Volcanoes in the Solar System

Currently in the solar system, we have volcanoes on earth. And then there's three other places where we've seen this kind of activity,. There is a moon of neptune, which is called triton. There is insolatus, which sounds like a salad, but actually the sixth largest moon of saturn. None of those places have active volcanoes. I guess what makes us special ton here earth? What is it about earth and lets still have volcanoes? That's not something we really understand. It's something we're still studying.