  We present mid-infrared observations of comet P/2016 BA14 (PANSTARRS), which
were obtained on UT 2016 March 21.3 at heliocentric and geocentric distances of
1.012 au and 0.026 au, respectively, approximately 30 hours before its closest
approach to Earth (0.024 au) on UT 2016 March 22.6. Low-resolution
($\lambda$/$\Delta \lambda$~250) spectroscopic observations in the N-band and
imaging observations with four narrow-band filters (centered at 8.8, 12.4, 17.7
and 18.8 $\mu$m) in the N- and Q-bands were obtained using the Cooled
Mid-Infrared Camera and Spectrometer (COMICS) mounted on the 8.2-m Subaru
telescope atop Maunakea, Hawaii. The observed spatial profiles of P/2016 BA14
at different wavelengths are consistent with a point-spread function. Owing to
the close approach of the comet to the Earth, the observed thermal emission
from the comet is dominated by the thermal emission from its nucleus rather
than its dust coma. The observed spectral energy distribution of the nucleus at
mid-infrared wavelengths is consistent with a Planck function at temperature
T~350 K, with the effective diameter of P/2016 BA14 estimated as ~0.8 km (by
assuming an emissivity of 0.97). The normalized emissivity spectrum of the
comet exhibits absorption-like features that are not reproduced by the
anhydrous minerals typically found in cometary dust coma, such as olivine and
pyroxene. Instead, the spectral features suggest the presence of large grains
of phyllosilicate minerals and organic materials. Thus, our observations
indicate that an inactive small body covered with these processed materials is
a possible end state of comets.
