http://www.psrd.hawaii.edu/Nov08/chondrule_sodium.html ..

1
Tiny Molten Droplets, Dusty Clouds, and Planet
Formation

• 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.
2
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

3
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