You could script something to generate these but it's easy enough with a couple of circles, depending on the level of control and precision you need.
This is just a bunch of concentric circles with a dashed stroke set with 0.1pt dashes:
You can use a width profile to control the size of the dots and simply add a gradient stroke for the color:
If you need more control of the size you can use the Width Tool. It's harder to finely control the width tool so it would be easier to set the width of a single circle first then duplicate that:
If you want custom shapes rather than dots (as two of your examples use) then you could use a custom brush. It's not ideal though.
Either a scatter brush or a pattern brush would work; a scatter brush is better to control rotation, a pattern brush better for spacing—neither will easily allow you to scale or add a gradient though.
The following is using a pattern brush; you can see that the width profile is squashing the stars rather than scaling them and the rotation of the stars follows the path:
The following is the result of using a scatter brush; the rotation is relative to the page, but we can't affect the scale and the spacing is obviously an issue:
We can manually adjust the spacing on each circle by selecting "Options of Selected Object..." from the Brushes panel dropdown menu and adjusting the spacing:
Since we can't affect the scale of the stars through the brush stroke we will have to do it manually. First expand the strokes so that we have distinct objects. We can then create a selection of our stars with the Lasso Tool and scale each using the Transform Each function (Object → Transform → Transform Each...)
Selecting ever decreasing slices and scaling will give the effect of a gradient of decreasing scale (I've shown 2 selections here but actually did this ~6 times):
Group the result and add a gradient fill: