What Was Happening in Our Solar System 4.6 Billion Years Ago? About 4.6 billion years ago, our solar system was in its chaotic infancy during the Hadean Eon on Earth (though the solar system itself doesn’t have formal eons). Here’s a breakdown of the key events: 1. Formation of the Sun: A collapsing cloud of gas and dust (a solar nebula) in the Milky Way formed a protostar at the center. Nuclear fusion ignited ~4.6 billion years ago, creating our Sun as a stable main-sequence star. 2. Accretion