  Jupiter family comet 17P/Holmes underwent a remarkable outburst on UT 2007
Oct. 24, in which the integrated brightness abruptly increased by about a
factor of a million.We obtained near infrared (0.8 - 4.2 micron) spectra of
17P/Holmes on UT 2007 Oct. 27, 28 and 31, using the 3.0-m NASA Infrared
Telescope Facility (IRTF) atop Mauna Kea. Two broad absorption bands were found
in the reflectance spectra with centers (at 2 micron and 3 micron,
respectively) and overall shapes consistent with the presence of water ice
grains in the coma. Synthetic mixing models of these bands suggest an origin in
cold ice grains of micron size. Curiously, though, the expected 1.5 micron band
of water ice was not detected in our data, an observation for which we have no
explanation. Simultaneously, excess thermal emission in the spectra at
wavelengths beyond 3.2 micron has a color temperature of 360 +/- 40 K
(corresponding to a superheat factor of ~ 2.0 +/- 0.2 at 2.45 AU). This is too
hot for these grains to be icy. The detection of both water ice spectral
features and short-wavelength thermal emission suggests that the coma of
17P/Holmes has two components (hot, refractory dust and cold ice grains) which
are not in thermal contact. A similarity to grains ejected into the coma of
9P/Tempel 1 by the Deep Impact spacecraft is noted.
