In the outer regions of the solar nebula, which condensed as ices due to low temperatures, in addition to rock and iron?

• A. Helium compounds condensed as ices
• B. Hydrogen compounds condensed as ices
• C. Water and rocks only condensed
• D. Silicates condensed as ices

Answer: (B)

In the cold outer solar nebula, temperatures were low enough for volatile, hydrogen-bearing compounds to freeze onto dust grains, forming ices alongside the solid rock and iron grains that already existed as refractory materials. This means substances like water, ammonia, and methane could condense into icy grains, enriching the icy bodies that formed there. Helium, on the other hand, remains a gas because it does not readily form stable ices under these conditions. Silicates are rocky minerals, not ices, so they aren’t condensed as ices. Water and rocks only would miss the important icy component provided by hydrogen compounds.