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Some features of Earth (and beyond) have been bugging me for quite some time. When molten rock is beneath the surface, it's called "magma". Above the surface, it is called "lava". When a bolide is in orbit of any planet, it's called a "meteoroid". When it makes contact with the atmosphere, it becomes a "meteor". When it hits the surface, it becomes a "meteorite". But changing one's name based on a change in location is, at best, superficial and has no relation to chemistry and composition.

Are there any REAL differences between magma and lava? Are there any REAL differences between a meteoroid, a meteor and a meteorite? If not, then why do we call them by different names?

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    $\begingroup$ Couldn't the same thing be said about Rain and Water? Different names for where things are and what they do or just did isn't a bad idea, though I will admit that the Meteroid/ite/Meteor to me always seemed a bit unnecessary but I might not feel that way if I was a professional astronomer. Magma/Lava never bothered me. $\endgroup$ – userLTK Jul 4 '16 at 7:29
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    $\begingroup$ Actually, the composition of meteoroid changes when it becomes ad meteor and a meteorite. While being a meteor, most volatile compounds evaporate and chemical organic compounds are destroyed. Hence, the composition of meteoroids and meteorites differs. Moreover, one meteor may break into several parts. There might be more differenceres. $\endgroup$ – daniel.neumann Jul 4 '16 at 10:42
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For magma and lava it's liked you said: "magma" is used under the surface, "lava" above. See for instance the definition of USGS Volcano Hazard Program's glossary:

Lava: General term for magma (molten rock) that has been erupted onto the surface of the Earth and maintains its integrity as a fluid or viscous mass, rather than exploding into fragments.

Now, does this simple location change justify another term? I would argue that yes, for this reason: if all lavas have once been magmas, all magmas will not become lava.

The fate of magmas can vary. Some will form plutons and crystallize inside the crust instead of reaching the surface. Granites, for instance, have once been magmas. This is why the main rock type "magmatic rocks" is subdivided into two subcategories: plutonic rocks and volcanic rocks. Even in the volcanic subcategory, all rocks are not lavas. As the USGS definition suggests, only a magma erupted effusively becomes a lava. A magma erupted explosively generates another type of volcanic rocks: tephra.

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There is a real difference between lava and magma. Magma contains lots of water and various gases. When it reaches earth's surface, it looses most of its volatiles and becomes lava.

So, magma is volatile rich lava.

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  • $\begingroup$ What about the other half of the question? $\endgroup$ – bon Jul 4 '16 at 18:59
  • $\begingroup$ I said all I know... $\endgroup$ – Irakli Skhirtladze Jul 5 '16 at 8:47
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And it is similarly just a naming convention with the meteor* things:

https://spaceplace.nasa.gov/asteroid-or-meteor/en/

and

https://solarsystem.nasa.gov/asteroids-comets-and-meteors/meteors-and-meteorites/in-depth/

Regardless of its composition, when it breaks off from an asteroid or comet, as long as it is in space it is a meteoroid. When it hits the atmosphere, it turns into a meteor, and when it is lying on the ground ready to be taken home or elsewhere and classified by composition, it has converted into a meteorite.

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