  Hyperactive comets have high water production rates, with inferred
sublimation areas of order the surface area of the nucleus. Comets 46P/Wirtanen
and 103P/Hartley 2 are two examples of this cometary class. Based on
observations of comet Hartley 2 by the Deep Impact spacecraft, hyperactivity
appears to be caused by the ejection of water-ice grains and/or water-ice rich
chunks of nucleus into the coma. These materials increase the sublimating
surface area, and yield high water production rates. The historic close
approach of comet Wirtanen to Earth in 2018 afforded an opportunity to test
Hartley 2 style hyperactivity in a second Jupiter-family comet. We present high
spatial resolution, near-infrared spectroscopy of the inner coma of Wirtanen.
No evidence for the 1.5- or 2.0-$\mu$m water-ice absorption bands is found in
six 0.8-2.5 $\mu$m spectra taken around perihelion and closest approach to
Earth. In addition, the strong 3.0-$\mu$m water-ice absorption band is absent
in a 2.0-5.3 $\mu$m spectrum taken near perihelion. Using spectroscopic and
sublimation lifetime models we set constraints on the physical properties of
the ice grains in the coma, assuming they are responsible for the comet's
hyperactivity. We rule out pure water-ice grains of any size, given their long
lifetime. Instead, the hyperactivity of the nucleus and lack of water-ice
absorption features in our spectra can be explained either by icy grains on the
order of 1 $\mu$m in size with a small amount of low albedo dust (greater than
0.5% by volume), or large chunks containing significant amounts of water ice.
