I was born and raised into a Catholic denomination of religion. Therefore, I was raised with having the beliefs, that God did not just create the world, but the entire universe in just 7 days. A lot of people tend to having differing opinions about this subject, so mine is stricly my opinion and belief.
I will answer this in a non-religious point-of-view by not referring to scripture. Logically, if an omnipotent and omniscient entity created the planet Earth, it is only reasonable to assume this entity also created the other planets and probably even the universe. It is not feasible to assume the idea that this all-powerful being only created a single planet when there are others within the same system. It is logical to assume whomever created Earth also created the rest of the solar system. From there you can then argue if that entity created the solar system within this galaxy probably then made the galaxy. If that entity could create the galaxy where the rest of its creations are, what would stop the idea and possibility that this being also created the universe in its entirety. The idea that God created the universe is completely valid.
1 The heavens declare the glory of God;
the skies proclaim the work of his hands.
3 When I consider your heavens,
the work of your fingers,
the moon and the stars,
which you have set in place,
4 what is mankind that you are mindful of them,
human beings that you care for them?
If God made earth than I believe it would be reasonable to assume he made the other planets. I would think if there is life on other planets they have their own bible and set of guidelines they live by similar to ours but more suitable for there standards of living.