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View Full Version : Comet Collisions Could Cause Rippled Planet Rings



Sev
04-04-2011, 06:16 AM
http://www.spaceref.com/news/viewpr.html?pid=33161

<span style="color: #000000">A curious corrugated pattern in Saturn's rings and similar features in Jupiter's main ring could be the residual effects of comet collisions, report astronomers at Cornell and the SETI Institute.

The research, based on images taken by NASA's Cassini, Galileo and New Horizons spacecraft, underscores the rings' valuable role in chronicling solar system history, the astronomers say. They describe the research in two papers released electronically by Science March 31.

Cassini scientists first noticed spiral ripples in a 2,000 km-wide (about 1,200 miles) swath of Saturn's D ring (the ring closest to the planet) in 2005, said Matt Hedman, Cornell research associate and lead author on one of the papers. In 2009, when the ring plane swept through the sun's position, the astronomers recognized more extensive corrugations covering the entire 17,000 km-wide (10,600 miles) C ring and began looking for clues about their origin.

By comparing the 2005 and 2009 data, Hedman, co-author Joseph A. Burns, Cornell professor of astronomy and the Irving Porter Church Professor of Engineering, and colleagues were able to chart how the ripples changed over time and space.

They found that the spiral formation was getting tighter as it "wound up" around the planet, like a piece of cloth being twisted around a central point. They then worked backward to "unwind" the spiral back to a flat sheet whose orbit was tilted relative to its normal path around Saturn's equatorial plane.

"You could explain this corrugation as if the entire ring had become tilted at some time in the past," Hedman said. That time, according to the calculations, was the fall of 1983.

No one knows what happened in 1983 to cause such a tilt. But as Hedman and colleagues worked on the Cassini data, former Cornell graduate student Mark Showalter, Ph.D. '85, now a scientist at SETI and lead author of the second paper with Hedman and Burns, was examining similar corrugations in the main ring around Jupiter.

Applying the same model, calculations indicated that Jupiter's ring plane was originally tilted in the summer of 1994 -- exactly when the comet Shoemaker-Levy 9 crashed into the planet. This suggested that cometary impacts could tilt rings.

A single solid object, however, would not be enough to knock the rings into a tilted orbit; it would simply plow through the rings and into the planet. But if the object -- an average-size comet, for example -- had been pulled apart into a diffuse cloud of particles, then the story was different: In that case, the smallest particles could rain down on a broader region and knock the ring out of whack.

And the evidence these collisions leave behind in the rings can offer clues about the formation and evolution of the solar system as a whole, Burns said.

"We're realizing that the outer solar system is a much more dynamic place than we had previously believed, and that the rings can actually be witness plates to events in the distant past," he said. "And that gives us an opportunity to say how many objects are out there ... and also to learn a little bit more about how planetary rings evolved."

# # #

The Cassini mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology, manages the mission for NASA's Science Mission Director
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LWW
04-04-2011, 06:37 AM
That makes good sense.

If you have access to even a small scope, a solid tripod support being more important than sheer front lens size, Jupiter is an astounding thing to behold.

Sev
04-04-2011, 06:50 AM
I always enjoy looking at NASA's photos of it. I used to be quite an astronomy enthusiast.

I would still like to get a reflecting telescope with a 10 or 12" barrel.

LWW
04-04-2011, 07:01 AM
A Dobsonian is the most cost effective means to achieve that.

I've actually kicked the idea of THIS (http://www.meade.com/product_pages/lightbridge/lightbridge_10/lightbridge_10.php) around, at $599 it's a ton of bang for the buck ... but totally manual.
THIS (http://www.meade.com/product_pages/etx_series/etx_90/etx_90.php) is a newer model of ours, not near the light gathering ... but compact and the "GOTO" feature is the shizzle.

Sev
04-04-2011, 07:09 AM
The Mead looks like a pretty sweet unit.
I used to be pretty good at dialing in. However constantly adjusting would get a bit tedious.

I have looked at the ETX style units for years.

LWW
04-04-2011, 07:20 AM
Celestron also makes good stuff.

I bought ours about 10 years ago and they have become less expensive over time.

Soflasnapper
04-04-2011, 10:15 AM
Fascinating, and amazing that we're around to have seen when the Jupiter rings got perturbed by that comet or comets (was it all in one piece prior to Jupiter's gravity tearing it up, or was it always in pieces? If always in pieces, was it A comet or rather cometS?).

The ancients considered the heavens unchangeable, and for us to notice some dramatic changes (and the red spot is changing also) is quite good generational luck.

I've always lusted after the Celestron myself.

LWW
04-04-2011, 12:58 PM
For all practical purposes Jupiter is unchanged, although it being struck by cosmic debris is not only common place ... it is probably the main reason that a species survived long enough to develop civilization.

Jupiter has taken nearly all the heavy blows as it's gravitational pull catches nearly all the bad stuff ... with the Moon acting as a secondary line of defense for us.

Soflasnapper
04-04-2011, 08:38 PM
Yes, that's true. But it's amazing that however huge planet can take a hit from something that was about as large an extant as the planet Earth and just shrug its shoulders and say, 'did you feel something?' and keep on keeping on.

A big sucker, dwarfing even Saturn.

Sev
04-04-2011, 09:03 PM
Now that was funny. /forums/images/%%GRAEMLIN_URL%%/smile.gif

Well its good to know a few of enjoy the sciences.
I used to post more of the like, however it generally got stifled by all our political threads.

LWW
04-05-2011, 03:43 AM
Jupiter is huge, but again ... that's why it gets hit so often.

Smaller planets/moons have less gravitational pull and are must smaller targets physically.

Going from memory, Jupiter is something like 1,200 times the volume and 300 times the mass of the planet Oit.

LWW
04-05-2011, 03:44 AM
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Sev</div><div class="ubbcode-body">Now that was funny. /forums/images/%%GRAEMLIN_URL%%/smile.gif

Well its good to know a few of enjoy the sciences.
I used to post more of the like, however it generally got stifled by all our political threads. </div></div>

Science rocks, and I'm quite impressed that this hasn't been trolled yet.

Sev
04-05-2011, 06:47 AM
Hey Larry you wouldnt be a rockhound perchance??

LWW
04-05-2011, 07:49 AM
As in meteor chaser?

Sev
04-05-2011, 08:18 AM
Guess your not.
Geology rockhound.

LWW
04-05-2011, 09:00 AM
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Soflasnapper</div><div class="ubbcode-body">I've always lusted after the Celestron myself.

</div></div>

I also have a pair of Celestron 20 X 80 binoculars that are great for lunar or nebular or planetary viewing.

The ETX was bought because I was an earlier adopter of "GOTO" tech and they were the first to have it in a reasonably priced and compact size.

Someday I will break down and buy an 8 inch SCT from one or the other major makers.

LWW
04-05-2011, 09:01 AM
I've thrown some rocks at neighborhood hounds.

LWW
04-05-2011, 09:24 AM
Let me add also, for anyone considering a first time scope, most any will do a good job if properly set up.

Here are things to be concerned with:

- f rating. This number is the same thing as f stops on a camera lens, other than it is not adjustable. Many beginners get confused over f numbers, or focal ratios ... but it's really simple once you know what it is. the "f" number is the focal length ... or length of the optical tube ... divided by the distance across the front lens glass.

- IOW ... a 400mm optical tube with a 40mm front lens glass will yield an f number of f10:1 ... commonly referred to as f10.

- Similarly, a 200mm tube with the same front element would yield an f5 rating. In the "BIGGER IS BETTER" mentality, most people will assume the longer tube is "better" ... which depends on your definition of better.

- A smaller f number means that you will get a much brighter view of whatever you view, and will be able to see details that you might miss with a darker, higher f number.

- A longer tube will allow for larger, albeit darker, magnifications.

- Ignore scopes that offer "HUGE" powers of magnifications as it is marketing snake oil.

- With premium stuff and ideal viewing condition ... dark sky, isolation, constant temperature ... you might get a usable ... meaning non jittery ... magnification of 400 power. Maybe.

- A reasonable maximum magnification under normal atmospheric conditions is 250 power with good stuff.

- Most observing will be done between 25 and 100 power for most people.

- A $100 fifty power spotting scope on a stout tripod will be more enjoyable to use than a $2,000 scope on a flimsy tripod. The reason is simple, a scope is simply a light lever ... IOW if you are watching something at 50 power and the scope shakes 1/1,000 of an inch, the viewed object will jitter a tenth of an inch and become un-viewable to any degree of serious enjoyment. Cheap department store scopes actually perform quite well if they have the right thread to be attached to a decent camera tripod.

- Learn the sky with a pair of binoculars first. It will not only tell you if you have a true interest, or a fleeting fetish. It will also teach you where things are.

- Invest in a few decent astronomy books or a class. Most people get frustrated because they can't find anything.

Sev
04-05-2011, 11:35 AM
Good advice Larry.

I was always surprised that tripods are preferred rather and a more stable base and attachment system.

A skeltonized aluminum plate base that could be leveled would be far more stable.

LWW
04-05-2011, 05:05 PM
Sorry, but no it wouldn't.

I can tell you that the best thing I ever bought was a set of rubber isolation pads to go under the tripod feet.

Even my spiked tripod which would de facto become one with the ground picks up vibration.

Remember, at 25o times magnification, a vibration that causes .00004 inches of jitter will cause a .1 inch jitter through the viewing lens ... and that is sufficient to be quite noticeable on lunar viewing, and make stars seem to bounce about too much for photography.

Even with the 20 power binocs I use a tripod.

LWW
04-05-2011, 05:09 PM
BTW, if you want to see an example ... point your index finger straight forward and focus your eyes on the tip of your finger while holding your breath.

Then breath normally and watch your finger wobble about.

Now, pool related, have you ever tried taking a breath just before you shoot and not breathe until you have struck the ball? Your bridge is simply a living tripod.

That split second can make a difference.

The same applies to target shooting, take a breath and hold it a second bfore you pull the trigger.

wolfdancer
04-05-2011, 07:38 PM
Well, as they say......there goes the neighborhood
(it's a rather large neighborhood, but...)

LWW
04-06-2011, 01:56 AM
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Sev</div><div class="ubbcode-body">Good advice Larry.

I was always surprised that tripods are preferred rather and a more stable base and attachment system.

A skeltonized aluminum plate base that could be leveled would be far more stable. </div></div>

Upon reading that again, are you talking about a pier type of base?

If so, yes it could offer some added stability but at the cost o mobility.

Sev
04-06-2011, 07:25 AM
Indeed I am. However it would be mobile. The shape of broadhead 4 blade arrow. the base diameter would be determined by the barrel length. However the mounting area would be crucial for stability. Another skeletonized frame attached to a solid platform which in itself would be heavy duty.

LWW
04-06-2011, 07:33 AM
Can you post a pic of something like what you are referring to?

Telescope piers are usually simply poles set in concrete with an elbow made to polar align at the location of use.

LWW
04-06-2011, 07:36 AM
http://www.meade.com/product_pages/lx200_series/images/lx200_16.jpg

16 inch Meade on a pier.

Sev
04-06-2011, 12:26 PM
Its just a design I have in my head. It could also be in the configuration of a 3 blade broadhead arrow. The key would be to both have feet on it that completely stabilize the structure and have a heavy duty mounting apparatus for the scope. perhaps similar to the knuckle on the Meade.

Also the base could break down for portability. However it would require good locking mechanisms that would assure that there would be no movement between the pieces.
No less than half inch aluminum plate as you dont want any chance of harmonic vibrations caused by wind passing through the frame work.

Sev
04-06-2011, 12:27 PM
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: LWW</div><div class="ubbcode-body"> http://www.meade.com/product_pages/lx200_series/images/lx200_16.jpg

16 inch Meade on a pier. </div></div>

Man thats got to be pricey.
Very sweet though.