Please choose the correct answer to the question: Uranus is one of the outer planets of the solar system. The average distance of Uranus from the Sun is 2.87 billion kilometers. Which best explains why Uranus revolves in its orbit instead of moving out into space?

Answer1: The orbit of Neptune limits Uranus. Answer2: Gravity pulls Uranus toward the Sun. Answer3: Electromagnetic energy pulls on Uranus. Answer4: Other planets have the same mass as Uranus.

Answer format: answer1/answer2/answer3/answer4