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Planetary Ring Around Earth - Part 2 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.


Meteoritics 28-3, 1993, pp. 442-443:

Accretion from a planetary ring around Earth as a possible explanation
of the shape of their peak at the K/T Boundary

M. Stage and K.L. Rasmussen. Department of Physics, University of Odense
Campusvej 55, DK-5230 Odense M, Denmark

At most K/T boundary localities the Ir distribution exhibits shoulders,
i.e., a gradual increase in the Ir content of the boundary material
immediately before the K/T event and a gradual decrease in the Ir
content after the K/T event. Here we investigate a version of the impact
hypothesis that accounts both for the central peak and the shoulders of
the Ir distribution.
If the Ir is of extraterrestrial origin, the shoulders of the Ir
distribution can be explained in two ways. The shoulders may reflect
that boundary material has been redistributed by diffusion or
bioturbation. But, as local chemical and biological environments must
have been widely different at various localities, the fact that the
shape of the Ir peak, with shoulders on both sides of the peak, is
ubiquitous makes redistribution by bioturbation [1] or by diffusion [2]
unlikely. Alternatively, the shoulders of the Ir peak can be interpreted
as a primary signal from the accretion of a planetary ring around the
Earth.
The evolution of a planetary ring encompasses two phases, first a fast
and violent phase where all orbital elements change rapidly, and then a
second much longer and more quiet phase. In the second phase of the
development, the ring is in quasi-equilibrium [3]. The ring particles
are thought to be remnants of a decomposed asteroid inside the Roche
limit of the Earth.
Accretion profiles from a temporary ring around the Earth was shown to
have similarities to the Ir concentration at the K/T boundary [4]. We
have now produced accretion profiles by a three-dimensional computer
simulation of the dynamics of the quiet phase of a ring around the
Earth. In the model the ring particles interact with one another in
partly inelastic collisions and with the atmosphere of the Earth through
a drag force. The collisions between the ring particles are too gentle
to cause large-scale fragmentation of the particles.
Figure 1 shows a typical accretion profile from a planetary ring around
the Earth with two particle radii, calculated by our model. We assume
that the asteroid was fully differentiated. The major part of the ring
particles will be small Ir-poor silicate particles and only a minor part
will be larger Ir-rich metallic particles. The main part of the silicate
particles will accrete first, and after several thousand years the
metallic particles will accrete onto the Earth, constituting the central
Ir peak. Finally, the remaining silicate particles will accrete together
with the very few remaining metallic particles, and thereby create the
upper shoulder of the Ir peak.
The variation in magnetic susceptibility of marine and terrestrial
deposits at several K/T boundary localities indicate that the duration
of deposition of the K/T boundary material is ~40 ka [5]. This timescale
is in good agreement with the duration of accretion from a planetary
ring around the Earth.

References:

[1] Dyer B.D. et al. (1989) Geology, 17, 1036-1039.
[2] Tredoux M. et al. (1989) J. Geol., 97, 585-605.
[3] Brahic A. (1976) J. Computational Phys., 22, 171-188.
[4] Stage M. and Rasmussen K.L. (1992) Meteoritics, 27, 292.
[5] Hansen H.J. et al. (1992) Meteoritics, 27, 230.


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