Voldemort could have travelled to different planets. Muggles landed on the moon, I think Wizards could do that easily.
Why didn't Voldemort hide his Horcruxes on the Moon and/or other planets?
Voldemort could have travelled to different planets. Muggles landed on the moon, I think Wizards could do that easily.
Why didn't Voldemort hide his Horcruxes on the Moon and/or other planets?
There is no evidence that wizards can leave Earth.
Simply: Voldemort didn't hide his Horcruxes on Mars, because he had no way to get there.
In fact, there's only a single reference to space travel in the entire series:
He flicked through the rest of the magazine. Pausing every few pages he read an accusation that the Tuthill Tornados were winning the Quidditch League by a combination of blackmail, illegal broom-tampering, and torture; an interview with a wizard who claimed to have flown to the moon on a Cleansweep Six and brought back a bag of moon frogs to prove it; and an article on ancient runes, which at least explained why Luna had been reading The Quibbler up-side down.
Harry Potter and the Order of the Phoenix, chapter 10: "Luna Lovegood"
We can tell from this that space travel is... not common among wizards, any more than it is among Muggles.