Saturn Archives

February 1, 2008December 26, 2015 by Nancy Atkinson

Cassini Finds Patterns and Rhythm in Saturn’s Rings

Cassini has been orbiting around Saturn for almost four years, and amazingly, the spacecraft keeps discovering new and unexpected features about this world and its system of rings and moons. Recently, in two of Saturn’s rings, Cassini found orderly lines of densely grouped, boulder-size icy particles that extend outward across the rings like ripples from a rock dropped in a calm pond. Surprisingly, the distances between these ring particles stay relatively equal even though their velocities may change. This type of pattern is completely new, as normally, the distances between particles change with their velocity.

The pattern was detected when Cassini sent out three signals toward Earth. The signals crossed Saturn’s rings, and the frequencies were scattered from the passing ring particles. Once the signals were captured by Earth-based antennas of NASA’s Deep Space Network, Cassini scientists saw a regular pattern in the received signal frequencies.

“This particular feature is the smallest and most detailed of anything seen in Saturn’s rings so far,” said Cassini radio science team member Essam Marouf. “In the chaotic environment of the rings, to find such regularity in the most cramped areas is nothing short of amazing.” The regular structure can only be found in locations where particles are densely packed together, such as the B ring and the innermost part of the A ring. The signals were sent to capture a complete view of the rings.

The unexpected pattern within Saturn’s rings may give scientists some new ideas of what to expect from other similar planets and solar systems.

Scientists call this pattern of particles “enormously extended natural diffraction grating.” A diffraction grating has parallel lines like a picket fence; when light hits this fence, it separates according to wavelength, from ultraviolet to infrared light.

“The signals showed that the particle groups were arranged in an unexpectedly regular formation that had rhythm within the rings of Saturn,'” said Marouf. “Each particle is in its own orbit, and sometimes they collide and move apart as their velocities change. As a result, you have particles bunched together into dense groups that extend across the ring in harmony with each other.”

Original News Source: Cassini Press Release

January 31, 2008December 26, 2015 by Fraser Cain

Global Map of Iapetus

Here’s a cool global map of Saturn’s moon Iapetus, stitched together from the various Cassini flybys. Cassini didn’t see the entire moon, so the imaging team put in photographs from Voyager to cover the missing polar regions.

You can see its distinct equatorial ridge on the left-hand side of the image, and the mottled dark and light patches that give the moon its Yin-Yang look. The image scale is 803 km per pixel.

It’s a little old, but check out this video of the most recent Cassini Iapetus flyby back in September 2007.

Original Source: NASA/JPL/SSI News Release

January 8, 2008December 26, 2015 by Nicholos Wethington

Matching Cyclone Found at Saturn’s North Pole

Cassini keeps on brining us surprises from Saturn and its moons. Recently, it helped us narrow down the length of a day on Saturn. Now, infrared data from the spacecraft confirms a hot, hexagonal cyclone spinning away at the north pole of of the planet.

The south polar hot spot had been previously observed, and was thought to be due to the sunny conditions, as this region of Saturn is currently in summer. Observations from the Cassini spacecraft in early 2007 revealed that Saturn also has a hot cyclone spinning away at the north pole, despite the fact that this region hasn’t seen the Sun in over 10 years.

Voyager 1 and 2 took observations of the north pole in the 1980s, but the Cassini data gives a more detailed view of the features. It was thought that the sunlight was causing the hot spot at the south pole.This new data, though, adds a bit of mystery to the mechanisms causing the cyclones. They appear to be permanent fixtures of the planet, rather than caused by the seasons.

“The hot spots are the result of air moving polewards, being compressed and heated up as it descends over the poles into the depths of Saturn. The driving forces behind the motion, and indeed the global motion of Saturn’s atmosphere, still need to be understood,” said planetary scientist Leigh Fletcher of the University of Oxford, England, and lead author of the paper published in Science on January 4th.

The northern cyclone also has the peculiar shape of a hexagon, something absent from the southern cyclone. The recent findings place the hexagon higher up in the clouds than previously shown, though the cause of the curious shape is still unexplained.

Neptune is home to a hot spot on its southern pole, and the Great Red Spots on Jupiter is another example of long-lasting cyclonic features on a gas giant. Knowing more about the cyclones on Saturn will help us understand similar weather patterns on the other gas giants.

Winter lasts 15 years on Saturn, and in the next few years the north pole will again start to see sunlight, possibly changing the features of the cyclone and giving scientists a better understanding of how the Sun affects these tricky twisters.

Source: JPL Press Release

December 21, 2007December 26, 2015 by Nicholos Wethington

How Long is a Day on Saturn?

If you were on the surface of Saturn, how long would a day last? This has remained a mystery for scientists, because the thick clouds of gas obscure the surface of the planet from direct observation by telescopes or orbiters. Below all those clouds there is a surface that rotates at a constant speed. Since scientists can’t directly see the surface, they’ve taken another approach: listening.

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

With the help of radio emissions that come from the interior of Saturn, scientists have been able to close in on its rotation period. Charged particles trapped in the interior emit radio waves when they interact with Saturn’s magnetic field, at about 100 Kilohertz. It’s as if Saturn had its own radio station broadcasting at a certain frequency, and as the magnetic field deep inside the planet rotates it changes the frequency of the station.

Voyager measured these emissions for nine months when it passed by in the 1980s, and the rotation was calculated to be 10 hours 39 minutes 24 seconds, with an uncertainty of 7 seconds. The Ulysses spacecraft also monitored the emissions 15 years later, and came up with a result of 10 hours 45 minutes 45 seconds, with a 36 second margin of error.

Wait, that’s 6 minutes of difference! Either Saturn slowed down a lot over the years, or something else is going on. Cassini has been measuring these same radio emissions with its Radio and Plasma Wave Science instrument, and has observed that in addition to this long-period variation, the rotation differs by as much as one percent in a week.

Scientists think that this could be due to two different things: the solar wind coming from the Sun is interfering with the measurements, or particles from Enceladus’ geysers are affecting the magnetic field. Both of these would cause the radio emissions to vary, and they could be causing the different results simultaneously.

Cassini’s new data strongly suggests that the solar wind is a likely culprit: there is a variation in the measurements of the short-period rotation every 25 days, which corresponds with the rotation of the Sun as seen from Saturn. The speed of the solar wind, too, varies the measurements, so must be accounted for. Enceladus could be the cause of the long-term difference, but more measurements are needed to see if this is definitely the case, or if there is yet another factor.

Nailing down the rotation of Saturn will be helpful in calculating the true wind speeds of the clouds, and give important clues about the composition and distribution of the interior. Once the interference from the solar wind and Enceladus are taken into account, the true rotation of Saturn can be determined precisely.

Then only one question remains: do they have commercials on Saturn FM?

Source: ESA News Release

December 18, 2007December 26, 2015 by Nancy Atkinson

Enceladus: Cold Moon With a Hot Spot

enceladusfountains_med.thumbnail.jpg — Geysers spew from Enceladus in this image from the Cassini spacecraft. Credit: NASA/Cassini mission.

Saturn’s tiny moon Enceladus is a cold and icy place. But somehow, there’s enough heat being generated on Enceladus’ south pole to eject plumes of ice and vapor high above the moon. These plumes are extremely intriguing to the Cassini mission scientists and they want to know more about this hot spot on a very cold moon. In fact, Enceladus has become a major priority for study by the Cassini team and they are anticipating learning more about the moon in an upcoming fly-by.

The temperature at Enceladus’ south pole is about -220 degrees Celsius, but the hot spot is at least 100 degrees warmer. The leading model for the cause of the plumes on Enceladus is that the moon’s tides cause its crust to ratchet, or rub back and forth, in a set of faults near the south pole. The forces between Enceladus, the big planet Saturn and another moon, Dione cause what’s called dynamical resonance, and Enceladus is continually squeezed under this gravity field. This process creates a small hot spot, in relative terms, for an icy satellite.

Cassini has actually flown through the plumes, giving scientists a glimpse of the plume’s make-up.

“The plume particles are like smoke, ice smoke,”said William B. McKinnon, professor of earth and planetary sciences at Washington University in St. Louis. “If you were standing on Enceladus’ surface you wouldn’t even be able to see the plumes. The particles are just larger than the wavelength of light, about one-thousandths of a millimeter. Most icy bodies of this size are geologically inert, but this is a clear indication of geological activity. Cassini has found active venting of water vapor. This leads to scientifically intriguing speculations and questions.”

The scientists are pondering if Enceladus has active ice volcanism, and if so, is it due to ice sublimating, like a comet, or due to a different mechanism, like boiling water as in Old Faithful at Yellowstone. Even though there may be water on the moon, McKinnon doesn’t believe there is the possibility of life on Enceladus. This is because measurements made from Earth don’t indicate there is enough sodium present in the plumes to warrant the “life” question.

“The emerging view is that there’s not obvious evidence for a subterranean ocean in contact with rock, no boiling or venting,” said McKinnon.

The Cassini science team has made Enceladus a major priority and there will be seven additional close fly-bys of the moon by the spacecraft through mid-2010 (provided the mission is extended to that period.) The next fly-by will be on March 8, 2008 and Cassini will approach Enceladus at an incredibly close 25 km in altitude at the low latitudes and fly over the south pole at 580 km altitude. The spacecraft will actually fly through the plumes and should be able to take high-phase images of the plumes, map the temperatures of that region, search for any activity at other latitudes as well as image other interesting features on Enceladus, such as “tiger-stripe”-like fissures found near the south pole.

“We still can’t say how truly ‘hot’ the hot spots are,” said McKinnon. “We’ll probably learn this in March.”

Original News Source: Washington University Press Release

December 14, 2007December 26, 2015 by Fraser Cain

Saturn’s Rings Could Be as Old as the Solar System

Although the Solar System is 4.5 billion years old, planetary scientists thought that Saturn’s famous rings formed much later. Maybe as recently as a few hundred million years ago. But new observations from Cassini have pushed those estimate back… way back. Maybe all the way back to the beginning of the Solar System. Saturn’s rings might be ancient, with ring material getting recycled for eons.

According to Larry Esposito, principal investigator for Cassini’s Ultraviolet Imaging Spectrograph at the University of Colorado, Boulder, earlier data gathered by NASA’s Voyager spacecraft in the 1970s, and later from the Hubble Space Telescope indicated that the rings were young. Maybe a comet shattered one of Saturn’s moons about 100 million years ago, generating the particles we see today.

But the new evidence from Cassini shows the the rings vary in age significantly; the rings are being constantly replenished and recycled.

“The evidence is consistent with the picture that Saturn has had rings all through its history,” said Esposito. “We see extensive, rapid recycling of ring material, in which moons are continually shattered into ring particles, which then gather together and re-form moons.”

“We have discovered that the rings probably were not created just yesterday in cosmic time, and in this scenario, it is not just luck that we are seeing planetary rings now,” said Esposito. “They probably were always around but continually changing, and they will be around for many billions of years.”

So how can Cassini tell that there’s new material being generated. Astronomers used to think that infalling meteoric dust should pollute the older rings, making them darker. But the new Cassini observations show that the ring system spreads the pollution around, diluting it. This is why the rings appear to be so pristine and young.

They observed how the ring material blocked light from distant stars. They were able to detect 13 objects in Saturn’s F ring, varying in size from 27 metres to 10 kilometres (30 yards to 6 miles). Since most of the objects are translucent, the researchers think they’re just temporary clumps of icy boulders.

They appear to come and go, clinging together and then breaking apart under Saturn’s strong gravity. Although the rings always look the same, they’re being constantly recycled.

Original Source: NASA/JPL News Release

November 6, 2007December 26, 2015 by Fraser Cain

Podcast: Saturn’s Moons

We know that delaying this show one more week would be too dangerous, so here you go: Saturn’s moons. These are some of the most interesting objects in the Solar System, from the spongy Hyperion, to the geysers on Enceladus, to the rainy, misty, oceany Titan. They’ve kept Cassini busy for years, and scientists will likely be pondering them for decades.
Click here to download the episode

Saturn’s Moons – Show notes and transcript

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October 22, 2007December 26, 2015 by Astronomy Cast

Podcast: Saturn

Returning to our tour of the solar system, let’s voyage away from the largest planet to the second largest, Saturn. Once again, we’ll break up our visit because there’s lots to talk about. This week, we talk about Saturn and its famous rings. Next week, we’ll discuss its many moons.
Click here to download the episode

Saturn – Show notes and transcript

Or subscribe to: astronomycast.com/podcast.xml with your podcatching software.

October 11, 2007December 26, 2015 by Fraser Cain

Lakes in Titan’s Northern Polar Region

NASA’s Cassini spacecraft has now mapped out 60 percent of Titan’s north pole region, and it’s looking downright aquatic. At least 14% of the region revealed by Cassini is covered in what look like liquid hydrocarbon lakes. Take a look at the photo associated with this story, see the dark black regions? Those are lakes. But not lakes like we see them here on Earth.

The new images were mapped out by Cassini’s radar instruments, which can detect the smoothness of the surface of Titan. Extremely smooth sections are thought to be a liquid, while the bumpier regions are solid ground. The largest sea discovered so far has a surface area of 100,000 square kilometres (40,000 square miles), bigger than Lake Superior here on Earth.

Planetary scientists think the seas are filled with liquid ethane, methane and dissolved nitrogen. So far, more than 400 separate bodies of liquid have been discovered.

Original Source: NASA/JPL/SSI News Release

October 10, 2007December 26, 2015 by Nicholos Wethington

The Tiger Stripes and Geysers are Linked on Enceladus

Saturn’s moon Enceladus is one of the most peculiar objects in the Solar System. We now know there are geysers of water ice blasting from its southern pole; a place marked with long gashes that researchers have dubbed “tiger stripes”. Ever since the geysers were first discovered, scientists have been puzzling out their source. Now they understand how the geysers and tiger stripes are linked.

New research by the Cassini imaging team, CICLOPS, shows that the jets of Enceladus emanate from its southern pole, pouring out of four of the tiger stripes. The researchers have named them Alexandria, Cairo, Baghdad and Damascus. Of the four, Baghdad and Damascus are the most active and Alexandria is the least.

By taking Cassini’s two-year observations of the jets that spray from the surface, and combining this with thermal imaging of the stripes, the team was able to determine that the jets were spraying vertically out of the stripes, which are cracks on the surface of Enceladus.

The water sprays through the cracks because the gravity of Saturn pulls and pushes on Enceladus, and this motion – called a tidal force – heats up the frozen water underneath the surface. Much like geysers on Earth, the water is heated and expands below the surface, and follows the easiest path it can find to escape; this path happens to be right through the tiger stripes on the surface.

The researchers noted that when the tidal pull of Saturn was compressing this region of Enceladus, the geysers were not very active, if at all. But when the tides pulled and created tension, they began to erupt. Also, the hotter the region was, the stronger and larger the jet plume tended to be.

There may be other areas of Enceladus capable of producing jets, and now that the origins of the geysers are confirmed, more thermal and digital imaging of the surface could reveal other geysers in the future.

The researcher paper, entitled “Association of the jets of Enceladus with the warmest regions on its south-polar fractures” was published in the October 11th edition of the journal Nature.

Source: Nature