(astronomy, planets) Of or pertaining to a protoplanet.

Relating to a stage in the life of a red giant star or its protoplanetary nebula during the star's final stages of life

(astronomy) Alternative form of protoplanetary disk

(astronomy) A rotating disk of dense gas and dust surrounding a young newly formed star, and from which planets may be formed.

(astronomy) A stage in stellar evolution when a star starts to shed its outer layers before coming a true planetary nebula.

plural of protoplanetary nebula

plural of protoplanetary nebula

plural of protoplanetary disc