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(meteorobs) Excerpts from "CCNet 129/2000 - 8 December 2000"
Two interesting meteor-related items in this issue... Also, in the related
"CCNet CLIMATE CHANGE" Digest, I noted this fascinating quote from Greening
Earth Society Science Advisor Robert C. Balling Jr., regarding the decline
in intraday temperature variations across the globe: "Variations in diurnal
temperature range even have been related to phases of the moon!"
Of course, amateurs ALWAYS knew that the Full Moon causes clear skies... ;>
Anyway, note the fine article about the New Hampshire "meteorite" below.
Lew Gramer
------- Forwarded Message
From: Peiser Benny <B.J.Peiser@livjm.acdot uk>
To: cambridge-conference <cambridge-conference@livjm.acdot uk>
Subject: CCNet, 8 December 2000
Date: Fri, 8 Dec 2000 10:31:52 -0000
CCNet 129/2000 - 8 December 2000
--------------------------------
[...]
(5) STARDUST AND CARBON IN THE UNIVERSE
ScienceWeek, 1 December 2000
(6) FIRE FROM THE SKY
Bad Astronomer <badastro@badastronomy.com>
[...]
===============================================================
(5) STARDUST AND CARBON IN THE UNIVERSE
>From ScienceWeek, 1 December 2000
http://scienceweek.com/current.txt
ASTROPHYSICS: ON STARDUST
In astrophysics, the term "dust" refers to various entities: a) interplanetary
and cometary dust are found in the Solar System; b) circumstellar dust is found
around stars; c) interstellar dust is found between stars. Individual dust
particles are usually called "dust grains" and range in size from approximately
10 nanometers up to the micron range (with an average size about the size of
particles in cigarette smoke). Interstellar dust extinguishes and reddens
starlight, can be detected by its absorption and emission of infrared radiation,
and can be detected by its polarizing effect on starlight. The exact composition
of interstellar dust is uncertain, but infrared absorption measurements indicate
that a significant fraction of the material is organic. In general, interstellar
dust is believed to be carbon, iron, and silicates mixed with or coated with
frozen water.
* J. Mayo Greenberg (University of Leiden, NL) presents a review of recent
research on interstellar dust and cometary dust, the author making the
following points:
1) The extinction curve for interstellar dust, which indicates the reduction
of light intensity at each wavelength, indicates there must be 3 types of
dust grains:
a) The particles that block light in the visible spectrum are elongated
grains nearly 0.2 microns in diameter and approximately 0.4 microns in
length. These particles account for approximately 80 percent of interstellar
dust, with each grain containing a rocky core surrounded by a mantle of
organic materials and ice.
b) A hump in the ultraviolet part of the extinction curve suggests the
presence of smaller particles of approximately 5 nanometers diameter,
which comprise approximately 10 percent of the total dust mass. These
grains are most likely amorphous carbonaceous solids that probably contain
some hydrogen but little or no nitrogen or oxygen.
c) Finally, an even smaller type of particle, approximately 2 nanometers in
diameter, is apparently responsible for blocking light in the far ultraviolet
region. These smallest particles, which constitute the remaining 10 percent of
the dust mass, are believed to be large molecules similar to the polycyclic
aromatic hydrocarbons emitted in automobile exhaust.
2) The author postulates a 100-million-year "dust cycle", which dust
grains undergo approximately 50 times before their destruction:
a) In diffuse dust clouds, where gas is sparse, the dust is a mixture of
core-mantle grains, carbonaceous particles, and polycyclic aromatic
hydrocarbon-like (PAH-like) molecules.
b) When the dust enters a dense gas cloud, atoms and molecules of gas adhere
to the core-mantle grains and form an outer mantle of ice. The carbonaceous
particles and PAH-like molecules also accrete on the core-mantle grains.
c) Ultraviolet radiation affects the material in the ice mantle, creating
a layer of complex organic compounds of yellowish color.
d) As the cloud of dust and gas contracts to form a star, some of the
core-mantle dust grains clump together and become comet nuclei. But the
vast majority of the dust is dispersed.
e) Returning to a diffuse cloud, the core-mantle grain is exposed to
harsher radiation that evaporates the ice mantle and further processes
the organic material. The complex of organic compounds turns from
yellowish to brown.
f) Supernova shock fronts accelerate the dust grains, causing violent
collisions that shatter the organic mantles. The debris becomes the
carbonaceous particles and PAH-like molecules.
3) The author points out that as astronomers make new discoveries about
the chemical composition of both comets and interstellar dust, they are
becoming convinced that comets originally formed as clumps of dust grains.
In addition, comet dust may have played a role in seeding life on Earth.
Each loose cluster of comet dust not only contains organic materials, but
also has a structure that is ideal for chemical evolution once it is
immersed in water. Experiments have indicated that small molecules could
easily penetrate such clumps from the outside, while large molecules would
remain sequestered in the interior. The author states: "Such a structure
could stimulate the production of ever larger and more complex molecules,
possibly serving as a tiny incubator for the first primitive life forms.
A single comet could have deposited up to 10^(25) of these 'seeds' on the
young Earth."
-----------
J. Mayo Greenberg: The secrets of stardust. (Scientific American
December 2000)
QY: J. Mayo Greenberg, University of Leiden, NL
-------------------
Summary by SCIENCE-WEEK http://scienceweek.com 1Dec00
For more information: http://scienceweek.com/swfr.htm
-------------------
Related Background:
ON CARBON IN THE UNIVERSE
Carbon is a major factor in the evolutionary scheme of the Universe because
of its abundance and its ability to form complex chemical entities. It is
apparently also a key element in the evolution of prebiotic molecules. The
different forms of cosmic carbon range from carbon atoms and carbon-bearing
molecules to complex solid-state carbonaceous structures, and evidence
gathered during the past decade has considerably enhanced our understanding
of the physical and chemical properties of carbon materials in space.
*Th. Henning and F. Salama (2 installations, DE US) present a detailed
review of the subject, the authors making the following points:
1) More than 75 percent of the 118 *interstellar and circumstellar molecules
identified to date are carbon-bearing molecules, and one component of
interstellar dust is evidently carbonaceous. The cosmic evolution of carbon
from the interstellar medium into *protoplanetary disks and *planetesimals,
and finally into habitable bodies, is intrinsic to the study of the origin
of life.
2) Carbon plays an important role in the physical evolution of the
interstellar medium because it is the main supplier of free electrons
in diffuse interstellar clouds, thus contributing to the heating of
interstellar gas.
3) The observation of unidentified ubiquitous molecular and solid-state
features in astronomical spectra, and the realization that these features
are linked to carbonaceous materials, have resulted in major scientific
progress in the past decade. Laboratory and theoretical studies stimulated
by these astronomical observations have led to a better understanding of
the various forms of cosmic carbon such as polycyclic aromatic hydrocarbons,
carbon-chain molecules, carbon custers, and carbonaceous solids. These
investigations have also led to the detection of novel forms of carbon and
laid the foundations for the chemistry of *fullerenes.
4) The authors present the following categorization of carbon in space:
a) Carbon-rich circumstellar envelopes around *red giant and *asymptotic
giant branch (AGB) stars: CO, C(sub2)H(sub2), complex hydrocarbons,
gas-phase polycyclic aromatic hydrocarbons.
b) Diffuse interstellar medium: C+, simple diatomic molecules, gas-phase
polycyclic aromatic hydrocarbons and carbon chains.
c) Dense interstellar medium: CO, complex hydrocarbons.
d) Interstellar material in primitive meteorites: polycyclic aromatic
hydrocarbons.
5) The authors suggest that the widespread distribution of complex
organics in the interstellar medium has profound implications for
our understanding of:
a) the chemical complexity of the interstellar medium,=20
b) the evolution of prebiotic molecules,=20
c) the impact of this evolution on the origin and evolution of life on
early Earth through the exogenous delivery (by cometary encounters and
meteoritic bombardments) of prebiotic organics.
-----------
Th. Henning and F. Salama: Carbon in the Universe.
(Science 18 Dec 98 282:2204)
QY: Th. Henning, Astrophysikalisches Institut und
Universitats-Sternwarte, Schillergabchen 2-3, D-07745, Jena DE.
-----------
Text Notes:
* interstellar and circumstellar molecules: In this context, an
interstellar molecule is any molecule that occurs naturally in clouds
of gas and dust in space. In general, a circumstellar molecule is any
molecule that occurs in gas and dust surrounding a star.
* protoplanetary disks: These are dust disks surrounding young stars;
it is from these disks that planets presumably form.
* planetesimals: Planetesimals are bodies with dimensions of 10^(-3)
to 10^(3) meters that are believed to form planets by a process of
accretion. The term "accretion" refers to an aggregation, an increase
in the mass of a body by the addition of smaller bodies that collide
and adhere to it, provided the relative velocities are low enough for
coalescence. As the mass of the agglomerate increases, so does the rate
of accretion, and this accretion process is believed to generally occur
in the form of a disk. A stellar accretion disk is a swarm of dust
grains that evolve into planetesimals and then planets.
* fullerenes: Fullerenes are large molecules composed entirely of
carbon, with the chemical formula C(sub n), where n is any even number
from 32 to over 100. They apparently have the structure of a hollow
spheroidal cage with a surface network of carbon atoms connected in
hexagonal and pentagonal rings.
* red giant: A red giant star is a star in a late stage of evolution.
Having exhausted the hydrogen fuel in its core, the star is burning
elements heavier than hydrogen. It has a surface temperature of less
than 4700 degrees Kelvin and a diameter 10 to 100 times that of the Sun.
* asymptotic giant branch (AGB) stars: These are stars that occupy a
strip in the *Hertzsprung-Russell diagram that is almost parallel to
and just above what is called the "giant branch" off the
* Main Sequence. Stars evolve from the horizontal H-R branch to the
asymptotic giant branch when they have exhausted the helium in their
cores and are instead burning helium in a shell.
* Hertzsprung-Russell diagram: The Hertzsprung-Russell diagram is a plot
of stellar absolute magnitude against spectral type, and is perhaps the
most useful diagrammatic aid in astrophysics. It allows the portrayal of
the evolution of a star as occurring along various paths in the diagram.
*Main Sequence: The Main Sequence is a region on the Hertzsprung-Russell
diagram where most stars lie, including our own Sun. The evolution of a
star can be diagrammed as a movement along the Main Sequence and an
eventual branching off the Main Sequence to regions associated with
various types of old stars.
-------------------
Summary & Notes by SCIENCE-WEEK http://scienceweek.com 26Feb99
For more information: http://scienceweek.com/swfr.htm
Copyright 2000, Science Week
===============================================================
* LETTERS TO THE MODERATOR *
===============================================================
(6) FIRE FROM THE SKY
>From the Bad Astronomer <badastro@badastronomy.com>
Benny--
The article about a New Hampshire fire possibly sparked by a meteorite =
in
the December 6 CCNet caught my attention. As most of your readers
undoubtedly know, meteorites (at least, ones under a hundred meters in
diameter!) are generally cool when they hit, and will not spark a fire. =
The
story had enough merit, however, for me to follow it up. I talked to
Stephanie Hanes, the Concord Monitor staff reporter who wrote the =
original
story, as well as Sandt Michener, who works at the Christa McAuliffe
Planetarium in Concord. They directed me to some of the witnesses.
Dick Szopa, a local resident of Salisbury, New Hampshire, was probably =
the
first person to see it. I talked with him about what he saw. Some of =
his
description was consistent with a meteor, but some was decidedly not. =
The
object was falling from the sky when he first saw it, but he stated =
several
times that it "arched" across, and went so far as to compare it to a
basketball thrown at a hoop. That alone would indicate it was not a =
meteor,
which would have been falling straight in.=20
There were two fires, separated by a couple of meters. There is no
indication of any remaining object that might have started the fires. =
If it
had been a meteor, it would either have had to split into two pieces or
bounce, both of which strike me as highly unlikely given the lack of a
"remnant".=20
The owner of the property on which the object hit is David Ayoub. He =
said a
pass with a metal detector gave a positive reading the night of the =
impact,
but the next day around noon there was no reading at the same spot. He
admitted he had not used the detector for some time, but did test it on =
some
coins and it worked properly (even identifying which coin was which). =
There
were a lot of people there (media and the like) between the two times =
he
used the detector, so it's possible that someone found an object and =
took
it.=20
Szopa said that there was no noise despite his being only 200 yards =
away,
and it was moving quickly. Yet there is no crater, and the only holes =
in the
ground look to be from burrowing animals, according to people that were =
at
the scene.
All the accounts are more consistent with something that was thrown =
from a
short distance away. Several of the witnesses said it looked like a =
firework
of some kind, but it was falling quickly with no sound. The location is
fairly rural, with a few houses on 3 acre lots abutting a large deep =
forest.
It's possible that some people were in the woods and launched some sort =
of
fireball
(a Roman candle or some such thing). That would explain the arcing
trajectory, two fires with no remnant and the lack of noise and crater.
Eyewitnesses also describe it as being red, more consistent with =
fireworks
than a meteor.
There are some unconfirmed accounts of witnesses 40 miles away spotting
something in the sky at about the same time, but I have not =
substantiated
these yet. I will not dismiss them out of hand, but it seems this is =
more
likely coincidence given the other accounts.
In my opinion, this is still worth following up, but most likely will =
end up
being something more mundane than a meteorite.=20
Followup articles can be found at
http://www.concordmonitor.com/stories/front0400/salisbury_fireball.shtml=
(which mentions CCNet and a few familiar names!) as well as
http://www.msnbc.com/local/mul/m2678.asp
- -Phil Plait
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