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WolfKC
2003-May-17, 10:50 PM
How big does an object have to be to be called an asteroid?
Thanks :)

Glom
2003-May-18, 08:43 AM
I believe it is something like 100m. Below that, it is called a meteroid.

beskeptical
2003-May-18, 10:35 AM
Do you have a source for that Glom? I didn't think there was an official size definition.

Planets
Planetoids
Moons
Asteroids
Meteoroid
Interstellar Dust

I think these are more of a continuum of sizes and overlap some on definitions, but this debate seems to recur.

Meteoroids and asteroids overlap. A Meteoroid has to become a meteor at some point to be called a meteoroid but there isn't a set time frame. It's a meteoroid when it is in space and a meteor when it contacts the atmosphere of a planet, and a meteorite if it reaches the surface. But then no one seems to agree on exactly what is the difference between an asteroid and a meteoroid.

Vermonter
2003-May-18, 02:13 PM
Is there big money in finding an intact meteorite? $_$

Wingnut Ninja
2003-May-19, 01:27 AM
That's why there's so much controversy over the official status of Pluto... planet, or planetoid?

WolfKC
2003-May-19, 06:20 AM
FYI the reason i was asking is just that I heard about a near earth object being close and it was called an asteroid. So I wondered if it has a certain size range. NBD

beskeptical
2003-May-19, 09:38 AM
Is there big money in finding an intact meteorite? $_$

'Intact' isn't the main criteria with the exception of some 'oriented' ones that didn't tumble as they fell. The value is in the rarity.

There are only 15 or so (I've lost count) Mars rocks so they are very valuable. Moon rocks are valuable. Those in private hands are rare. The US has a very strict policy of not allowing any of the Apollo rocks to get in private hands.

Nickle-iron meteorites sell for about $20.oo/ gram so a hand size rock would cost a few hundred, but it wouldn't make you rich.

http://www.meteorlab.com/ is an online site that sells meteorites. There are a few others. Check the ad pages in 'Sky and Telescope' and 'Astronomy'. There are several for meteorites in every issue.

Grand Vizier
2003-May-19, 11:57 AM
FYI the reason i was asking is just that I heard about a near earth object being close and it was called an asteroid. So I wondered if it has a certain size range. NBD

I think the boundary is fuzzy, but I agree that at some point asteroids fade into meteoroids, so we have three 'm' words:

meteoroid - smallish rock (<10 metres?) encountered in space.
meteor - space rock or ice particle only observed as it vaporises in the Earth's atmosphere (so must be pretty small).
meteorite - space rock that makes it to the Earth's surface.


Then there's that term 'bolide', defined by this source as:



A bolide is a meteor, asteroid, or comet that hits the Earth (or other planet or moon) and explodes.


(from http://www.enchantedlearning.com/subjects/astronomy/glossary/indexb.shtml - note that they oddly say 'meteor', where 'meteoroid' would have been less contradictory, I'd have thought)

(...and would that include 'fireball', usually understood as any small body seen to explode high in the atmosphere - I'd always thought fireball and bolide to be synonymous until I looked them up recently?)

But the other ambiguity that hasn't been mentioned is the boundary line between asteroids and comets. There is a frequently cited theory that some near-earth objects may be the 'clinker' left after dusty comets have finished out-gassing all their volatiles. Of course, confirmation of this will need a few more space missions - though it seems clear from Near/Shoemaker that Eros is a rocky body.

ToSeek
2003-May-19, 04:28 PM
meteor - space rock or ice particle only observed as it vaporises in the Earth's atmosphere (so must be pretty small).

I don't think it has to vaporize to be considered a meteor, so long as it leaves a track. It would still be a meteor until it hits the ground, when it becomes a meteorite.

kilopi
2003-May-19, 04:54 PM
meteor - space rock or ice particle only observed as it vaporises in the Earth's atmosphere (so must be pretty small).

I don't think it has to vaporize to be considered a meteor, so long as it leaves a track. It would still be a meteor until it hits the ground, when it becomes a meteorite.
Most dictionary definitions say that a meteor is the light show, more than the rock itself, although the term meteor can be applied to the rock. A meteor is produced by a meteoroid, in other words. We talked about this before in another thread (Now THAT'S a meteorite (http://www.badastronomy.com/phpBB/viewtopic.php?p=17003&highlight=meteor+meteorite#17003)) and I'd received an email from beskeptical's former professor about it.

Looks like I mispelled "meteoroid" in that old post!

daver
2003-May-19, 05:01 PM
meteor - space rock or ice particle only observed as it vaporises in the Earth's atmosphere (so must be pretty small).

I don't think it has to vaporize to be considered a meteor, so long as it leaves a track. It would still be a meteor until it hits the ground, when it becomes a meteorite.

Three different words, one for the rock before it hits, one for the rock after it hits, one for the light given off as it goes through the atmosphere. Meteoroid, meteorite, meteor. "Meteors" (the streak of light) used to be thought of as atmospheric phenomenon (back when the concepts of rocks falling from the sky was derided), hence its similarity to meteorology.

Glom
2003-May-19, 05:28 PM
beskep, I don't have any good sources, it's just something I remember hearing on The Standard Deviants.

Grand Vizier
2003-May-19, 05:38 PM
Three different words, one for the rock before it hits, one for the rock after it hits, one for the light given off as it goes through the atmosphere. Meteoroid, meteorite, meteor.

Nice one - that's a neat way of putting it. Sadly, we still don't know when a meteoroid becomes an asteroid...

kilopi
2003-May-19, 05:41 PM
Three different words, one for the rock before it hits, one for the rock after it hits, one for the light given off as it goes through the atmosphere. Meteoroid, meteorite, meteor.
There's still some refining to do--for instance, "hits" what? That was the crux of the issue in the book Bad Astronomy. I think the BA gave up on it. :)

And, what do you call the rock when the light is being given off?

daver
2003-May-19, 07:10 PM
There's still some refining to do--for instance, "hits" what? That was the crux of the issue in the book Bad Astronomy. I think the BA gave up on it. :)

I'd vote meteorite if it hits a planet or a moon, leaving off for the moment the definition of what constitutes a planet or a moon. If it hits something smaller, it's open to question. If it hits a star, it's toast.


And, what do you call the rock when the light is being given off?

I'd say it's still a meteoroid--it becomes a meteorite after it hits.

Grand Vizier
2003-May-19, 07:23 PM
I'd vote meteorite if it hits a planet or a moon, leaving off for the moment the definition of what constitutes a planet or a moon. If it hits something smaller, it's open to question. If it hits a star, it's toast.


Ah hah. How about the term 'impactor' here (c.f. the lunar impact hypothesis)? Gives me the feeling that meteorites have to be smallish objects that survive impact with planetary surfaces (and hence can be analysed, put in museums, etc).

(Edited to fix the quote tag)

Psionyx
2003-May-19, 10:12 PM
What, no Moonoids? Moons ALWAYS get the shaft... (NO PUN INTENDED, so just get your minds out of the gutter and into the stars where they belong!)

Grand Vizier
2003-May-19, 11:52 PM
What, no Moonoids? Moons ALWAYS get the shaft... (NO PUN INTENDED, so just get your minds out of the gutter and into the stars where they belong!)

Can't think what you mean :wink: But maybe everything should have an -oid. Satelloids? And Brown Dwarfs could be 'staroids'. OTOH, there's the particle suffix route. A little while back people were referring to 'plutinos' for large KBOs. Planetinos and starinos both sound good...

kilopi
2003-May-20, 12:16 AM
I'd vote meteorite if it hits a planet or a moon, leaving off for the moment the definition of what constitutes a planet or a moon.
Actually, what I was searching for was more firming up of "hit". When the meteoroid encounters the atmosphere, has it "hit" the Earth? If not, are you saying that the atmosphere is not part of the planet? Why not?

Mainframes
2003-May-20, 10:08 AM
I'd vote meteorite if it hits a planet or a moon, leaving off for the moment the definition of what constitutes a planet or a moon.
Actually, what I was searching for was more firming up of "hit". When the meteoroid encounters the atmosphere, has it "hit" the Earth? If not, are you saying that the atmosphere is not part of the planet? Why not?

I'd probably cop out and go for the sequence of entering the atmosphere and then hitting the surface, but it does beg the question that if an object skims off the atmosphere has it technically hit the planet or not?

kilopi
2003-May-20, 01:23 PM
I'd probably cop out and go for the sequence of entering the atmosphere and then hitting the surface, but it does beg the question that if an object skims off the atmosphere has it technically hit the planet or not?
IIRC, in the BA's book, the contention was over one that had hit an airplane in flight. What is that? :)

daver
2003-May-20, 07:23 PM
I'd vote meteorite if it hits a planet or a moon, leaving off for the moment the definition of what constitutes a planet or a moon.
Actually, what I was searching for was more firming up of "hit". When the meteoroid encounters the atmosphere, has it "hit" the Earth? If not, are you saying that the atmosphere is not part of the planet? Why not?

If the meteoroid was made of flubber and hit the earth and bounced off to continue on its merry way, i wouldn't consider it a meteorite. If a meteoroid skimmed through the atmosphere enough to lower its velocity to less than escape velocity but still remained in orbit (not for very long, mind you), i wouldn't consider it a meteorite until it was no longer orbiting.. I think that to be a meteorite, it has to collide with the planet and stay there. If the meteoroid was a hollow sphere filled with hydrogen, if it collided with the atmosphere, was captured, but due to its extremely low density never descended to the ground, i suppose i'd consider it a meteorite.

daver
2003-May-20, 07:29 PM
I'd probably cop out and go for the sequence of entering the atmosphere and then hitting the surface, but it does beg the question that if an object skims off the atmosphere has it technically hit the planet or not?
IIRC, in the BA's book, the contention was over one that had hit an airplane in flight. What is that? :)

Anti aircraft asteroid? If it were moving at less than orbital velocity, i'd go ahead and call it a meteorite.

nebularain
2003-May-21, 05:17 AM
Meteoroid - Small chunk of rock and/or metal in space (whatever the size parameters are - like what separates a "rock" from a "boulder?")

Meteor - Particle or small rock producing a streak through the atmosphere (Of course, the question here, then, is do we consider "space junk" producing a streak across th atmosphere a meteor or not?).

Meteorite - Small chunk of rock and/or metal that came through Earth's atmosphere and is producing a streak across the sky and come to rest relative to whatever it impacted (so, if it hit and came to rest in/on the plane, it is no longer producing a streak and relative to the plane it has come to rest).

How's that?

daver
2003-May-21, 10:32 PM
Meteor - Particle or small rock producing a streak through the atmosphere (Of course, the question here, then, is do we consider "space junk" producing a streak across th atmosphere a meteor or not?).

Well, according to my recollection of my astro classes, "meteor" technically refers to the light given off, not to the object itself.

kilopi
2003-May-22, 02:04 AM
Well, according to my recollection of my astro classes, "meteor" technically refers to the light given off, not to the object itself.
As it should. That is the definition that you find in most dictionaries. However, a lot of dictionaries also report the common use of the term to refer to the rock itself, or anything associated, as in "meteor noise".

Peace_Rules
2003-May-24, 07:27 AM
How big does an object have to be to be called an asteroid?
Thanks :)


Potentially Hazardous Asteroids (PHAs) are space rocks larger than approximately 100m that can come closer to Earth than 0.05 AU.

I hope that's the answer you were looking for.