2015ApJ...809..181W

We present pre-perihelion infrared 8-31 µm spectrophotometric and imaging observations of comet C/2012 K1 (Pan-STARRS), a dynamically new Oort Cloud comet, conducted with NASA's Stratospheric Observatory for Infrared Astronomy facility (+FORCAST) in 2014 June. As a ''new'' comet (first inner solar system passage), the coma grain population may be extremely pristine, unencumbered by a rime and insufficiently irradiated by the Sun to carbonize its surface organics. The comet exhibited a weak 10 µm silicate feature ~=1.18±0.03 above the underlying best-fit 215.32±0.95 K continuum blackbody. Thermal modeling of the observed spectral energy distribution indicates that the coma grains are fractally solid with a porosity factor D = 3 and the peak in the grain size distribution, a_peak= 0.6 µm, large. The sub-micron coma grains are dominated by amorphous carbon, with a silicate-to-carbon ratio of. The silicate crystalline mass fraction is, similar to with other dynamically new comets exhibiting weak 10 µm silicate features. The bolometric dust albedo of the coma dust is 0.14±0.01 at a phase angle of 34.°76, and the average dust production rate, corrected to zero phase, at the epoch of our observations was Afρ ~= 5340 cm.