Seeing your image above I can see sorta what effect you are going for. What I would probably do is create a sphere. Kind of shape it like an M&M and apply the green lit materials from the miscellaneous or complex section. You can color it to what you are looking for and perhaps dim the opacity and add another smaller version as the core. Could also put a little light in the center. That should help some. One thing to worry about is the light bouncing off of nearby planets and such sometimes. Could also stretch out the sphere so it trails better. I hope that helps and sorry about rambling .. need to wake up ...