How asteroids become "rock"?

you ask a very good question, and the interpreted reason (the one that seems to make the most sense) is that many (perhaps most?) asteroids are from the destruction of a planetary body. Meteors (and asteroids, as far as we can tell, not that we have actually sampled one directly) tend to come in several types which are very similar to the different layers of the earth, iron (core), stony iron (mixture of core and mantle materials) and chondrites (the mantle and perhaps crust). For this to be, does require that the asteroids and smaller meteors came from a planet that did in fact undergo melting and metamorphism and segregation of materials after formation.

And you will probably recognize that comets, unlike asteroids, do tend to be an amalgamation of space debris rather than solid and massive. This underlines the difference in origin between asteroid and comet.

This does not mean that some meteor or asteroid materials could not have formed in space from the process of collisional heating or passing near to the sun and so forth, but it does explain a large proportion of the asteroids derived from the asteroid belt: they were once part of a planetary body that somehow got destroyed.

An interesting question that has a fairly recent and serendipitous answer. This is true. It doesn't seem like gravity ought to pull dust together to create asteroids, yet they exist. One of the astronauts on the ISS was fooling around with a bag of coffee creamer and shook it up a little. When another astronaut looked over he immediately realized that the small clumps that almost immediately formed were as a result of their electrostatic charge. "Hey, you just solved a huge question without even realizing it."

From there over unimaginable periods of time, the jostling, and gravity solidify it into rock. Certainly Iron, being able to carry a charge and having greater mass is more likely to go through this process faster and create n asteroid.

Here's the article in Sky & Telescope

http://www.skyandtelescope.com/astronomy-news/buil...

Some asteroids are believed to be 'rock piles' - a collection of rocks held together loosely by their own gravity. Some are believed to have been blasted out of a planet through impacts by other bodies. Others are believed to be rocks held together by ice. It's possible (take the collision of Earth and Theia) that molten chunks of material were blasted into space, which stuck together, cooling rapidly - forming the small bodies we see.

It's one of the reasons why the Orion capsule's targets is the asteroid belt - to get samples of different asteroids to determine what they're made of, and how they came to be.

How asteroids become "rock"?

It's a phenomena known as vacuum welding or vacuum cementing. Small particles will cement themselves together under high vacuum conditions. This effect has caused small moving parts of some satellites to fuse together and preventing them from functioning.

It is one reason why its believed it would be more efficient to run some industries in space.

Also called cold welding.

Most asteroid are NOT believed to have been caused this way. It is thought that the asteroid are actually parts of a planet that was somehow destroyed.

Even so, the GRAVITY of all those small piece of dust is enough to hold them together, and the millions of years of "baking" in the raw radiation from the sun is enough to fuse the dust into rock.

The assumption is that a planet formed in the area or moon wandered in after being hit in early solar system development then the body broke up under gravitational forces because of its location in the system.

They get sprinkled with Ziggy Stardust.

dust is rock particles

Actually scientists do not understand this process...