What materials are found in Protoplanetary disks?

• A. Volatile gases and refractory solids
• B. Liquid water only
• C. Metallic ore only
• D. Gases only

Answer: (A)

In protoplanetary disks you have both gas and solid material. The gas is the dominant component and is mainly hydrogen and helium, but it also carries volatile molecules like water vapor, carbon monoxide, and other gases. The solid part consists of dust grains made from refractory materials—things like silicates and metals that stay solid at relatively high temperatures. As you go farther from the star, temperatures drop and ices can form, adding icy solids to the mix. So these disks contain volatile gases and refractory solids together, which is why that option best describes the materials present. The other choices are incomplete or misleading because they ignore either the solid dust or the gaseous components that are also present.