As you have already selected the correct answer, this is for anyone who want to know the exact steps.
Create your smallest circle using the ellipse tool, then create your biggest circle around it (copy the smaller circle then press ctrl+shift+v to paste in place and hold shift to scale up (On PC)); highlight the two and choose
Object > Blend > Make
This will start the path between the smallest object and the largest. Then select
Object > Blend > Blend Options and choose
Specified Steps to choose the amount of steps you want between your smallest and largest circle:
Once you're happy with the amount of circles, you can select
Object > Expand to release the circles so you can further edit them if you wish: