A Wandering Jupiter Shaped The Solar System, And Now We Know When it Happened

When compared to the outermost planets in our solar system, the four planets closest to the sun — Mercury, Venus, Earth and Mars — are quite small. Astronomers believe this is because a massive planet, most likely a young Jupiter, may once have wandered through the inner reaches of our star system, sweeping up much of the material needed for the four rocky planets to become supersized.