Our solar system formed about 4.6 billion years ago from a collapsing cloud of gas and dust. The Sun contains over 99 percent of the total mass of the solar system and provides the energy that sustains life on Earth. The eight planets orbit the Sun in roughly circular elliptical paths, from Mercury closest to the Sun to Neptune farthest away. Mars has been the target of numerous robotic missions seeking signs of past or present life. Jupiter is the largest planet and its Great Red Spot is a storm that has persisted for centuries. Astronomers have discovered thousands of exoplanets orbiting other stars, some of which may harbor conditions suitable for life.