Of all the things I learned 50 years ago about how planets formed, one idea has surprisingly stood the test of time

We believed back then that the sun and planets formed together out of a spinning disc of gas and dust. Now the Webb Space Telescope has actually given us edge-on views of discs just like we imagined, caught in the act of making themselves into new solar systems.

Meteorites, material from that early epoch of the solar system, have been the focus of my research for those last 50 years. My colleagues and I have collected data for the density, porosity, and many other physical properties for thousands of these space rocks. Rocks. And there’s the rub. Why are they rocks – very well compacted, hard-as-rock rocks?

Our data let us quantify just how well packed our meteorites are: very well packed, for the most part. Typically, meteorites are made from bits of dust, finer than flour, so well packed together that they’ve become solid rock. But if meteorites came from a cloud of gas and dust, what turned the dust into rock? Where did that happen? How did that happen? As one colleague asked me soon after we’d published our first measurements, why do we have meteorites instead of porous dust bunnies?

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