The "Rotten Egg Nebula" is a unique protoplanetary nebula resulting from the remnants of the red giant OH231.8+4.2. Situated in the Canis Major constellation, it stands out due to the high presence of hydrogen sulfide and sulfur dioxide molecules surrounding the star in transition.

This peculiar name derives from the distinctive chemical composition surrounding the evolving star. Typically, a full-fledged planetary nebula emerges approximately 1000 years after this initial stage in the nebula's evolution.