From: Mike Lorrey (mlorrey@yahoo.com)
Date: Tue Aug 13 2002 - 18:28:57 MDT
--- Amara Graps <amara@amara.com> wrote:>
> By 'too short', I mean that interplanetary dust spirals into the Sun
> in
> only a few tens of thousands of years. Larger, centimeter-sized
> particles live for tens of millions of years. A similar fate for
> planetary ring ring particles, causing the dust particle to leave
> (inwards or outwards) their particular planet environment on the
> order
> of thousands of years. Radiation pressure forces eject the smallest
> dust
> particles on timescales of one orbital revolution around the Sun.
>
> By 'too long', I mean that afterwards, the dust is already locked up
> in
> meterorites or comets, and so then dust scientists are studying time
> at
> which our solar system formed and earlier.
Well, I was thinking that both the moon and asteroids would be primary
locations to conduct similar strata analysis, since they would
accumulate space dust for many millions of years much as snow
accumulates at Earth's poles. Since the moon is closest and easiest to
work with, I think this would be reason #1 to establish a base on the
moon along the lines of our current Antarctic presence, though I don't
know how much of this sort of record is obscured on the moon by ejecta
sedimentation.
You are right that the current 'flyswatter' technology used on space
probes has it's limitations, though a centimeter sized particle swatter
would be consistent with current ice strata anaylsis in terms of time
scales. Drew has ice core data going back 22 million years now.
>
> Interstellar dust is another situation: it is not bound to our sun
> and has
> a different time history (although still subject to the same forces
> as
> interplanetary dust when it enters the solar system)
>
> But maybe you have heard of Nemesis? I have not heard it mentioned in
> professional circles a while, but I don't think that the idea has
> been killed.
Yes, it's an alleged red or brown dwarf living in the Oort Cloud that
periodically sends showers of comets our way. I can't help, though,
being suspicious about the frequency of earth ELI collisions being so
relatively symmetrical with the frequency of the solar system passing
through galactic arms/the galactic plane (as you point out).
> I heard of two
> astronomical explanations:
>
> 1) The movement of the Solar System through the galactic plane 30 Myr
> period is roughly the same period of time needed for the Solar System
> to oscillate vertically about the galactic plane.
>
> This movement through the galactic plane means that there will be
> collisions or close encounters of the Solar System with clouds of gas
> and dust, which would gravitationally perturb the Solar System's
> "family of comets" (i.e. Oort cloud), and therefore, increase the
> flux
> of comets and meteorites near the earth ("comet showers"), leading to
> large meteoritic impacts.
>
> 2) An invisible solar companion passing through the Oort cloud every
> ~30
> Myr. The perturbation of a solar companion through the Oort cloud was
> speculated to similarly increase the flux of comets and meteorites
> near
> the earth ("comet showers"), leading to large meteoritic impacts.
> This
> latter was the "Nemesis star" or "Death star" idea. (Makes you smile,
> doesn't it?) R.A. Muller and colleagues was the author of this one I
> believe.
>
.....
> Around 1997, R.A. Muller was in the news again, for another "mass
> extinctions" proposal. Muller was proposing, along with another
> scientist named Gordon MacDonald, that interplanetary/interstellar
> dust
> caused the last 10 ice ages. They wrote about it in the October 4,
> 1997
> Science News, and one can follow it in more detail in the July 11,
> 1997
> Science.
>
> Muller and MacDonald said that every 100,000 years for the last one
> million years, there was a period of glaciation. They say that the
> plane
> of the Earth's orbit tilted ("gently") with respect to the orbits of
> the
> other planets every 100,000 years. So at times, the Earth's orbit
> around
> the Sun lined up with the plane of the Solar System, and at those
> other
> times, the Earth's orbital plane was inclined 2.5 degrees. They say
> that
> when the Earth's orbit reaches a certain plane, the planet plows
> through
> an extra-thick cloud of interplanetary dust. ....
This 100,000 year cycle is one of the three Malenkovich cycles (the
other two being the precession of the equinoxes and another orbital
variation relative to distance from the sun).
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