Comets smell like rotten eggs. A comet smells like rotten eggs, urine, burning matches, and… almonds. Traces of hydrogen sulphide, ammonia, sulphur dioxide, and hydrogen cyanide were all found in the makeup of the comet 67P/Churyumove-Gerasimenko. Promotional postcards were even commissioned in 2016 carrying the pungent scent of a comet.