Detection of Co and ethane in comet 21P/Giacobini-Zinner: Evidence for variable chemistry in the outer solar nebula

Ethane and carbon monoxide were detected in a short-period comet of probabl e Kuiper Belt origin. Ethane is substantially less abundant compared with H yakutake and Hale-Bopp, two comets from the giant-planet region of the sola r nebula, suggesting a heliocentric gradient in ethane in precometary ices. It is argued that processing by X-rays from the young Sun may be responsib le.