[extropy-chat] Mangled Worlds

[Amara Graps]

>Instead picture grains of dust which slowly float and grind each other
>into smaller pieces, until a big cloud of them smash into an airless
>moon.   Under this picture most of the experience in the small worlds
>is in the floating phase, and only a small part in the smash phase.

Hey.. I like dust analogies! Not very realistic in this universe
though. No magnetic fields or plasmas. I guess your grain size
distribution from the collisions would be about -3, and your dust
cloud would have asymmetries...

Title:
	Impact-generated dust clouds surrounding the Galilean moons
Authors:
	Krueger, Harald; Krivov, Alexander V.; Sremcevic, Miodrag; Gruen,
	Eberhard
Affiliation:
	AA(Max-Planck-Institut fuer Kernphysik, Postfach 103980, 69029,
	Heidelberg, Germany), AB(Nonlinear Dynamics Group, Institute of
	Physics, University of Potsdam, P.O. Box 601553, 14415, Potsdam,
	Germany), AC(Nonlinear Dynamics Group, Institute of Physics,
	University of Potsdam, P.O. Box 601553, 14415, Potsdam, Germany),
	AD(Max-Planck-Institut fuer Kernphysik, Postfach 103980, 69029,
	Heidelberg, Germany)
Journal:
	Icarus, Volume 164, Issue 1, p. 170-187. (Icarus Homepage)
Publication Date:
	07/2003
Origin:
	ELSEVIER
Abstract Copyright:
	(c) 2003 Elsevier (USA)
DOI:
	10.1016/S0019-1035(03)00127-1
Bibliographic Code:
	2003Icar..164..170K
Abstract
Tenuous dust clouds of Jupiter's Galilean moons Io, Europa, Ganymede
and Callisto have been detected with the in-situ dust detector on
board the Galileo spacecraft. The majority of the dust particles have
been sensed at altitudes below five radii of these lunar-sized
satellites. We identify the particles in the dust clouds surrounding
the moons by their impact direction, impact velocity, and mass
distribution. Average particle sizes are between 0.5 and 1 m, just
above the detector threshold, indicating a size distribution with
decreasing numbers towards bigger particles. Our results imply that
the particles have been kicked up by hypervelocity impacts of
micrometeoroids onto the satellites' surfaces. The measured radial
dust density profiles are consistent with predictions by dynamical
modeling for satellite ejecta produced by interplanetary impactors
(Krivov et al., 2003, Planet. Space Sci. 51, 251-269), assuming yield,
mass and velocity distributions of the ejecta from laboratory
measurements. A comparison of all four Galilean moons (data for
Ganymede published earlier; Krueger et al., 2000, Planet. Space Sci.
48, 1457-1471) shows that the dust clouds of the three outer Galilean
moons have very similar properties and are in good agreement with the
model predictions for solid ice-silicate surfaces. The dust density in
the vicinity of Io, however, is more than an order of magnitude lower
than expected from theory. This may be due to a softer, fluffier
surface of Io (volcanic deposits) as compared to the other moons. The
log-log slope of the dust number density in the clouds vs. distance
from the satellite center ranges between /-1.6 and /-2.8.
Appreciable variations of number densities obtained from individual
flybys with varying geometry, especially at Callisto, are found. These
might be indicative of leading-trailing asymmetries of the clouds due
to the motion of the moons with respect to the field of impactors.

----------------------

Title:
	Impact-generated dust clouds around planetary satellites: model
	versus Galileo data
Authors:
	Sremcevic, Miodrag; Krivov, Alexander V.; Krueger, Harald; Spahn,
	Frank
Affiliation:
	AA(AG Nichtlineare Dynamik, Institut fuer Physik, Universitaet
	Potsdam, Am Neuen Palais 10, Bldg. 19, Postfach 601553, D-14415
	Potsdam, Germany), AB(AG Nichtlineare Dynamik, Institut fuer
	Physik, Universitaet Potsdam, Am Neuen Palais 10, Bldg. 19,
	Postfach 601553, D-14415 Potsdam, Germany; On leave from:
	Astronomical Institute, St. Petersburg University, Russia.),
	AC(Max-Planck-Institut fuer Kernphysik, Postfach 103980, 69029
	Heidelberg, Germany), AD(AG Nichtlineare Dynamik, Institut fuer
	Physik, Universitaet Potsdam, Am Neuen Palais 10, Bldg. 19,
	Postfach 601553, D-14415 Potsdam, Germany)
Journal:
	Planetary and Space Science, Volume 53, Issue 6, p. 625-641. (P&SS
	Homepage)
Publication Date:
	05/2005
Origin:
	ELSEVIER
DOI:
	10.1016/j.pss.2004.10.001
Bibliographic Code:
	2005P&SS...53..625S
Abstract
This paper focuses on tenuous dust clouds of Jupiter's Galilean moons
Europa, Ganymede and Callisto. In a companion paper (Sremcevic et al.,
Planet. Space Sci. 51 (2003) 455 471) an analytical model of
impact-generated ejecta dust clouds surrounding planetary satellites
has been developed. The main aim of the model is to predict the
asymmetries in the dust clouds which may arise from the orbital motion
of the parent body through a field of impactors. The Galileo dust
detector data from flybys at Europa, Ganymede and Callisto are
compatible with the model, assuming projectiles to be interplanetary
micrometeoroids. The analysis of the data suggests that two
interplanetary impactor populations are most likely the source of the
measured dust clouds: impactors with isotropically distributed
velocities and micrometeoroids in retrograde orbits. Other impactor
populations, namely those originating in the Jovian system, or
interplanetary projectiles with low orbital eccentricities and
inclinations, or interstellar stream particles, can be ruled out by
the statistical analysis of the data. The data analysis also suggests
that the mean ejecta velocity angle to the normal at the satellite
surface is around 30deg, which is in agreement with laboratory studies
of the hypervelocity impacts.