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NASA / JPL / SSI
Spiky vertical structures rise as high as 1.6 miles (2.5 kilometers) above the plane of Saturn's rings, as seen in an image captured by the Cassini orbiter two weeks before the planet's equinox in August 2009. Scientists believe the spikes are the result of a "splash effect" created by moonlets on the outer edge of Saturn's B ring.
The scientists behind the Cassini mission to Saturn say they have figured out the reasons behind the irregularities in the behavior of the most dynamic regions in Saturn's rings. They're due to a combination of natural oscillations that are amplified by the motions of the ring particles themselves -- plus an extra disturbance created by the moon Mimas.
The scientists also have discovered two regions within the rings that are the likely homes of moonlets yet to be discovered.
The lessons gained by watching the rings can also be applied to understanding how planetary systems and galaxies work, said Carolyn Porco, leader of Cassini's imaging team at the Colorado-based Space Science Institute.
"We have found what we hoped we'd find when we set out on this journey with Cassini nearly 13 years ago: visibility into the mechanisms that have sculpted not only Saturn's rings, but celestial disks of a far grander scale, from solar systems like our own all the way to the giant spiral galaxies," Porco said in a news release issued today.
Porco and Joseph Spitale, another member of the imaging team, are the authors of a report detailing the findings, published online today in The Astronomical Journal. The report is based on more than four years' worth of observations from the Cassini spacecraft, which has been orbiting Saturn since 2004.
What's causing the waves?
Those observations tracked the in-and-out oscillations of the planet's massive B ring, which you can see in this video on the imaging team's website, as well as this one. The shape of the B ring is controlled to some extent by Mimas -- but there are some extra wave patterns that weren't previously explained. Spitale and Porco say no fewer than three of the wave patterns spontaneously arose in part because the ring is dense enough, and the edge of the ring is sharp enough, for "free" waves to grow on their own and then reflect at the edge.
"These oscillations exist for the same reason that guitar strings have natural modes of oscillation, which can be excited when plucked or otherwise disturbed," Spitale said in the news release. "The ring, too, has its own natural oscillation frequencies, and that's what we're observing."
Such oscillations are thought to play a role in the motions of spiral galaxies as well as the dusty disks that give rise to planets, but because the oscillations can't be observed directly in those disks, they could only be inferred on the basis of computer simulations. Now astronomers have actually spotted large-scale wave patterns at work in the cosmos.
Peter Goldreich, a planetary ring theorist at Caltech, said the new findings show how the material in the densest parts of Saturn's rings can amplify oscillations and explain the "mysterious grooves first seen in images taken by the Voyager spacecraft" in the 1980s.
What's causing the spikes?
In addition to the self-excited oscillations, Cassini's scientists noticed disturbances in two regions on the B ring's outer edge, including spiky vertical structures that rise as much as 1.6 miles (3.5 kilometers) above the ring plane. One of the perturbed regions, measuring 12,000 miles (20,000 kilometers) in length, can be seen rolling around the edge of the B ring about halfway through this video clip.
NASA / JPL / SSI
A chevron-shaped disturbance can be seen along the outer edge of the B Ring, toward the top of this picture from the Cassini orbiter. Click to watch a QuickTime video of the disturbance rolling along the ring's edge.
The two disturbed areas -- known as Region A and Region B -- are not thought to be caused by the natural oscillations or by a previously known pattern linked to Mimas. Instead, the best explanation is that the regions contain moonlets measuring as much as a half-mile (1 kilometer) wide, or even wider.
"These objects may have been strewn across the outer B ring in the past, but migrated across the rings to become trapped in the Mimas resonance that maintains the B ring's outer edge," Porco told me in an e-mail.
As icy particles in the B ring pass by the moonlets, they "splash" upward from the closely packed ring plane to form the spiky peaks. The moonlets themselves have gone largely unseen. But the Cassini team did spot a moonlet embedded in the B ring last year, thanks to its shadow, and "propeller moons" have been detected in Saturn's A ring, which is outside the B ring. So scientists surmise that more moonlets should exist in Regions A and B.
In today's "Captain's Log" for the Cassini mission, Porco said the migration of the moonlets within the rings may mimic "the migration of the planets across the solar nebula in the early dawn of our solar system."
"All in all, we have here a fascinating story of physical mechanisms at work in Saturn's rings that are at work today, and have been in the past, in other disk systems throughout the cosmos," she said. "In other words, we have uncovered one single physical mechanism that has the power to explain simultaneously a host of seemingly unrelated phenomena ... just the kind of discovery we scientists love to make."
Correction for 4 p.m. ET Nov. 2: An earlier version of this posting erroneously said that the paper by Spitale and Porco appeared in The Astrophysical Journal instead of The Astronomical Journal.
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The long icy peak structure looks like a train rolling around the outer B ring. The mimas resonance is 2:1 BTW. So I guess that means 2 orbits around the B ring while the ring itself does 1 orbit. What is the orbital period of the B ring or Mimas for that matter?
I also can't get beyond how it looks like a vinyl 33-1/3 RPM record going around.
It does, doesn't it. just a bit warped.
Maybe we should play it and see what's on it! It might be a giant Voyager message.
I don't know. .anyone have a lp player anymore?
NASA, at the next equinox, capture a video of this!
Didn't Nasa find, that Saturns Rings actually make some very unusual sounds. Its a message from the ET's. or it could just be naturally occuring. Question though can there be sound in space? probably not the kind of sound we can hear, since space is a vacumn
Good question. Made me do a little looking.
According to the sources I looked up, technically, sound as we hear it can not travel through a vacume because sound waves need something to bounce off to travel. . some kind of particles or such.
That brings us to this question. If we continue our venture into deeper space. . .how will the pioneers keep in touch with the home world until relay stations can be built?
Radio waves, not sound waves, are used for communications. They just take forever to get back "home" and become fainter and fainter with distance. So, repeaters would certainly help with comms.
If I am correct, there are still radio signals coming from Voyager. I'm just not sure they are still being monitored but, this web site seems to imply that the monitoring may still be on-going: http://www.nasa.gov/mission_pages/voyager/voyager20101029.html
Launched in 1977, the Voyager missions are high on my list of our greatest accomplishments in exploring space.
And they are still phoning home!
Voyager 2 is right now 93.7 AU's* from Earth, moving away from us at the dizzying speed of 15.5 kilometers per SECOND! (That's 9.6 miles per second).
Voyager 1 is the distance and speed champ, though - she's 115.2 AU's out, hauling butt at 17.1 km/sec (10.6 miles/sec)!
(An AU is an Astronomical Unit, the average distance from the Earth to the Sun, and the standard unit for measuring distance in a solar system. Earth is 1 AU from the Sun, Pluto is an average of almost 40 AU's out, so Voyager 1 is nearly three times further away than Pluto. If you prefer miles rather than AU's, Voyager 1 is 10.67 billion miles (17.17 billion kilometers) away.)
Both Voyager 1 & 2 visited Jupiter and Saturn. Voyager 1 had a close flyby of Titan (Saturn's monster moon) and then headed for the edge of the Solar System. Voyager 2 is a bit slower as it's path also took it by Uranus and Neptune - the only mission to ever visit those two worlds.
Here's another way to visualize the distance, and the communication challenge. Every time NASA's Deep Space Network (the monster radio dishes that talk to missions all over the Solar System), says to Voyager 1 "How are you today?", it takes - even at the speed of light - just under 32 hours to get the reply ("I'm cold - can I come home now?).
The Voyagers are now into their "interstellar mission", mapping the extent of the Sun's heliosphere - the boundary where the solar wind is stopped by the interstellar medium - what I consider to be the edge of our Solar System.
The signal at that distance is incredibly weak by the time it gets back to us. You can do a search on "the inverse square law" to see why, but the short version is that signal strength goes down by the square of the distance.
(Example: let's say that, to make up a number, that when Voyager was 1 AU away we'd detect it's signal as 100 watts. Twice as far - 2 AU's - the signal strength has dropped to 25 watts. Ten times as far - 10 AU's, the distance to Saturn, and we are now only getting 1 watt. 100 AU's out - the edge of the Solar System - and we are trying to pick a signal that is only 1/10,000 of a watt. THAT's why radio dishes for astronomy are so huge - they are trying to capture a snowflake's worth of energy, and discern that tiny tiny signal against the roar of background noise.)
The Voyagers are powered by plutonium (do a search on "RTG" to see how that's done). It's hoped that they will still be functioning, and telling us more about the outer edge of our Solar System, for another 30 or so years.
The Voyagers are our first missions to head in the direction of the stars. It will take ~50,000 years to reach the next star at that speed, but it's a start!
Go Voyagers!
~Michael (AFM*Radio / Astronomy.FM)
Voyagers are expected to last until around 2025, and that will be the last of the instuments to go. Some other instruments have already gone offline and others will between now and then.
Thank you all for this information. it was all very enlightening. . .
It is amazing that Voyagers are still going strong. . .hopefully the information they send will help on further space explorations whenever they are reistitutionalized, since for now our government does not seem interested in a space program anymore which I think is a shame.
Again. .thanks ya"ll.
Michael(astronomy fm) Pluto is an average of 40 AU's away but because of it's eccentric orbit doesn't it get as far as 90 AU's out?? I can not wait to hear about all the data we get from New Horizons (going to pluto- will report in 2015).
I also hold the Voyager spacecraft in very high regard. They are simply amazing. After reading your comment Michael I am wishing NASA would build a communications array in the solar system.
Just Navarre, I can tell you are a space enthusiast and I know it's easy to get discouraged by the politics involved in our space program but I take exception to those who misrepresent the current state of the space program. If I didn't know anything about our space program and took you at your word I'd have an utterly wrong picture of the actual state of our space program. You say the "government does not seem interested in a space program anymore". Well, that would indeed be a shame but it's not at all the case. The U.S. government is investing billions of dollars a year in space exploration. This number has and will continue to grow. It's true that the shuttle program is being retired and I find this a very sad time indeed. But the program is being replaced with another system that the politicians are hoping will save taxpayer dollars (whether or not that will actually happen is anyone's guess) and facilitate manned space flight beyond Low Earth Orbit (LEO).
Some people aren't space aficionados and I feel those of us that truly care about issues of space need to do our best to inform people with accurate information. I don't think it's accurate to say the government doesn't seem interested in the space program. To me the government seems VERY interested in the space program. I would love to see the government put more money and resources behind the space program because it creates good, high-paying jobs here in America, it bolsters pride in America, the space program develops new technologies that help American households daily, and the list just goes on and on! Investing in the space program makes America money. There are those who can not imagine why America spends money on NASA but they just haven't looked close enough to see that there is a TREMENDOUS return on our (taxpayers) investment in the space program.
Hiya Mob!
Pluto's orbit varies from 30 to just shy of 50 AU's from the Sun.
I also am waiting oh so patiently for New Horizons to get our first gooder look at Pluto, and its moons (Charon, Nix, and Hydra).
Better yet - if all goes well it's hoped that the New Horizons probe will be re-targeted to another plutoid after visiting Pluto.
~Michael
hmm, I wonder where the heck I got the 90 AU number from. Oh well, I always appreciate being corrected when I'm wrong. Thank you Michael! The geology of Pluto should be very interesting as well as it's moons. I would love to see more information about Neptune and Uranus. I have a dvd called Journey (put out by national geographic) and it talks about all the planets (narrated by Alec Baldwin- hilarious) but they only talk about Uranus and Neptune for about 5 minutes altogether. Anywho, I'm a big fan of the comments you post as they are always brimming with great info. Keep up the good work.
Sedna (another Kuiper Belt Object; it's a pretty healthy percentage of the size of the PLANET Pluto) is about 90 AU's out - so perhaps you picked it up there.
VOYAGER PROGRAM on ASTRONOMY.FM RADIO (AFM*Radio):
After all this talk about Voyager, one of my favorite space program accomplishments, I've selected an episode of "The Groks Science Radio Show" about Voyager to run tonight and tomorrow.
The program airs on AFM*Radio (an internet radio station; the broadcast service of Astronomy.FM). It's will air on Thursday at 12:15am, 4:15am, 8:15am, 12:15pm, 4:15pm, and 8:15pm (all times approximate - U.S. Eastern time).
The program will be preempted for live coverage of the launch of the Shuttle Discovery, and (it's a DOUBLE-FEATURE!) the expected NASA briefing for Deep Impact's flyby of Comet Hartley 2.
Thursday is gonna be a great day to explore space!
GO DISCOVERY! GO DEEP IMPACT!
~Michael (AFM*Radio / Astronomy.FM)
From an engineering standpoint all systems have harmonics related to applied force and the moment of inertia of the system. I think the fun part of it will be figuring out what force is causing the phenomenon and what other forces are influencing it. Gravitational? Electrostatic? Radiation? Solar wind? Coriolis? Maybe a blend of all.
Thank you so much for your opinion. You are entitled to it as much as I am entitled to mine. . .
My last post was to mob_barley.
I think we both want the same thing here so just so I'm clear on it could you describe what it would take for you think it "seemed" like the government was interested in the space program? What would you like to see happen for the space program? I'm actually interested JN so I hope you respond.
mob_barley
It is Just Navarre. . .not JN.
Have a nice day.
wow, I didn't mean to offend you your majesty, oops sorry Just Navarre. I ask your opinion on something and that's how you respond?