A collapsing cloud of gas and dust starts to spin
What happened
The Solar System started as a cold, slowly turning cloud of gas and dust, mostly hydrogen and helium left from the Big Bang, salted with heavier elements that earlier stars had forged and scattered when they died. NASA's account has the collapse begin when the shockwave from a nearby exploding star, a supernova, swept through a denser pocket of the cloud and set it contracting under its own gravity. As the cloud fell inward it spun faster and flattened, the way a skater speeds up by pulling in their arms, until almost all of the material had piled into a hot, dense center. That center became the young Sun.
Why it matters
The gas and dust that did not fall into the Sun stayed behind as a spinning disk. Every planet, moon, asteroid, and comet, the Earth included, was built from that disk, out of the exact mix of elements the original cloud held.
How we know
The composition of the cloud survives in the oldest meteorites, whose element mix closely tracks the Sun's outer layers. The supernova trigger is the explanation NASA gives for what set a slowly turning cloud collapsing, and the flat, one-directional layout of the planets' orbits today still records that early spinning disk.
Sources
- NASA (Astrobiology Program). How did our Solar System form? (2024) · Reputable sourcescience.nasa.gov · The domain "science.nasa.gov" is on our Reputable source registry. · Link is live and its text matches the event's key terms (Jul 2026)
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Related timelines
- Big Bang to Now → · Zoomed out: this is the spine's 'The Sun and Solar System form'