We can interpret this amazing image of a forming solar system (HL Tauri, from the Alma array; ESO 2014).
Iron meteorites with #taenite and #kamacite domains forming a Widmanstätten pattern tell us that in systems like this or our own solar system:
–planetesimals had already formed and differentiated, while a heat source (decay of 26-Al) was still available.
–they were on the order of 100's of km in diameter, with enough rock to insulate the slowly-cooling core.


