I think one good question might deal with the sun's heat and its effect on the planets. Perhaps the question could be phrased like this: What effect does the sun's heat have on each planet and its environment?
The hypothesis would then be based on whatever you believe the answer might be, such as: I hypothesize that the planets located in the center are most likely able to have living things present, while the planets very close to and very far away from are less able.
This could be tested by setting up a high-heat lamp and placing plants in a line, simulating the sun and planets. Recording plant growth would provide evidence.