Hi, Larry, Chris, List,
In many ways, this mess is about the "terms
of the trade." It is essential that those working
in a specific specialty understand what each
other mean when they discuss the subject.
The use of "the terms impactors and bolides
for the things that make holes in the ground,"
as Larry called it, makes discussion quick and
effective for those with a "planetary science"
perspective.
Chris' "meteoroid => meteor => meteorite," pretty
much the same as my first definition, is -- yes --
non-IAU-compliant, but from the viewpoint of the
study of meteoritic fall, it is clear and effective
terminology, well understood.
Those who study "meteor showers" use the term
meteoroid as a generic for all the objects contained
within a given "meteoroid stream," even if the object
weighs many tons and is really big enough to be
technically an "asteroid." If it's in a "meteoroid
stream," it must be a meteoroid, right?
In the real world the working vocabulary is, in
practice, determined by those that do common
work, for their own use. But it can't be a "private
language'" That's where the IAU (should) come in.
Opinions may vary on how well they do that job.
The Big Iron that made Meteor Crater is too big to
qualify for "meteoroid." It has to be called an asteroid.
Even the original body of Sikhote-Alin was too big
to be a meteoroid. So we have asteroids that make
meteorites. Even 2008 TC3 was meteoroid by size
but asteroid by designation. The entire classification
system of meteorites has as one major purpose
identifying the parent body in the "Asteroid Zone."
Tracking the origin of "meteoroids" that result in
meteorites has, so far, always traced them back to
Main Belt asteroids.
And while we often don't know the original mass of
most objects that result in found meteorites, most of
the smallish bodies we call meteoroids are too small to
result in meteorites...
It could therefore be more common to get meteorites
from asteroids, and meteoroids may not produce very
many meteorites.
Something about that terminology bothers me.
Sterling K. Webb
----------------------------------------------------------------------------
----- Original Message -----
From: <[email protected]>
To: "Sterling K. Webb" <[email protected]>
Cc: "Meteorite-list" <[email protected]>
Sent: Wednesday, January 13, 2010 6:02 AM
Subject: Re: [meteorite-list] Small Asteroid 2010 AL30 Will Fly Past
TheEarth
Hi all again:
Those who study impacts on Earth and other bodies tend to use the terms
impactors and bolides for the things that make holes in the ground but
too
big leave any meteorite. This gets around the asteroid/comet problem.
I just got this from WIkipedia (same article that Sterling used?:
"Bolide:
The word bolide comes from the Greek âïëéò, (bolis) which can mean a
missile or to flash. The IAU has no official definition of bolide and
generally considers the term synonymous with fireball. The bolide term
is
generally used for fireballs reaching magnitude -14 or brighter.[8] The
term is more often used among geologists than astronomers where it means
a
very large impactor. For example, the USGS uses the term to mean a
generic
large crater-forming projectile "to imply that we do not know the
precise
nature of the impacting body ... whether it is a rocky or metallic
asteroid, or an icy comet,... Astronomers tend to use the term to mean
an
exceptionally bright fireball, particularly one that explodes (sometimes
called a detonating fireball)."
I do not remember in all the emails I read this morning someone asking
about the dark phase. Since the definition of a meteoroid is an object
in
an independent orbit aroung the Sun, once it is in the dark phase, it is
no longer in an independent orbit and is probably going to survive and
so
might as well be called a meteorite. I have always said that the rocky
bit
that causes a meteor is a meteoroid (which we cannot see).
I tell kids that if you can see the thing that is causing the
meteor/fireball---duck!
Now, since I have not had my morning coffee (mentioned this to
Sterling),
the problem with the IAU definition is that it states that a "meteoriod
is
significantly smaller than an asteroid." If that is true, what is
between
a large meteoroid and a small asteroid? A dwarf asteroid (sorry, need my
coffee)!
Now, in support of the IAU and my concern with the proposed Royal
Astronomical Society definition is that we are observing things smaller
than 10 meters and those are given asteroid designations, they are
asteroids. There is no IAU meteroid nomenclature committee!
I think that you need the line between large meteoroid and small
asteroid
to be left "fuzzy." Define a meteoriod as up to 10 meters, but if it is
close enough to the Earth and it gets detected and given a
designaton/name
then it becomes (reclassified as) an asteroid. This makes sense from the
perspective that, when we learn more about something, its designation
can
change (such as large Trans Neptunian Objects becoming dwarf planets as
our knowledge of them increases).
Enough said before my first shot of caffeine.
Larry
Just to make things even more confusing,
the IAU itself has approved the use of the
term "meteor" in a dual sense to include the
physical body itself, thus equating "meteoroid"
with "meteor."
Say what?
Bob Verrish wrote an article about it:
http://meteorite-recovery.tripod.com/2008/mar08.htm
I quote the IAU:
Definition of terms by the IAU Commission 22, 1961.
A. meteor: in particular, the light phenomenon which results
from the entry into the Earth's atmosphere of a solid particle
from space; more generally, as a noun or an adjective, ANY
PHYSICAL OBJECT or phenomenon associated with such
an event.
B. meteoroid: a solid object moving in interplanetary space,
of a size considerably smaller than an asteroid and considerably
larger than an atom or molecule.
C. meteorite: any object defined under B which has reached
the surface of the Earth without being completely vaporized.
D. meteoric: the adjectival form pertaining to definitions A and B.
E. meteoritic: the adjectival form pertaining to definition C.
F. fireball: a bright meteor with luminosity which equals or
exceeds that of the brightest planets.
G. micrometeorite: a very small meteorite or meteoritic particle
with a diameter in general less than a millimeter.
Now, is everything perfectly clear?
I didn't think so...
Sterling K. Webb
---------------------------------------------------------------------------------------------
----- Original Message -----
From: "Jason Utas" <[email protected]>
To: "Meteorite-list" <[email protected]>
Sent: Wednesday, January 13, 2010 12:49 AM
Subject: Re: [meteorite-list] Small Asteroid 2010 AL30 Will Fly Past
TheEarth
Hello Sterling, Larry, All,
Interesting - there's another problem with Sterling's initial
definition, of which the following statement was a component:
"2010 AL30 could be a "meteoroid" if it would hit and
leave a piece to be recovered. Just be very patient and
live a long time... (Always a good idea anyway.)"
As per that definition, though, there's a problem when it comes to
single crater-forming meteorites that don't leave pieces to be
recovered. Yes, they hit the earth, but if they can't be recovered in
any way, can they really be called meteorites (because they don't
technically produce recoverable 'meteorites')?
Admittedly that argument is only a problem if we're using the outdated
version of the definition, but it raises another question.
If an interplanetary object does strike the surface of the earth - and
vaporizes upon impact, is it still considered a meteorite?
Are craters formed by meteorites? Asteroids? I assume a meteoroid
wouldn't be large enough to vaporize itself on impact, but even the
faintest of shooting stars produce dust particles which will
eventually reach the ground.
- So there's a minimum size limit on "meteorites" - they must be
larger than the dust produced by fireballs themselves (apparently),
but as for crater-forming bodies...I've always simply called them
meteorites because, well, in my mind, they've struck the surface of
the earth, so they're meteorites.
Trouble arises if the language of the currently used definition is
specific enough to note that for a meteorite to be a meteorite,
fragments must be recoverable. And if that's the case, then many
craters were in fact formed by...Asteroids? This definition would
also change on individual crater's with time, as older craters might
have arrived with recoverable fragments, but such pieces could have
since been lost to time and weathering (craters generally outlast
meteorite fragments, after all).
So...yeah. A few problems.
Any thoughts?
Regards,
Jason
On Tue, Jan 12, 2010 at 10:04 PM, <[email protected]> wrote:
"My" definition of "meteoroid" is just the standard
textbook definition. Before it hits the Earth, it's
a "meteoroid." While in fiery flight through the
atmosphere, it's a "meteor." If a piece lands on the
Earth (and somebody finds it), it's a "meteorite."<<
I understood that a meteoroid is a small bodied natural object, in a
separate solar orbit from that of earth's. When it enters the earths
atmosphere
and in the incandescent phase, the visible phenomena is a meteor.
Afterwards, during the dark phase, its no longer in a separate solar
orbit from that
of the earth's. It has yet to hit the ground to become a meteorite.
What
is this object called during the dark phase? I personally call it a
meteorite since its under the control of the earth at that point and
not
independent of the earth. Also there has been detected by various
space probes out
around Jupiter, "meteoroids" that are too fast to be in solar orbit
and thus
of interstellar origins. Are these still called meteoroids?
GeoZay
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