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Posted by: SigurRosFan Apr 6 2006, 11:11 AM

- http://arxiv.org/abs/astro-ph/0604079 - Shoemaker-Levy 9 Impact Modeling: I. High-Resolution 3D Bolides

--- We have run high-resolution, three-dimensional, hydrodynamic simulations of the impact of comet Shoemaker-Levy 9 into the atmosphere of Jupiter. We find that the energy deposition profile is largely similar to the previous two-dimensional calculations of Mac Low and Zahnle (1994), though perhaps somewhat broader in the range of height over which the energy is deposited. As with similar calculations for impacts into the Venusian atmosphere, there is considerable sensitivity in the results to small changes in the initial conditions, indicating dynamical chaos. We calculated the median depth of energy deposition (the height z at which 50% of the bolide's energy has been released) per run. The mean value among runs is approx 70 km below the 1-bar level, for a 1-km diameter impactor of porous ice of density rho=0.6 g cm^{-3}. The standard deviation among these runs is 14 km. We find little evidence of a trend in these results with the resolution of the calculations (up to 57 cells across the impactor radius, or 8.8-m resolution), suggesting that resolutions as low as 16 grid cells across the radius of the bolide may yield good results for this particular quantity. ---

Posted by: ljk4-1 Apr 7 2006, 11:40 PM

Speaking of comets breaking apart (if only we had a well-shielded probe
following this one. Who needs to make a crater with a copper ball when
you've got the whole comet revealing its interior to you):

Space Weather News for April 7, 2006

http://spaceweather.com

Dying comet 73P/Schwassmann-Wachmann 3 continues to break apart. Astronomers are
tracking at least 20 fragments approaching Earth for a harmless but beautiful
close encounter in May.

In particular, fragment B of the comet has brightened 15-fold since April 2nd.
This signals a possible breakup of "73P-B" into even more fragments. Amateur
astronomers with backyard telescopes and CCD cameras can monitor the ongoing
disintegration. Visit Spaceweather.com for sky maps, images more information.

Posted by: ljk4-1 Apr 11 2006, 03:02 PM

Hybrid comet-asteroid in mysterious break-up

09:30 11 April 2006

NewScientist.com news service

Jeff Hecht

Something substantial has broken off an icy 50-kilometre object beyond the orbit of Saturn, leaving puzzled astronomers trying to figure out why.

Comets have been seen breaking up before, but only after heating when passing close to the Sun or a gravitational disturbance following a close encounter with a planet.

However, at 1.9 billion kilometres, this object is very far from the Sun. Another mysterious feature is that much more gas and dust is escaping from the breakaway fragment than from the parent body. The disintegration has created a dust cloud more than 100,000 km across and which is several times brighter than the original object was before the event.

The object, called 60558 Echeclus, was discovered in 2000 and is a “centaur” - part rocky asteroid and part icy comet. Its new activity, revealed in images taken on 2 April, makes it look “really strange", says William Romanishen of the University of Oklahoma, US, one of the team that took the images. "The first thing that came to mind was a collision."

Earlier observations showed Echeclus rotates about once every 26 hours, so a fragment would need a push to escape its gravity, says Paul Weissman of the Jet Propulsion Laboratory, who spotted the original cloud of gas and dust around Echeclus on 30 December 2005.

Full article here:

http://www.newscientistspace.com/article/dn8976-hybrid-cometasteroid-in-mysterious-breakup.html

Posted by: BruceMoomaw Apr 11 2006, 08:29 PM

QUOTE (ljk4-1 @ Apr 7 2006, 11:40 PM)

Posted by: ljk4-1 Apr 17 2006, 06:17 PM

Fragmented Comet Will Sweep By Earth Next Month

http://www.spacedaily.com/reports/Fragmented_Comet_Will_Sweep_By_Earth_Next_Month.html

Boulder CO (SPX) Apr 17, 2006 - Astronomers tracking Comet
73P/Schwassmann-Wachmann 3 report that the near-Earth object continues to break
apart, with at least 20 fragments now approaching the planet for a close
encounter next month.

Posted by: BruceMoomaw Apr 17 2006, 06:37 PM

That article confirms that it did break up very recently -- some time between 1990 and 1995. This makes CONTOUR's failure even more of a pity; it begins to look as though SW3 will crumble completely before any other mission can get a look at a cross-section of one of its fragments.

Posted by: ljk4-1 Apr 19 2006, 02:51 PM

IRON AND ICE

- Fragmenting Comet Flyby To Be Webcast

http://www.spacedaily.com/reports/Fragmenting_Comet_Flyby_To_Be_Webcast.html

New York NY (SPX) Apr 18, 2006 - Slooh.com, an astronomical event Web site, said
Tuesday it will begin live monitoring of the approach of Comet 73P
Schwassmann-Wachmann, beginning this week at 9 p.m. Eastern Time.

Posted by: ljk4-1 Apr 24 2006, 03:22 PM

Thirty pieces and counting, some of which may reach magnitude 4.

I presume there is no way to get any space probes near one of these
chunks? Is the HST scheduled to image any of them?


Space Weather News for April 22, 2006

http://spaceweather.com

COMET NEWS: Astronomers are now monitoring more than 30 fragments of
dying comet 73P/Schwassmann-Wachmann 3, which is approaching Earth for
a close encounter in mid-May. One of the brightest fragments, fragment B,
is splitting in two in plain view of amateur astronomers using backyard
telescopes. Visit Spaceweather.com for pictures of the breakup, sky maps
and more.

Posted by: The Messenger Apr 24 2006, 06:01 PM

Maybe it is time for an ice cream scoop theory: Comets shovel icy particulate picked up in the Kuiper belt into the inner solar system, dumping their load with every visit

Posted by: antoniseb Apr 24 2006, 07:38 PM

Surely you are not saying that comets have any way to accumulate a significant amount of icy material when in the outer part of the Solar System each orbit.

Posted by: The Messenger Apr 25 2006, 05:53 PM

No, but I think that it is interesting that only a couple of chunks of 73P/Schwassmann-Wachmann 3 behave like comets, and every comet we have looked at closely seems to be mostly black stuff. Extrapolating, is it reasonable to assume most 'comets' are invisible and we only see the occasional comet that has a enough moisture content near or on the surface to show its face? Extrapolating even more, this would mean there is a lot more stuff in the Kuiper belt and beyond than imagined. Are the contraints on possible Kuiper belt objects based upon forground or background observations?

Posted by: edstrick Apr 26 2006, 05:04 AM

"Black Stuff"....

Even though exposed comet nucleus material (at least in the inner solar system) is mostly as black as laserjet toner... about 4% reflectivity, it's not 0% reflective. It's *** ENORMOUSLY *** difficult to make anything signigicantly blacker.

If bare comet nucleii had significant amounts of exposed water, like the water-bearing higher albedo exposures on a very limited fraction of Temple-1's surface, but much greater (enough to influence brightness), it would dramatically show up in the near and middle infrared spectrum.

Generally, size/frequency distrubution limits based on brightnesses of observed populations use "best guess" albedo assumptions based on larger members of the population, but not the largest (whicy may be atypical) For comet nucleii, they're plugging in an albedo of around 4%.

Also.. if there really were absolutely black objects, they'd show up perfectly well in the thermal infrared. a 4% and 0% reflectance black surface will heat up to essentially the same temperature, as long as they're not strongly heat absorbing

Posted by: The Messenger Apr 26 2006, 03:00 PM

QUOTE (edstrick @ Apr 25 2006, 11:04 PM)

Posted by: ljk4-1 Apr 27 2006, 06:41 PM

Compare these new images of the Breakup Comet from HST:

http://hubblesite.org/news/2006/18

http://www.jhuapl.edu/newscenter/pressreleases/2006/060427.asp

http://www.spacetelescope.org

With this one from a ground-base amateur astrophotographer via
Spaceweather.com:

http://spaceweather.com/swpod2006/27apr06/hergenrother1.gif

The latter is a bit blurrier, but otherwise pretty darn good, showing
quite a few of the new comet chunks.

Posted by: BruceMoomaw Apr 27 2006, 11:12 PM

ESA has a new sequence of Hubble photos showing the really spectacular fireworks display that SW3 is turning into. It really starts to look as though nothing will be left by the time that a CONTOUR 2 spacecraft could get there.

http://sci.esa.int/science-e/www/area/index.cfm?fareaid=1

Posted by: djellison Apr 27 2006, 11:14 PM

At the BAA Out of London meeting this weekend just gone ( a tie in with the 125th aniv of the Liverpool Astronomy Assoc ) - we had a half hour session on the Faulkes North scope....
http://www.britastro.org/baa/

http://britastro.org/baa/images/stories/news/73p_b_20060422_ftn.jpg

Doug

Posted by: Paolo May 17 2008, 09:30 AM

Anybody knows what is the raw Galileo image of fragment W?
is it the one marked 2844 http://nssdc.gsfc.nasa.gov/planetary/sl9/image/sl9w_gal0600g.gif or the one marked 2890 http://nssdc.gsfc.nasa.gov/planetary/sl9/image/sl9w_gal1000g.gif?

Posted by: tedstryk May 17 2008, 03:03 PM

Those are different transmissions of the raw frame. Here are the four raw transmissions.

Posted by: Paolo May 17 2008, 03:24 PM

Yes, and I remember that the one with the fireball is the first, but I am not sure.