From: Amara Graps (amara@amara.com)
Date: Sun Aug 11 2002 - 07:28:58 MDT
I wrote:
>What I was impressed the most this year at our GUCS meeting was the fine
>level at which we are able to distinguish sources of dust. It used to be
>10-20 years ago, that dust was dust, and we could not say very well from
>where the dust came. Now, from experiments and modeling work, we can
>identify dust from:
>prograde and retrograde, bound and unbound orbits,
>comet Shoemaker Levy 9,
>dust clouds around planetary satellites,
>volcanoes on Io,
>hitting the side walls and main targets of our detectors (!),
>the interior of supernovae,
>AGN stars,
>and more.
Mike Lorrey wrote:
>While tree ring data and ice analysis to date have been used to estimate
>annual climate information, nobody has really tried to use the
>information more discretely to determine where the weather that created
>that local climate came from, outside of a few attempts to correlate
>specific volcanic eruptions with climate changes. Going from using the
>info to create a climate record to creating a weather record thousands
>or even millions of years long is immensely valuable.
>Your work is similar, it seems, though astronomically oriented. Given
>that astronomical phenomena seem to have a huge impact over the long
>term on Earth's climate, I imagine that your work is of similar value to
>the geosciences.
With the exception of the Nemesis idea, I wonder if the dusts' time
scales are too short or too long for dust studies to be of interest to
geophysicists (and depending on where your geophysicists collect the
dust, the natural micrometeoroids must be properly distinguished from
earth debris).
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.
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.
The Nememis proposal, as I understand it, was the following:
Some data by Raup and Sepkoski in 1984 showed major marine extinctions
that looked like it occurred in cycles of about every ~30 Myr. The
cause of the cyclical disturbances (if the fossil record was correct)
was speculated to be astronomical in origin. 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.
Some easy-to-read literature on the topic:
Weissman, P. R., "Are periodic bombardments real?", Sky and Telescope
(ISSN 0037-6604), vol. 79, March 1990, p. 266-270.
Alvarez, L. W., "Mass extinctions caused by large bolide impacts",
Physics Today, vol. 40(7) 24-33, August 1987.
Grasshoff, R., "Comets, "death stars," and extinctions", Astronomy,
vol. 13(3) 18-22, (Jan?) 1985.
The book:
David M. Raup., _The nemesis affair : a story of the death of
dinosaurs and the ways of science_, Norton, 1986
Another book, that is more advanced, seems to have the main arguments
for and against the Nemesis proposal (mostly against, I believe).
Smoluchowski, Roman; Bahcall, John M.; Matthews, Mildred S., _The
Galaxy and the Solar System_, Tucson, AZ, University of Arizona Press,
1986.
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. These particles drift
through the upper atmosphere and set in motion a series of climatic
effects which cool the planet enough to produce an ice age. Later, as
the planet's orbit pulls out of the dust, the climate warms enough to
warm the ice. Their theory was very controversial for many reasons,
and I didn't follow the story afterwards (too busy).
(Aside:
I support the idea of a high school students to write
a report on Nemesis_etal because the story has everything: it is directly
about events in our Solar System; it involves geological records,
interacting galaxies, mass extinctions of organisms, solar system
travels through molecular clouds, influxes of comets, nbody simulations,
stellar evolution, perturbation theory, astronomy history, planetary
evolution, binary stars, celestial mechanics, probability theory...
Also, teachers could use this topic in putting together their courses:
it is a great subject that brings together many different scientific
disciplines in a cohesive way. )
Going back to the topic: I was impressed with dust identified
in all of these:
>prograde and retrograde, bound and unbound orbits,
>comet Shoemaker Levy 9,
>dust clouds around planetary satellites,
>volcanoes on Io,
>hitting the side walls and main targets of our detectors (!),
>the interior of supernovae,
>AGN stars,
because the identification techniques are clever and the measurements
are often direct and clear without compositional analysis (which is
still very rough for in-situ-collected dust). One looks at velocities,
masses, orbit orientations, charges, simply, and those can tell you alot
about the dusts' sources.
Identification of a supernova or AGN by-product is a little more
involved, determined by isotope analysis with special spectroscopic
techniques of meterorites collected from Earth's surface deposits (deep
sea sediments and polar ice) or from dust floating in the stratosphere
(collected with detectors under the wings of high-flying aircraft).
[ Something I wrote related to this: "Dusty Trail from the Solar Nebula
to the Earth" (2000) to help me clarify one possible evolutionary path
of a dust particle from the time of the formation of the solar nebula to
us humans today. Parts of this article were incorporated into my Sky and
Telescope article "Dusty Phenomena in the Solar System", published in
January 2001. http://www.amara.com/ftpstuff/dustytrails.txt ]
You see, once the dust source is identified, those dust particles force
one to think much bigger than ourselves. We are looking at the large
picture, which is really interesting.
Why, 'interesting', you ask? (You did ask, didn't you ...? :-))
Cosmic dust particles evolve cyclically: chemically, physically, and
dynamically. The evolution of dust traces out paths in which the
universe recycles material in processes analogous to the daily recycling
steps with which we are familiar: production, storage, processing,
collection, consumption, and discarding. Observations and measurements
of cosmic dust in different regions provide an insight into the
universe's recycling processes; in the clouds of diffuse interstellar
medium, in molecular clouds, in the circumstellar dust of young stellar
objects, and in planetary systems such as our own solar system. When
scientists study dust, they accumulate observational 'snapshots' of dust
at different stages of its life and, over time, form a more complete
movie of the universe's complicated recycling steps.
The dust evolution cycle follows meandering paths from stardust to
stardust. From the stellar winds of evolved stars, new dust is formed
and is injected into interstellar space. Young stardust is mixed with
old heavily processed diffuse interstellar dust, and is subject to
passing supernova shocks and ultraviolet radiation. Dusty clouds form.
The protostar environment is a fertile ground for solids on all size
scales, from dust grains to planets to form. Star formation in cool
molecular clouds becomes both a sink of old dust and a source of new
dust. A typical dust grain anywhere in space will have undergone several
cycles.
Dust in a planetary system is the most processed (being formed,
destroyed and/or locked into a near-pristine state) of the different
populations of cosmic dust. Interplanetary dust is permanently
replenished by dust ejected from cometary nuclei, the most pristine
bodies in the solar system, and released from collisions in the asteroid
and Kuiper belts. In our solar system, interplanetary dust exists
alongside interstellar dust, which is flowing through the solar system,
offering a tangible physical link between our planetary system and the
stars.
As humans on Earth, we are both the observers of the dust recycling
process, as well as the result.
Amara
-- ************************************************************************ Amara Graps, PhD | Max-Planck-Institut fuer Kernphysik Heidelberg Cosmic Dust Group | Saupfercheckweg 1 +49-6221-516-543 | 69117 Heidelberg, GERMANY Amara.Graps@mpi-hd.mpg.de * http://www.mpi-hd.mpg.de/dustgroup/~graps ************************************************************************ I'M SIGNIFICANT!...screamed the dust speck. -- Calvin
This archive was generated by hypermail 2.1.5 : Sat Nov 02 2002 - 09:16:00 MST