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Planetary Ring Around Earth - Part 1 of 3
Lou Varricchio schrieb:
> Subject: Saturn-Like Ring Around the Earth
>
> The April 1999 issue of DISCOVER science magazine, p. 20, has a
> story about two U.S. scientists proposing that a ring of ejecta by
> the so-called K-T impactor created a temporary ring around the
> Earth whose shadow had a profound affect on climate change at
> the end of the Cretaceous.
Hello Lou and List!
I thought this might be of interest to you:
Meteoritics 27-3, 1992, p. 292:
A planetary ring around Earth as source for the Ir-enrichment at the
K/T-boundary (M. Stage and K.L. Rasmussen)
Department of Physics, University of Odense, Campusvej 55, DK-5230
Odense M, Denmark
Since the discovery of the Ir-enrichment at the Cretaceous-Tertiary
boundary a majority of the researchers have claimed a meteorite impact
as origin of the event, but the search for an impact crater has not been
conclusive. Alternative explanations have been suggested, e.g., a
volcanic origin (Hansen, 1990). If, however, we maintain that the
KT-boundary material is extraterrestrial, the missing crater constitutes
a problem.
The missing-crater-problem can be solved by postulating the existence of
a temporary planetary ring around the Earth. We suggest the following
scenario: an incoming asteroid is captured by the Earth inside the Roche
limit, and the breakup of the asteroid creates a planetary ring.
Atmospheric drag and partially inelastic collisions between particles
cause the ring particles to lose energy and slowly accrete onto Earth.
Once the asteroid is decomposed, the atmospheric drag on the ring
particles will primarily drain the smaller particles from the ring (Fig.
1). The figure shows residence times as a function of starting position.
Each curve represents one particle size. Thus the needed amount of Ir is
brought down to Earth as a gentle rain lasting perhaps thousands of
years, without major crater production.
Our 3D computer simulations of the ring dynamics show accretion
profiles, which are comparable to the Ir profiles at the KT-Boundary. In
our model partially inelastic collisions occur between ring particles
(Brahic, 1976; 1977) and the particles experience a slight atmospheric
drag (10^-14 atm at 0.75 Earth radii). The particles are injected into
randomly oriented orbits near the Earth upper atmosphere, from 0.1 to
0.75 Earth radii. The number and the density profile of the inward
spiralling particles are calculated, until the distance from the Earth
is small enough to assure that they are lost to the Earth surface within
a few hours. The profile reflects the composition of the ring, and
thereby the asteroid.
In conclusion we suggest that a planetary ring formed around the Earth
prior to the KT-boundary event, and that the Ir enrichment at the
KT-Boundary layer is formed by a slow accretion from a planetary ring
rather than from a giant impact. This explains the gradual rise in
Ir-content prior to the peak event at the boundary layer (Hansen et al.,
1988) and the gradual decrease in Ir-content found in the sediments
after the peak event.
References:
Brahic A. (1976) J. of Computational Physics 22, 171-188.
Brahic A. (1977) Astr. and Astrophysics 54, 895-907.
HANSEN H.J., GWOZDZ R. and RASMUSSEN K.L. (1988) Revista Espanola
Paleontologia (extra vol:) 21-29.
HANSEN H.J. (1990) Geological Soc. Am. Spec. Pap. 247, 417-423.
Best regards,
Bernd
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