[RightWhale]

A molecular cloud. Mostly hydrogen--H2. Right?

[petuniasevan]

Right!

What are Giant Molecular Clouds composed of?

• The interstellar medium is roughly 99% gas, 1% dust by mass

• Of the gas, roughly 90% is hydrogen (H2 and H), and 10% is helium, with some CNO-based gases (i.e. hydrocarbons)

• Ice grains composed of CN0-based molecules (mainly water, ammonia, CO, etc.)

• Dirty sub-micron-sized grains of magnesium and iron silicates