How fast do planetary nebulae expand?

Planetary nebulae typically expand at speeds ranging from 24 to 56 kilometers (15 to 35 miles) per second.1

During the early stages of a nebula's evolution, the apparent expansion can be more complex. As the ionization zone moves outward through the stellar wind, the nebula may appear to expand faster than the individual gas atoms are moving, as the ionized shell effectively "eats into" the surrounding neutral material. Once the entire mass of gas is ionized, the expansion is driven entirely by the motion of the gas.2

Because the gravitational pull of the central star is minimal at the distance of the shell, this expansion continues until the nebula eventually merges with the surrounding interstellar gas. By dividing the nebula's radius by its expansion speed, astronomers can estimate the age of the nebula since its ejection, which typically ranges up to approximately 30,000 years.13