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Why are novae not considered likely sources of planetary nebulae?

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Planetary nebula Southern Ring Nebula as captured by the James Webb Space Telescope in the near-infrared (left) and the mid-infrared (right). The dimmer star at the center of this scene has been sending out rings of gas and dust for thousands of years in all directions. The Southern Ring Nebula is approximately 2,500 light-years away.

Novae are not considered likely sources of planetary nebulae primarily due to the nature and velocity of their ejecta. While planetary nebulae are formed by the relatively slow expansion of material—typically 24–56 km (15–35 miles) per second—the shells ejected by novae expand at speeds of hundreds of kilometres per second.12

Furthermore, the physical processes involved in these phenomena differ significantly. A planetary nebula is created when a red giant star undergoes a period of instability, leading to the ejection of its outer layers and the eventual exposure of its hot core. In contrast, a nova is an explosive event occurring in a close binary star system, where a white dwarf accumulates hydrogen-rich material from a companion star until a nuclear explosion occurs on its surface. Because the expansion characteristics and the evolutionary mechanisms of novae do not align with the observed properties of planetary nebulae, they are excluded as candidates for their origin.324