APOD: Giant Dust Ring Discovered Around Saturn (2009 Oct 13)

[keshlam]

The insert graphic makes it appear that the new ring is orbiting on a significantly different plane than the others. True, or just a presentation artifact?

http://apod.nasa.gov/apod/ap091013.html

[Case]

The insert graphic makes it appear that the new ring is orbiting on a significantly different plane than the others. True, or just a presentation artifact?

True. Saturn's 'new' dust ring is tilted at about 27 degrees from the main ring plane.

[kovil]

"The new ring is canted 27 degrees from the main ring plane and is in a retrograde orbit around the giant gas planet. It is also quite large. As Anne Verbiscer from the University of Virginia commented: "This is one supersized ring. If you could see the ring, it would span the width of two full moons' worth of sky, one on either side of Saturn."

The vast belt of material ends at 18 million kilometers from the planet and is 12 million kilometers wide. It is also much thicker than the main rings: 2.5 million kilometers from top to bottom. The thickness measurement is an approximation, since the ring is so diffuse. "

Saturn the planet by contrast is 120,500 km in diameter and its rings are about 240,000 km in diameter, which makes Saturn the planet and its rings quite small compared to this newly discovered supersize me ring !

Seeing as how Saturn has, at latest count, 61 Moons, it is almost a 'solar system' unto itself !

I would lay odds that Saturn's electrical field and its interaction with the solar wind has something to do with this newly discovered 'plasma ring' !
It must be plasma, because it is 'glowing' in the infrared ! It also must have an electrical energy input in order to glow in the infrared.
Our task is to determine the electrical circuit that the Sun, Saturn, and the giant infrared glowing ring around Saturn, are making and why.

[On and edit]: Thanks Star*Hopper for the article link: http://science.nasa.gov/headlines/y2009 ... ntring.htm
"Spitzer's infrared eyes were able to spot the glow of the cool dust, which has a temperature of only about 80 Kelvin (minus 316 degrees Fahrenheit)."
? Would dust grain absorption of solar energy radiations be sufficient to account for an 80-K temperature of themselves, considering any ability they have to reradiate any energy ?

[additional edit]: The Variable Rotation Period of the Inner Region of Saturn’s Plasma Disk - 2007
D. A. Gurnett,1 A. M. Persoon,1 W. S. Kurth,1 J. B. Groene,1 T. F. Averkamp,1
M. K. Dougherty,2 D. J. Southwood2,3
We show that the plasma and magnetic fields in the inner region of Saturn’s plasma disk rotate
in synchronism with the time-variable modulation period of Saturn’s kilometric radio emission.
This relation suggests that the radio modulation has its origins in the inner region of the plasma
disk, most likely from a centrifugally driven convective instability and an associated plasma outflow
that slowly slips in phase relative to Saturn’s internal rotation. The slippage rate is determined
by the electrodynamic coupling of the plasma disk to Saturn and by the drag force exerted by its
interaction with the Enceladus neutral gas torus.

http://www.sciencemag.org/cgi/content/a ... 7/4429/407

You can sign up for free and access this article and many more in full.

[Star*Hopper]

This is somewhat surprising (the image APOD presents). I got news of this new discovery off one of my news feeds this past Wednesday, & seeing today's title opened it fully expecting to see the much better-depicting image shown here.
http://science.nasa.gov/headlines/y2009 ... ntring.htm
Even as an artist's concept, it displays much better the enormity & perspective of this remarkable discovery....makes the APOD shot kinda disappointing.

~S*H

[bstout]

I was puzzled by the inclination of the dust ring, too, and I wish the APOD description mentioned why it is tilted. But one of its links, http://www.universetoday.com/2009/10/07 ... nd-saturn/, does describe that the ring is caused by Saturn's moon Phoebe, and fits precisely with Phoebe's orbit. In fact, the scientists who found it were looking for it, suspecting that Phoebe's dust is the source of sister moon Iapetus's dark side. The article Star*Hopper links to also discusses this.

[neufer]

[On and edit]: Thanks Star*Hopper for the article link: http://science.nasa.gov/headlines/y2009 ... ntring.htm
"Spitzer's infrared eyes were able to spot the glow of the cool dust, which has a temperature of only about 80 Kelvin (minus 316 degrees Fahrenheit)."
? Would dust grain absorption of solar energy radiations be sufficient to account for an 80-K temperature of themselves, considering any ability they have to reradiate any energy ?

Yes.

• Earth's average radiative temperature = 250 K
  
  Average radiative temperature at 9.6 AU = 250/sqrt(9.6) = 81 K

Note: if the dust is as dark as the dark side of Iapetus then the temperature would be closer to 90 K

[neufer]

The insert graphic makes it appear that the new ring is orbiting on a significantly different plane than the others.

True?

True. Saturn's 'new' dust ring is tilted at about 27 degrees from the main ring plane.

The real truth (or truthiness?) is that since it is in retrograde
Saturn's 'new' dust ring is tilted at 153° from the main ring plane.

(Note: The axial tilt of Uranus is 97.77°)

[bystander]

Nice little video at http://www.spitzer.caltech.edu/Media/re ... uals.shtml
and the Spitzer PR at http://www.spitzer.caltech.edu/Media/re ... ease.shtml

[geckzilla]

Oh, I didn't know that one of them was a video. So used to flying by and scanning quickly through all this information available on the internet. I've been pronouncing Iapetus wrong in my head.

[Star*Hopper]

Ummmmmmmmmm............Direction of rotation has what to do with physical geometry, again?

The insert graphic makes it appear that the new ring is orbiting on a significantly different plane than the others.

True?

True. Saturn's 'new' dust ring is tilted at about 27 degrees from the main ring plane.

The real truth (or truthiness?) is that since it is in retrograde
Saturn's 'new' dust ring is tilted at 153° from the main ring plane.

(Note: The axial tilt of Uranus is 97.77°)

[geckzilla]

Art, you've confused another person with your quirky wit. How many external links and wikipedia articles is it going to take to clean this one up?

[bystander]

Ummmmmmmmmm............Direction of rotation has what to do with physical geometry, again?

Inclination - vertical tilt of the ellipse with respect to the reference plane, measured at the ascending node (where the orbit passes upward through the reference plane)

So retrograde inclinations would be 180° off from prograde. Similarly, Wiki lists Phoebe's inclination at 151.78°, not 28.22°.

[neufer]

The real truth (or truthiness?) is that since it is in retrograde
Saturn's 'new' dust ring is tilted at 153° from the main ring plane.

(Note: The axial tilt of Uranus is 97.77°)

Ummmmmmmmmm............
Direction of rotation has what to do with physical geometry, again?

Use the Van Gogh right hand grip rule.

[neufer]

Art, you've confused another person with your quirky wit.

Then I've done my job.

How many external links and wikipedia articles is it going to take to clean this one up?

Five.

<<For the FIFTH labor, Eurystheus ordered Hercules to clean up King Augeas' stables. Hercules knew this job would mean getting dirty and smelly, but sometimes even a hero has to do these things. Then Eurystheus made Hercules' task even harder: he had to clean up after the cattle of Augeas in a single day. Now King Augeas owned more cattle than anyone in Greece. Some say that he was a son of one of the great gods, and others that he was a son of a mortal; whosever son he was, Augeas was very rich, and he had many herds of cows, bulls, goats, sheep and horses.>>

[BMAONE23]

Sounds like there is a whole bunch of newly discovered stuff infesting Saturns orbit...Is it still a planet???

[orin stepanek]

Sounds like there is a whole bunch of newly discovered stuff infesting Saturns orbit...Is it still a planet???

It's a giant poofball.

Orin

[Star*Hopper]

But you're talkin' about the inclination of the ring to the planet, not the planet's inclination. The ring's in retro, not Saturn.

[bystander]

But you're talkin' about the inclination of the ring to the planet, not the planet's inclination. The ring's in retro, not Saturn.

See my post above which deals with orbital inclinations (moons, rings, etc)

[orin stepanek]

Art's cafe post adds to this discussion. http://asterisk.apod.com/viewtopic.php?f=8&t=17467 Nice find Art. 8)

Orin

[neufer]

The Phoebe ring
By Emily Lakdawalla Oct. 14, 2009

<<All it takes is one glance at Phoebe to know that a lot of it has been blasted away due to numerous impacts with other, smaller bodies. So it is no stretch at all to imagine that there should be material in Phoebe's orbit making a ring. Verbiscer and her coauthors predicted that there might be such a ring. But Phoebe's orbit is so incredibly large that this "ring" would be almost unimaginably sparse.

What happens to [these ring] particles depends upon their size. The biggest chunks, several centimeters in size or larger, don't really migrate anywhere, sticking around near Phoebe's orbit until they smack into something -- each other or Phoebe. The model simulation suggests that it would take more than the age of the solar system for half of the particles to be removed from the system by re-collision with Phoebe, so most of the biggest chunks are still out there somewhere in Phoebe's orbital space.

What about smaller particles? The article says "re-radiation of absorbed sunlight exerts an asymmetric force on dust grains, causing them to spiral in towards Saturn with a characteristic timescale of 150,000 x rg where rg is the particle radius in micrometers. This force brings all centimetre-sized and smaller material to Iapetus and Titan unless mutual particle collisions occur first....Most material from 10 micrometres to centimetres in size ultimately hits Iapetus, with smaller percentages striking Hyperion and Titan." This would be a slow process that has operated continuously since whenever Phoebe was captured into Saturn's orbit. There might have been bursts of material delivered to Iapetus associated with some of the bigger impacts that have left such large scars on Phoebe, but they would have been blips above a steady background.

Anyone who knows the first thing about Iapetus should be saying "Aha!" at this point. Iapetus, is, of course, known for being the yin-yang moon, whose leading hemisphere is dark and whose trailing hemisphere is bright. Cassini observations of Iapetus have proven that the dark material is almost certainly exogenous (coming from outside) rather than endogenous (coming from internal geologic activity). The small number of fresh, rayed craters on Iapetus shows that the darkening process is continuing today. The fact that the dark stuff only shows up on the leading hemisphere -- the side of Iapetus that faces forward in its orbit -- suggests that it's "sweeping up" the dark material, plowing into it as it moves in its stately path around Saturn. The side of Iapetus that faces backward along its orbit is in the lee of Iapetus' motion through the cloud of particles and doesn't sweep up the material.

It's long been suggested that Phoebe could be the source of this dark material. Verbiscer et al. go on to do some calculations that suggest that Phoebe material accumulates on Iapetus at a rate of about 40 micrometers per million years; over the age of the solar system that gives you 20 centimeters of material deposited on Iapetus. But because there were probably once a lot more distant kilometer-scale moons of Saturn that eventually crashed into Phoebe, the production rate of Phoebe ring material and therefore the Iapetus accumulation rate in the past was very likely higher, "leading to...a cumulative thickness of material on Iapetus that is probably measured in metres."

It's all a pretty neat picture. It doesn't even require Phoebe to have any kind of unusual geologic activity or unusually large past impacts -- all it needs to be is a big body sitting in its distant orbit, and other bodies in the Saturn system will crash in to it and create this supply of material that eventually impacts Iapetus. One question I haven't answered yet though is how come Phoebe has a ring if such structures haven't been seen around other moons? For instance, someone asked me, why isn't there a dust ring around the orbit of our Moon?

In a way, the way we are finding fainter and fainter rings is parallel to the way we're finding smaller and smaller moons. I'm pretty certain that there are a few motes more dust along our Moon's orbit than there is outside our Moon's orbit, but the Moon is so large, with such strong gravity, that nearly everything that is ejected from any impact on the Moon almost immediately returns to the lunar surface; no one will ever find a "ring" in the Moon's orbit.

Elsewhere in the solar system, as you look to smaller and smaller moons, you will see more and more dust associated with that moon's orbit. In the Saturn system, the Cassini mission is careful as the spacecraft crosses the orbits of all the medium-sized moons like Tethys, Dione, and Rhea, pointing the high-gain antenna forward along its path so that the antenna acts like an umbrella, shielding the more sensitive instruments from collisions with little dust particles.

Look at the even smaller moons Thebe and Amalthea at Jupiter, and there are definite "gossamer rings" associated with their orbits. Interestingly, Verbiscer et al. point out in their paper that Thebe and Amalthea are "far more prolific sources of debris" than Phoebe because their close location to Jupiter means that collisions are more energetic, but because the debris from collisions re-impacts Thebe and Amalthea very quickly, the optical depth of their associated rings is actually very similar to the optical depth of the Phoebe ring, even though the Phoebe ring is far larger; which means that the Phoebe ring contains thousands of times more material than the Thebe and Amalthea gossamer rings do.

The article concludes: "Although [its] exotic properties as well as its sheer size make the Phoebe ring unique among known planetary rings, similar structures should also adorn the other gas giant planets.">>