A certain asteroid has 100% morale, 0% crime, a civilisation level of 66%, tax rate of 5%, an ER of 1.08, and 0 credits in planetary income.

Since I don't understand the fancy math formula for calculating planetary income, my simplistic theory is that there is no planetary income because the ER needs to be around 1.5. Is that explanation close enough?

If a planet has 0 credits planetary income, then that means there is a lack of facilities present to completely fill in the planetary income equation. For example, if there are only skyscrapers and power generators present there.