Ice, Ice, Maybe? Investigating 46P/Wirtanen’s Inner Coma for Icy Grains

Theodore Kareta, John W. Noonan, Walter M. Harris, Alessondra Springmann

Research output: Contribution to journalArticlepeer-review

2 Scopus citations


The release of volatiles from comets is usually from direct sublimation of ices on the nucleus, but for very or hyperactive comets other sources have to be considered to account for the total production rates. In this work, we present new near-IR (NIR) imaging and spectroscopic observations of 46P/Wirtanen taken during its close approach to Earth on 2018 December 19 with the MMIRS instrument at the MMT Observatory to search for signatures of icy or ice-rich grains in its inner coma that might explain its previously reported excess water production. The morphology of the images does not suggest any change in grain properties within the field of view, and the NIR spectra do not show the characteristic absorption features of water ice. Using a new Markov Chain Monte Carlo-based implementation of the spectral modeling approach of Protopapa et al., we estimate the areal water ice fraction of the coma to be <0.6%. When combined with slit-corrected Af ρ values for the J, H, and K bands and previously measured dust velocities for this comet, we estimate an icy grain production rate of less than 4.6 kg s−1. This places a strict constraint on the water production rate from pure icy grains in the coma, and in turn we find that for the 2018-2019 apparition approximately 64% of 46P’s surface was actively sublimating water near perihelion. We then discuss 46P’s modern properties within the context of other (formerly) hyperactive comets to understand how these complex objects evolve.

Original languageEnglish (US)
Article number85
JournalPlanetary Science Journal
Issue number5
StatePublished - May 1 2023

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Geophysics
  • Earth and Planetary Sciences (miscellaneous)
  • Space and Planetary Science


Dive into the research topics of 'Ice, Ice, Maybe? Investigating 46P/Wirtanen’s Inner Coma for Icy Grains'. Together they form a unique fingerprint.

Cite this