They will be separate layers. Don’t put Particular and Element on the same layer.
You’ll have to get clever about how it works. Once you get it looking the way you want, you may need to duplicate your layer of Particular and put one below and one above the E3D layer and use the distance visibility settings to trim them to show up where they’re supposed to.
Alternatively, you can use a depth pass from Element and have one copy of Particular above the main E3D layer.
As to getting them to look like they’re emitting from the asteroid/comet/meteor, just a spherical emitter will probably do the trick, but you can also load 3d objects into Particular as an emitter source.
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