Formation and evolution of the Solar System owe its substantially lower mass simply to having formed a few million years after Jupiter, when there was less gas available to consume. T Tauri stars like the young Sun have far stronger stellar winds than more stable, older stars. Uranus and Neptune are thought to have formed after Jupiter and Saturn did, when the strong solar wind had blown away much of the disc material. As a result, those planets accumulated little hydrogen and helium—not more than each. Uranus and Neptune are sometimes referred to as failed cores. The main problem with formation theories for these planets is the
Formation and evolution of the Solar System formation of the Solar System. This period of heavy bombardment lasted several hundred million years and is evident in the cratering still visible on geologically dead bodies of the inner Solar System such as the Moon and Mercury. The oldest known evidence for life on Earth dates to 3.8 billion years ago—almost immediately after the end of the Late Heavy Bombardment. Impacts are thought to be a regular (if currently infrequent) part of the evolution of the Solar System. That they continue to happen is evidenced by the collision of Comet Shoemaker–Levy 9 with Jupiter in 1994, the 2009 Jupiter