CO+CO₂ production rates of comets observed by NEOWISE

The Wide-field Infrared Survey Explorer (WISE) mission was launched in 2009 to survey the entire sky in the mid-infrared (3.4, 4.6, 12, and 22 μm). By October 2010, the primary and secondary cryogen tanks were depleted, making the 12 and 22 μm channel inoperable while the mission continued to collect data until February 2011, when the spacecraft was placed into hibernation. The spacecraft was then reactivated in October 2013, and re-named NEOWISE, with ongoing operation to this date. NEOWISE continues to survey the sky and as of mid-2020 has acquired over 945,000 confirmed infrared detection of approximately 36,500 different solar system objects.

In addition to the major goals of discovering and characterizing Near-Earth Objects (NEOs) WISE/NEOWISE was able to constrain the dust, the nucleus size and the carbon monoxide (CO) and carbon dioxide (CO₂) production in comets. The 4.6 μm channel allows observation of the strong cometary emission lines of CO (4.67 μm) and CO₂ (4.23 μm). CO and CO₂ are cometary ices that are more volatile than water ice; they are likely the main driver of the activity of comets at large heliocentric distances (Rh≳3 au). Deriving CO and CO₂ production rates of comets within 3 au is also extremely useful, considering that they are significant fractions of the total ice content in the comet. Even highly evolved comets can have a significant hypervolatile production. More generally, measuring the simultaneous gas and dust production, and the resulting dust-to-gas ratio, reveals fundamental properties of cometary activity and constrains cometary origin.

We will focus on approximately 60 comets observed by NEOWISE in 2014, 2015 and 2016 (NEOWISE - Year 1, 2, 3). We will present the dust production (Afρ) and CO+CO₂ production rates. We will investigate the relation between dust production and the gas production rate. We will analyze the relationships between dust production rate, gas production rate and heliocentric distance. Finally, we will compare result from short-period and long-periods comets. This work is a follow-up to Rosser et al. (2018) and Bauer et al. (2015), and we will build on some of the trends seen there.

1. Rosser et al. 2018, AJ 155, 164

2. Bauer et al. 2015, ApJ, 814, 85.