How long did it take to form the planets?

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Accepted Answer

Asteroid-sized bodies formed within about the first few million years, Mars largely within about 10 million years, and Earth over roughly 30 to 100 million years.

Meteorites and planetary samples reveal a surprisingly fast timeline for planet formation.

Time zero. The oldest solids, CAIs, formed about 4,567 million years ago. Scientists use this as the start of the Solar System.

First planetesimals. Hafnium–tungsten dating of iron meteorites shows that some metal cores separated within about 1 million years after CAIs. This means planetesimals tens to hundreds of kilometres across formed very quickly.

Chondrules and chondrite parent bodies. Most chondrules formed about 1 to 3 million years after CAIs, and the parent bodies of chondrites assembled around 2 to 4 million years.

The gas disc. Observations of young stars suggest gas discs last a few million years. Evidence from meteorite magnetism suggests the solar nebula's gas largely disappeared within about 4 million years, so giant planets like Jupiter must have formed before then.

Mars. Tungsten isotopes in Martian meteorites suggest Mars grew to roughly its present size within about 2 to 10 million years. Mars may be a planetary embryo that never grew further.

Earth and the Moon. Earth took longer, growing through collisions between embryos. Its core formed over roughly 30 to 100 million years, and the giant impact that formed the Moon is commonly dated to between about 30 and 150 million years after CAIs, with estimates still debated.

This timeline has been established largely through careful analysis of meteorites, combined with computer models of how dust and planetesimals grow.

How long did it take to form the planets?

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