Question

A planetary nebula is

a. a disk-shaped nebula of dust and gas rotating around a relatively young star, within which planets will eventually form.

b. the nebula caused by the supernova explosion of a massive star.

c. the atmosphere of a red giant star slowly expanding away from the star's core to form a shell of gas.

d. a cloud of gas and dust surrounding newly formed planets from which their moons will eventually form.

Answer 1

A planetary nebula is the atmosphere of a red giant star slowly expanding away from the star's core to form a shell of gas.

Step-by-step explanation:

A planetary nebula is not a disk-shaped nebula of dust and gas rotating around a relatively young star, within which planets will eventually form.

It is also not the nebula caused by the supernova explosion of a massive star. Instead, a planetary nebula is the atmosphere of a red giant star slowly expanding away from the star's core to form a shell of gas. The gas in the shell of the planetary nebula glows because of the ultra-violet energy of the central star. The nebula is formed when a low-mass star is nearing the end of its life.