[X] My Assistant

[SigurRosFan]

- 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. ---

[edstrick]

"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