Do asteroids have metallic cores, like planets?

What are these space rocks made of?

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Asked by Katherine Taylor

Generally, no. The structure of asteroids and planets is actually quite different. While planets have a clearly defined internal structure, ranging from molten metal cores to rocky or gas based exteriors, asteroids have a much simpler one. Asteroids fall roughly into three groups.

The first of these are the ‘rubble pile’ asteroids. These objects are a collection of small pieces of debris that are bound together by gravity. It is thought that these asteroids probably originate from collisions. The materials can range from tiny grains of sand up to substantial lumps of rock and metal.

The second group are the solid asteroids. This group makes up the majority of asteroids discovered; their solidity indicates that at one point they were molten. This would allow the materials to melt and for one continuous lump rather than the grainy structure seen in ‘rubble piles’.

The last group is a recently discovered ‘double’ structure. These are becoming increasingly more common and arise when two asteroids are bound extremely closely together, often touching. These asteroids have drifted together and now share an orbit around the Sun and each other.

Very few asteroids are large enough to have a structure which has differentiated into the distinct layers, despite still having a high metallic content like some of the planets.

Answered by Josh Barker from the National Space Centre

Image courtesy of NASA

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