Firstly, I consider this riddle to be a fascinating one. The answer is Earth. Our Earth is formed with atoms and molecules which collided with each other to form a huge chunk of rock which we name as the Earth. The neighbor,as highlighted by the riddle, is the Sun. Sun provides us heat and light energy which impacts our daily lives. Thereby, this riddle clearly states that the answer is the 'Earth'.
Ps- I accord importance to this question and hope my answer is marked as the brainiest answer. Also, I appreciate such riddles which tests our knowledge about riddles!