SOFIA Infrared Spectrophotometry of Comet C/2012 K1 (Pan-STARRS)

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, apeak = 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.