Scientists estimate solar nebula’s lifetime
About 4.6 billion years ago, an enormous cloud of hydrogen gas and dust collapsed under its own weight, eventually flattening into a disk called the solar nebula. Most of this interstellar material contracted at the disk’s center to form the sun, and part of the solar nebula’s remaining gas and dust condensed to form the planets and the rest of our solar system. Now scientists from MIT and their colleagues have estimated the lifetime of the solar nebula — a key stage during which much of the solar system evolution took shape. This new estimate suggests that the gas giants Jupiter and Saturn must have formed within the first 4 million years of the solar system’s formation. Furthermore, they must have completed gas-driven migration of their orbital positions by this time. “So much happens right at the beginning of the solar system’s history,” says Benjamin Weiss, professor of earth, atmospheric, and planetary sciences...