Coma Volatile Composition and Thermal Physics in Comet C/2022 E3 (ZTF) Measured Near Closest Approach to Earth with NASA-IRTF

TL;DR

This study used near-infrared spectroscopy to analyze the volatile composition and thermal properties of comet C/2022 E3 (ZTF) during its close approach to Earth, revealing molecular abundances, temperature profiles, and spatial distributions.

Contribution

First high-resolution near-infrared spectroscopic measurements of C/2022 E3 (ZTF) providing detailed volatile abundances and thermal profiles at close approach.

Findings

Detected multiple volatile molecules including H2O, CO, and HCN.

Found depletion of most molecules compared to typical Oort cloud comets.

Observed temperature variations indicating icy grain sublimation in the coma.

Abstract

The 2023 perihelion passage of comet C/2022 E3 (ZTF) afforded an opportunity to measure the abundances and spatial distributions of coma volatiles in an Oort cloud comet at high spatial resolution near its close approach to Earth ($\Delta_\mathrm{min}\sim 0.28$ au on UT February 1). We conducted near-infrared spectroscopic observations of C/2022 E3 (ZTF) using iSHELL at the NASA Infrared Telescope Facility on UT 2023 February 9. Our measurements securely detected fluorescent emission from H$_2$O, CO, OCS, CH$_3$OH, CH$_4$, C$_2$H$_6$, C$_2$H$_2$, and HCN. For each instrumental setting we took exposures with the slit oriented parallel and also perpendicular to the projected Sun-comet vector, thereby enabling a test of the spatial distributions of these molecules. We report rotational temperatures, production rates, and abundance ratios (i.e., mixing ratios) for all sampled species. Our measurements found that molecular abundances in C/2022 E3 were depleted compared to their average values in Oort cloud comets with the exception of OCS, which was consistent. The H$_2$O production rate varied significantly and was likely tied to nucleus rotation effects. Measurements at the two slit orientations showed distinct column density and rotational temperature profiles for H$_2$O. Peak temperatures occurred off-nucleus and slower cooling was present in the anti-sunward hemisphere, consistent with the presence of icy grain sublimation in the coma.