Which event may have disturbed the original dust cloud and helped form the solar nebula that led to the Sun and planets?

• A. A supernova explosion
• B. A planetary collision
• C. A solar flare
• D. A meteor shower

Answer: (A)

A nearby supernova explosion can send a powerful shock wave through the interstellar medium, compressing a nearby cloud of gas and dust just enough to overcome internal pressure and start collapsing under gravity. That collapse creates a solar nebula—the rotating disk of material that eventually forms the Sun and the surrounding protoplanetary disk from which planets grow. In addition, the material from the dying star can seed the nebula with short-lived radioactive elements, which meteorite evidence supports as part of our solar system’s early makeup.

A planetary collision would happen after a solar system has formed and isn’t capable of disturbing the original dust cloud enough to trigger the initial collapse. A solar flare is a surface event on a star and acts on material close to the star, not on the vast cloud needed to form a new star. A meteor shower involves small particles entering a planet’s atmosphere and likewise cannot disturb a large, distant dust cloud.