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(meteorobs) Excerpts from "CCNet, 06/2000 - 18 January 2000"
CCNet, 06/2000 - 18 January 2000
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(12) COSMIC DUST
J.C. Worms et al., ENSPS
(13) YARKOVSKY FORCE ON ASTEROID FRAGMENTS
D. Vokrouhlicky & M. Broz, CHARLES UNIVERSITY
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(12) COSMIC DUST
J.C. Worms*), J.B. Renard, E. Hadamcik, A.C. Levasseur Regourd,
J.F. Gayet: Results of the PROGRA(2) experiment: An experimental study
in microgravity of scattered polarized light by dust particles
with large size parameter. ICARUS, 1999, Vol.142, No.1, pp.281-297
*) ENSPS,EUROPEAN SPACE SCI COMM,PARC INNOVAT,BLVD SEBASTIAN
BRANDT,F-67400 ILLKIRCH GRAFFENS,FRANCE
The PROGRA(2) experiment allows measurements under microgravity
conditions of polarization phase curves for clouds of dust particles.
The sizes that can be used range from a few micrometers to hundreds of
micrometers; regular or irregular particles can be tested. Measurements
obtained on compact particles of boron car bide and silicon carbide are
presented. Results for the silicon carbide, obtained for different
values of the number densities of the particles, indicate that values
of the polarization maximum are lower when measured under microgravity
conditions than on the ground. Although still not fully demonstrated,
this result could be used to understand why it has been difficult to
correlate measurements of the positive branch of the polarization phase
curve done on the ground with actual data on Solar System objects, (C)
1999 Academic Press.
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(13) YARKOVSKY FORCE ON ASTEROID FRAGMENTS
D. Vokrouhlicky*) & M. Broz: An improved model of the seasonal
Yarkovsky force for regolith-covered asteroid fragments. ASTRONOMY AND
ASTROPHYSICS, 1999, Vol.350, No.3, pp.1079-1084
*) CHARLES UNIVERSITY,INST ASTRON,V HOLESOVICKACH 2,CR-18000 PRAGUE
8,CZECH REPUBLIC
We derive a new analytical solution for the seasonal Yarkovsky effect,
the mean-motion frequency mode of the recoil force due to reradiated
sunlight, on a spherical asteroid fragment. The body is assumed to have
a thin low-conductivity (regolith-like) surface layer, covering a much
more thermally conductive core. If the penetration depth of the
seasonal thermal wave in the low-conductivity surface material is
larger than the regolith's geometrical thickness, the previous
simplified solution assuming a homogeneous interior of the body might
lead to wrong estimates on the intensity of the perturbing force. Our
approach removes this problem and the results indicate: (i) an
increased seasonal mobility of 10-m sized and larger fragments with an
insulating surface layer, and (ii) a decreased seasonal mobility of
meter-sized fragments with the same structure. These results may affect
the accuracy of simulations of meteorite and NEA transport to the
Earth, as well as the dynamical evolution of some real small asteroids
(e.g. 1566 Icarus). Copyright 2000, Institute for Scientific
Information Inc.
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