Which molecule serves as the essential 'workhorse tracer' for mapping molecular clouds?

Answer

Carbon monoxide (CO)

Because $ ext{H}_2$ is hard to detect, scientists rely on $ ext{CO}$, which is abundant enough and produces detectable energy emissions that can be mapped using radio telescopes.

Which molecule serves as the essential 'workhorse tracer' for mapping molecular clouds?
Spaceastronomystar formationmolecular cloud