What is the smallest planet that can have ...

An Earth like atmostphere...
A venusian type atmosphere
An ocean without continents

and are asteroids full of metals? Or are those always meteors?

Oh and are there different types of gas giants, other than just size...

[QUOTE=Durakken;1613770]What is the smallest planet that can have ...

An Earth like atmostphere...?

>>> Smaller than Earth planets can retain a useful atmosphere. Having enough mass to hold an atmosphere against the solar winds would be the decider.

A Venusian type atmosphere...?

>>> Same as above. The composition of a atmosphere would depend upon the gasses available.

An ocean without continents...?

>>> That would be dependent on conditions being tolerant to the formation of oceans. Uniformity of surface and water depth, Not planet size.

and are asteroids full of metals...?

>>> No. some are rubble, ice, and not all rock is metallic.

Or are those always meteors...?

>>> An asteroid becomes a meteor only after entering Earths atmosphere. They only become meteorites after reaching the surface.

Oh and are there different types of gas giants, other than just size...?

>>> Yes, many.

Are you looking for diameter or mass? Then again, it may not matter as those results are dependent upon factors other than size. The atmospheres of Earth and Venus are due to complex processes of weathering, life, tides, having a moon, having a dynamo and magnetosphere, having an appropriate period or rotation and other complex geology that may or may not require a mars sized impactor that creates a moon from continental material that would otherwise land-lock the surface and possibly prohibit plate tectonics.

__________________
"What you think you thought you saw you did not see." Agent J, MiB - Manhatten Bureau

Does Ceres qualify for this last?

I'd say Titan has an earth like atmosphere, at least an earth like density.

I'd say Europa would have an ocean without continents, at least for awhile if it warmed up. But then it would lose the water to space.

Those are the smallest bodies that meet the criteria that I can think of.

__________________
"I'm as accurate as any psychic. And I'm a cartoon!" -- Squidward

"Arrrgh, the laws of physics be a harsh mistress!" -- Bender

What about Triton?

If you knew the distance from a star and diameter of a planet could you tell how many people and say metals are in the planet?

Certainly not. Earth had the same distance and the same diameter a million years ago, but no people whatsoever.

I mean that, if it were populated, could you determine the max size of it's population... like we say the population on earth will level off at about 9 billion. Is there any way to calculate that based on kilometers of land available?

No. For example, were people all vegans, we could probably support about five times the current population with the same overall levels of agricultural productivity; a purely carnivorous population would probably be limited to something like a tenth of the current population. Much smaller or much larger creatures in the human-equivalent niche would complicate the issue. Were the occupiers of the human-equivalent niche eusocial, it's possible that factor, alone, would permit an order of magnitude larger population.

In other words, too many variable parameters.

For a simple comparison here on Earth, compare the populations of China, USA, Canada and Australia. All big countries of similar area.

Or compare the population densities possible with hunter-gather populations vs those with settled agriculture. Without changing any physiological parameters, I'd estimate that the possible human population of the Earth could be limited to as little as a few tens of million to several tens of billions.

In other words, any quess is likely to be correct, with a margin of error of 3 magnitudes.

__________________
"What you think you thought you saw you did not see." Agent J, MiB - Manhatten Bureau