How could nickle-iron asteroids have formed?

Question

If the sun and planets were formed from a nebula, How did nickel-iron asteroids form in that zero gravity environment? Why aren't ALL asteroids of uniform composition?

I thought the sun was second generation. Regardless, that accounts for the number of elements available, not their distribution.

Of course the metals coalesced. My question was HOW? What forces attracted them together? Gravity should accrete ALL elements equally. And the sun's magnetic field doesn't bunch up anywhere that I am aware of.

Answer 1

The process of getting from supernova residue to asteroids to planets isn't completely understood. My understanding is that certain stages of accumulation are an outstanding problem.

There are some interesting hints that in the rings of Saturn there are radio signals that sound like lightning, that somehow there are static discharges going on in those rings.

http://www.space.com/scienceastronomy/cassini_lightning_040805.html

My guess (and I bear all responsibility if it's wrong and no credit if it's right) is that there are processes involving friction, solar winds and electric attraction that gets the process going until things are big enough for gravity to become a factor.

Answer 2

The protoplanetary nebula had lots of metals in it, since the Sun is pretty much a 5th generation star.

In the mid-plane of the protosolar nebula, interstellar dust grains begin to build up into small gritty particles, made partly of ice and partly of heavy elements. When it gets dense enough, these object rapidly coalesce into boulder-sized or planetoids-sized objects. The density of such objects is high enough that they frequently collide, at very high velocities. This heats them to high temperatures, and the metals within them liquefy and begin to refine themselves away from the gasses and lighter elements, and sink toward the middle. The planetoids may become encorporated into a planet, or they may be smashed apart into asteroids. An asteroid that is mostly made of refined metal has a good chance of surviving subsequent impacts, and so that is the end product of the process, in regions that have not been swept clean by a planet.

Answer 3

You forget that the Sun and its accompanying planetary system is a third generation system. There is at least some supply of the heavier elements because of fusion processes from previous stellar generations and the resultant stellar "deaths".

The rules of accretion do not differentiate between the elements. Some asteroids are chunks of assorted stone and some are "blessed" with more than their portion of nickel-iron. Where did you get the idea that all matter in space was homogeneous?

Answer 4

Hi. I think most people assume that a supernova explodes into gas which cools as it expands. But the metals (elements) should condense into small chunks and, in the turbulent environment, it's not surprising that the would coalesce into larger bodies. What I find MORE interesting is the NON metallic asteroids. Stone is usually more complex than a metal.

Answer 5

As 2 meter man points out, there isn't a well-developed theory on how these materials coalesce. It's possible that the sorting was done by the star that created the elements. Type II supernovae come from stars with iron cores, so maybe that material stays together.

Answer 6

Because of all of the various elements in a proto solar system.

Gravity, cooling, distance from it's parent star, as well as many other things all play roles in the formation of celestial bodies.

Asteroid fields like the one between Mars and Jupiter which may be remnants of a destroyed world should be uniform in their composition.

However other places, like the Kuiper Belt where outside objects maybe have gotten trapped in orbit there, could have different compositions from being created from different parent stars.

Answer 7

They were formed by supernova explosions and most asteroids are made of similar elements, they were not formed in zero gravity environments.

Answer 8

the most likely origion of iron and nickel is the coalescing of molten metals from the early solar system.

Answer 9

wow nice to see how people ponder our universe ! great question !

I was going to answer but the correct answer is there already.