of the predictably stormy summer season.

“The beauty is that Cassini will be operating until the Saturn system reaches its summer solstice in 2017, so if there is another global event like this, we’ll be there to see it,” says ESA’s Cassini project scientist Nicolas Altobelli.

Sources: JPL, ESA, NASA