Are comets (as far as we can tell) all ice - or do we find cores of heavier elements (metals)?

Question

Iron, etc.

How have we determined one way or another (if we have)?

Answer 1

we can tell the composition by the the way light interacts with the comets tail primarily.

http://en.wikipedia.org/wiki/Astronomica...

comets are composed of many different things.

Many comet questions you might like this link:

http://www2.jpl.nasa.gov/sl9/

This gives an idea about the power in comets.

Answer 2

Comets are made of several distinct parts: first of all, there is a solid snowball, called nucleus, made of dust and ice. It is mostly formed of ice and gas with a small amount of dust and other solids like hydrocarbons. When the comet comes near the Sun, the nucleus heats up and becomes active, causing volatile gas to sublime. The released gas and dust form a cloud, or coma, a dense atmosphere surrounding the nucleus, made of a cloud of water, carbon dioxide and other neutral gases as well as dust grains. The coma is later swept into the elongated tails and a huge but very sparse hydrogen cloud (that can measure up to millions of km in diameter).

The dust contains elements such as iron and other things. But there are small numbers.

regardslHella

Answer 3

We also find cores of heavier elements.  Some comets have stopped having a tail.  Some asteroids have been found to have tails from time to time.  So, it appears that at least some comets have a non-icy core, which looks something like an asteroid once the ice is gone.