Compared to the interstellar medium, the gases in a planetary nebula will be richer in helium and carbon.

Question

Quizplus · Accepted Answer

Planetary nebulae are formed from the outer layers of a star that has shed its material near the end of its life cycle. This material has undergone nuclear fusion, producing heavier elements like helium and carbon, thus enriching the nebula compared to the more pristine composition of the interstellar medium.

Compared to the Interstellar Medium, the Gases in a Planetary