Nondetection of Water-ice Grains in the Coma of Comet 46P/Wirtanen and Implications for Hyperactivity

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