Possible evidence of hydrocarbons released by the nucleus of Halley's comet.
After subtracting the intense dust-scattered continuum from the original spectra transmitted by the Vega 2 three-channel spectrometer, a broad-band emission emerges in the 342-375 nm spectral range when the cometocentric projected distance p is smaller than 5000 km.  This newly detected emission varies as p-1, which implies that the involved molecule(s) has a parent-type behavior.  The emission band presents four peaks at 347, 356, 364 and 373 nm.  It is tentatively identified as being due to phenanthrene, a three-cycle aromatic condensed hydrocarbon.  A determination of the gQ product, where g is the fluorescence quantum efficiency and Q the production rate gives gQ = 1.2 x 10(25).  If g = 0.012, it comes Q = 1 x 10(27) s-1.  The detection of phenanthrene in Halley's inner coma is an important argument in favor of a similarity of composition between cometary material and interstellar matter.  It supports the hypothesis that comets have kept trace of the interstellar composition through the solar system formation epoch.
Moreels
G
G
Observatoire de Besancon, France.
Clairemidi
J
J
Rousselot
P
P
D001256:Astronomy / Q000379:methods*; D019443:Cosmic Dust; D005118:Extraterrestrial Environment; D019110:Meteoroids; D010616:Phenanthrenes / Q000032:analysis*; D011084:Polycyclic Aromatic Hydrocarbons / Q000032:analysis*; D013026:Space Flight; D018531:Spacecraft / Q000295:instrumentation; D013057:Spectrum Analysis; D014466:Ultraviolet Rays
D019443:Cosmic Dust; D010616:Phenanthrenes; D011084:Polycyclic Aromatic Hydrocarbons; C031181:phenanthrene