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

TL;DR

This study presents infrared spectrophotometry of comet C/2012 K1 (Pan-STARRS) using SOFIA, revealing pristine coma grain properties, composition, and dust production characteristics of a dynamically new Oort Cloud comet.

Contribution

First infrared spectral analysis of a dynamically new comet with detailed modeling of coma grain properties and composition using SOFIA observations.

Findings

Comet exhibited a weak 10 micron silicate feature.

Coma grains are fractally solid with high porosity.

Dust composition is dominated by amorphous carbon with some crystalline silicates.

Abstract

We present pre-perihelion infrared 8 to 31 micron 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 (SOFIA) 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 micron 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 micron, large. The sub-micron coma grains are dominated by amorphous carbon, with a silicate-to-carbon ratio of 0.80 (+0.25) (- 0.20). The silicate crystalline mass fraction is 0.20 (+0.30) (-0.10), similar to with other dynamically new comets exhibiting weak 10 micron silicate features. The bolometric dust albedo of the coma dust is 0.14 +/- 0.01 at a phase angle of 34.76 degrees, and the average dust production rate, corrected to zero phase, at the epoch of our observations was Afrho ~ 5340~cm.