[meteorite-list] Effects of travel through space on comets?

From: Sterling K. Webb <sterling_k_webb_at_meteoritecentral.com>
Date: Sat, 9 Dec 2006 01:04:02 -0600
Message-ID: <018501c71b60$35800060$a925e146_at_ATARIENGINE>

Hi,

    Space is not "empty," E.P. But as for sheer
"drag," the solar system is nowhere near gassy
or dusty enough for drag to be a factor, even in
the very long term (as far as I know).

    Dust and the solar wind is the chief occupant of
the "empty" vacuum here in the solar system, hence
a comet's ionized gas tail always points away from
the Sun because the solar wind is charged particles
mostly. Dust is more influenced by the "pressure"
of light. The smaller the particle, the greater its surface
area for the mass, so smaller particles get a greater
momentum.

    Of course, a debris stream in an eccentric orbit
around the Sun encounters them both at always varying
angles, depending on the eccentricity and where the
particles are in the orbit.

    Debris streams do get sorted by particle size.
Because of the variations, the sorting force is always
shifting. If you had a stream in a circular orbit, the
sort would be more neat and precise, moving the smaller
particles to the "outside" edge of the stream and
leaving the larger pieces at the "inner" edge.

    Then, if the debris particles are rotating, there's
the Yarkovsky Effect. They would rotate, I'm sure,
but it's too late at night for me to explain the
Yarkovsky Effect, so try this:
http://astroprofspage.com/archives/380

    All these sorting effects are responsible for the
density variations in debris streams that make for
spectacular meteor showers or duds. If there are
effects from "dust," it's more likely the effect of
eroding minutely the particles in the stream from
its impact, thus producing more debris.

    The inner solar system, though not dusty enough
for drag, is more dusty than you might think. So
dusty that we can see the Sun's light reflected off
of it: the Zodiacal Light. Comets and asteroids are
the source of the billions (trillions?) of tons of dust
in the Ecliptic Plane.

    The force of light would be enough to disperse
all this dust in less than 50,000 years, by means of
the Poynting-Robertson Effect, and no, I'm too
tired to explain that either, so the dust must be
continually re-supplied to the inner solar system by
the breakup of comets and asteroids.

    IF we knew exactly how much the Zodiacal dust
weighed, we could figure out how much dust is
delivered to the inner solar system per year, century,
millennium, eon... But, the estimates are uncertain and
variable. And, of course, we have no way of knowing
if the Zodiacal dust of today is greater or lesser than
the dust of other eras.

http://adsabs.harvard.edu/abs/1983M&P....28..305M
    "The zodiacal dust cloud's mass loss rate, which
is an important factor in the consideration of its steady
state, has in the past been indirectly estimated on the
basis of the inward mass flux of interplanetary grains
at 1 AU. The rate is presently investigated on the basis
of direct calculations of the orbital behavior of
circumsolar dust grains undergoing sublimation. It
is found that the solar dust ring located at 4 solar
radii from the sun, which consists of grains whose
Poynting-Robertson effect inward spiraling is stopped
by the influence of sublimation, loses its mass at a
rate of 0.35-3.5 tons/sec."

    That high figure works out to 5.5 trillion tons for
the entire mass of the Zodiacal dust; the low figure
to 1/10th of that. That's the delivery of 110,451,600
tons of recent local dust to the inner system per year.

    Since this production of dust would be mostly
from the breakup of comets and asteroids (slow or
fast breakups), that would be a good datum to have
a handle on, if you're concerned about the fate of
small bodies in the inner system.

    Read all about our native dust resources:
http://en.wikipedia.org/wiki/Interplanetary_dust_cloud
    Dust is a hot topic: " Indeed, one of the longest-
standing controversies debated in the interplanetary
dust community revolves around the relative contributions
to the interplanetary dust cloud from asteroid collisions
and cometary activity."

    That 1 hydrogen atom per cubic meter is the
figure for "normal" interstellar space, outside the
solar system. You just can't get a decent vacuum
anywhere these days.


Sterling K. Webb
------------------------------------------------------------
----- Original Message -----
From: "E.P. Grondine" <epgrondine at yahoo.com>
To: <meteorite-list at meteoritecentral.com>
Sent: Friday, December 08, 2006 9:38 PM
Subject: [meteorite-list] Effects of travel through space on comets?


> Hi all -
>
> I was just wondering if any of you have given any
> thought to this -
>
> While we generally think of space as a vacuum, in fact
> it is not. There are "dust" particles (some of them
> chonrdules?), and if I remember correctly, about 1
> molecule of hydrogen per cubic meter -
>
> Now at normal speeds, this would be a vacuum. But
> comets don't travel at "normal" speeds. I am reminded
> of the swimmer who dives from too high a height - the
> water becomes awful hard.
>
> I wonder if drag might change a comet's debris stream,
> putting larger pieces at the head, and smaller pieces
> at the end?
>
>
> good hunting,
> Ed
>
>
Received on Sat 09 Dec 2006 02:04:02 AM PST