Infrared emission by organic grains in the coma of comet Halley

摘要: Spacecraft1 and ground-based2–5 observations of comet Halley in the near-infrared reveal a triple-peaked emission feature near 3.4 µm, characteristic C–H stretching hydrocarbons (–CH3 –CH2– alkanes). Here we discuss transmission spectra organic residues produced by laboratory irradiation candidate cometary ices, which serve as basis for model emitting dust. The synthesis solid residue from irradiated low-occupancy methane ice clathrate simulates radiation processing experienced Halley. spectrum this residue, convolved with simple two-component thermal based on spacecraft-determined dust distribution coma, fits µm feature, provides optical depths excellent agreement those observationally determined, accounts absence features at longer wavelengths (despite their presence typical residues).