Hi Alanna! Thanks for your question. The Earth is the only known habitable planet for us humans in this solar system (that we know of). This is because its the only one that has a number of features important for us to live: It is just the right distance away from our Sun to allow the right amount of air, water and heat to support life. Scientists call the position of earth the ‘goldilocks zone’ because its ‘just right’. No other planet has temperatures like Earth that are not too hot and not too cold. Also, no other planet has liquid water like Earth has. Scientists have found that other planets have ice but no liquid water. Finally, Earth has the right mix of chemicals that are required for life (Carbon, Nitrogen, oxygen).
That being said, I believe that we cannot be the only planet in the Universe that has life, because there is a billion, billion galaxies in the universe, each containing millions of stars. We don’t know if any of them contain water and life. But they might!