[meteorite-list] comet/asteroid classification

From: Rob McCafferty <rob_mccafferty_at_meteoritecentral.com>
Date: Thu, 22 May 2008 16:12:01 -0700 (PDT)
Message-ID: <762262.85936.qm_at_web55210.mail.re4.yahoo.com>

It's a simple case of the terminology being outdated.

The term comet dates back to Aristotle and the name means "star with hair" in Greek. A lovely term that a child could sketch.

The term Asteroid is much more recent (19th Century). The word means "star shaped" probably because that's how they look in a telescope and again, a child looking through a telescope could easily draw it. Going back 200 years, the original distinction is obvious.

Many asteroids have volatiles and many comets probably contain rock elements. I have to say "may" because we haven't studied as many comets as we have asteroid because they tend to be transient and farther away.

I like the child drawing analogy because it demonstrates how our understanding today has matured.

Today we say that, generally, comets come from far out. Generally, asteroids come from much nearer but we all know that the two classes cn overlap in appearance so by the childs analogy, it is possible to confuse the two in individual circumstances. A fresh asteroid from beyond the ice line may take on the appearnce of a comet but a spent comet may take on the appearanc of an asteroid. It does not alter their origin.

It it the terms that are outdated, not the way we classify them.
We saw the same thing in 2006 with planets, a term invented by the Greeks. Planet literally means "wanderer" and when you applied the definitions of the Greeks used, there are only 5 and Earth ain't one of them.

We could change our terminology to accurately classify these bodies according to their origin with sub-classification to describe their current nature. I believe one day we will. It is unlikely to happen anytime soon, however because we do not have the data to categorically state to origin on most of these bodies.

Rob McC




--- On Thu, 5/22/08, Mark Ford <mark.ford at ssl.gb.com> wrote:

> From: Mark Ford <mark.ford at ssl.gb.com>
> Subject: Re: [meteorite-list] Observed lunar meteorite impacts hit 100
> To: Meteorite-list at meteoritecentral.com
> Date: Thursday, May 22, 2008, 5:03 PM
> Yes as I say you can label them, but I still wouldn't
> say the
> differences where 'very distinct'.. juries still
> out on that one. I
> wouldn't mind betting there are quite a few 'icy
> asteroids' out there
> too...
>
> After all:
> > we know little about composition. A burned out comet
> may
> > or may not be similar to an asteroid from a
> mineralogical standpoint.
>
> Given that some moons of Saturn [may] actually be captured
> comets
> (according to the recent Cassini findings), it strikes me
> that we still
> have difficulty in defining exactly what is and isn't
> or what was or was
> not 'a comet', (I guess not enough samples to
> define it clearly enough).
>
> Mark my words - one day we will probably have a 'pluto
> style' mess
> where all those things we classified/call ex-comets etc
> will suddenly
> all be called ... ''rocks''. Lol.
>
> Best
> Mark
>
>
>
>
>
>
> -----Original Message-----
> From: meteorite-list-bounces at meteoritecentral.com
> [mailto:meteorite-list-bounces at meteoritecentral.com] On
> Behalf Of Chris
> Peterson
> Sent: 22 May 2008 15:32
> To: Meteorite-list at meteoritecentral.com
> Subject: Re: [meteorite-list] Observed lunar meteorite
> impacts hit 100
>
> There are clearly two very distinct populations of objects,
> which have
> very different properties. Comets originate in the outer
> edge of the
> Solar System, and ices account for a significant proportion
> of their
> entire mass. Very few ever make it to the inner system, and
> when they
> do, they can usually be identified by their high
> eccentricity orbits.
> Asteroids are differentiated rocky or iron bodies that were
> formed or
> trapped in orbit between Mars and Jupiter.
>
> It is quite correct to distinguish between the two types of
> bodies. The
> confusion comes from the likelihood that some comets have
> ended up in
> asteroidal orbits, and have lost their volatiles. And also,
> that
> gravitational perturbations have put some asteroids into
> more comet-like
>
> orbits. It isn't that these aren't very different
> objects, but that in
> some cases we are uncertain about an object's true
> classification.
> Additionally, we know little about composition. A burned
> out comet may
> or may not be similar to an asteroid from a mineralogical
> standpoint.
>
> Chris
>
> *****************************************
> Chris L Peterson
> Cloudbait Observatory
> http://www.cloudbait.com
>
>
> ----- Original Message -----
> From: "Mark Ford" <mark.ford at ssl.gb.com>
> To: <Meteorite-list at meteoritecentral.com>
> Sent: Thursday, May 22, 2008 3:42 AM
> Subject: Re: [meteorite-list] Observed lunar meteorite
> impacts hit 100
>
> > Good point Larry.
> >
> > But I can't understand why people are still
> carefully distinguishing
> > between comets and Asteroids?, I think by now we can
> assume they are
> > basically one and the same, and not some exotic
> different species. To
> > me
> > it's just that some rocks are more 'wet and
> oily' than others...
> >
> > I'd find it very very hard to believe there are no
> pieces of comet in
> > our collections.
> >
> > Best,
> > Mark Ford
> -list
>
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Received on Thu 22 May 2008 07:12:01 PM PDT