Comet Halley's gas composition and extended sources: Results from the neutral mass spectrometer on Giotto

The Neutral Mass Spectrometer on the Giotto Spacecraft established that H2O is the dominant species in Comet Halley's volatiles and determined the abundance of more than 10 parent species. The instrument discovered strong extended H2CO and CO sources in the coma of Corner Halley. Polymerized H2CO associated with the cometary dust and evaporating slowly as the monomer is most likely the extended H2CO source. Photodissociation of the H2CO into CO fully accounts for the extended CO source.