Chondrules: –Millimeter-sized droplets –Formed by melting in the solar nebula Sodium (Na) should have been lost at high temperature because it is so volatile and chondrules were surrounded by a low- pressure gas Was it lost? Photomicrograph in polarized light. Black is glass, colored crystals are olivine. Tiny Molten Droplets, Dusty Clouds, and Planet Formation

Tiny Molten Droplets, Dusty Clouds, and Planet Formation Na in olivine records crystallization and loss to surroundings Concentration in single crystals (squares) suggests variation caused by crystallization (dashed line), not Na loss Na loss would appear as low Na in olivine, except at the very edge of the crystals (line) So, no Na loss

Tiny Molten Droplets, Dusty Clouds, and Planet Formation To prevent Na loss, need to have enough Na in surrounding gas to prevent diffusion out of the hot chondrules This requires concentrating dust to yield a cloud density of tens to thousands of grams per cubic meter Mechanism for doing this is not worked out yet High dust densities could have triggered formation of planetesimals Asteroid Eros, 33x13x13 km, may be a fragment of a chondrite planetesimal