Every Snowflake Needs a Speck of Dust and So Do Planets

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A snowflake cannot form out of nothing.

Water vapour will sit in the air quite happily, supercooled and reluctant, until it finds a speck of dust to build on and then it crystallises around it.

Cosmochemists have had a version of that problem for decades.

The early Solar System was a furnace of gas, and the first solid grains had to condense out of it somehow, yet condensing from a perfectly uniform gas is slow and difficult work.

New research from Caltech, analysing fragments of a meteorite that fell over Mexico in 1969, suggests the seeds were already there.

Buried inside the oldest solids we possess are specks of stardust from a star that lived and died before the Sun existed.