  The gaseous molecular disk that orbits the main sequence A-type star 49 Ceti
has been known since 1995, but the stellar age and the origin of the observed
carbon monoxide molecules have been unknown. We now identify 49 Ceti as a
member of the 40 Myr old Argus Association and present a colliding comet model
to explain the high CO concentrations seen at 49 Ceti and the 30 Myr old A-type
star HD 21997. The model suggests that massive -- 400 Earth mass -- analogs of
the Sun's Kuiper Belt are in orbit about some A-type stars, that these large
masses are composed primarily of comet-like objects, and that these objects are
rich in CO and perhaps also CO2. We identify additional early-type members of
the Argus Association and the Tucana/Horologium and Columba Associations; some
of these stars display excess mid-infrared emission as measured with the
Widefield Infrared Survey Explorer (WISE).
