Condensation
Condensation is the formation of solid grains directly from a cooling gas, the first step in making planets.
Condensation is when a gas turns into a liquid or solid as it cools, as frost forms on a cold window. In the early Solar System it was the process that created the first solid material.
The gas around the young Sun was hot near the centre and cooler farther out. As it cooled, different minerals appeared in a predictable order, known as the condensation sequence. Calculations show that oxides of aluminium, calcium and titanium, such as corundum, hibonite and perovskite, come first, at roughly 1,400 to 1,500 °C at the low pressures of the disc. Next come melilite, spinel and calcium-rich pyroxene, then metal, then olivine and pyroxene, and finally, at much lower temperatures, sulfides and ices.
Calcium-aluminium-rich inclusions in chondrites match the earliest part of this sequence closely, which is why they are thought to be among the first solids. Elements are described as refractory or volatile according to where they fall in the sequence.
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