UCLA

Active solar system small bodies are investigated from the presently operational NEOWISE space-based mission with follow-up from ground-based observatories. The latter include the Keck, JCMT, ATLAS, and C28 telescopes. The primary focus of this work is to quantify the gas and dust production rates of active bodies in the solar system in contemporaneous, if not closely-temporal observational arcs over different stages of their orbital evolution. Specifically, the quantification of the gaseous species carbon monoxide (CO) and carbon dioxide (CO2) as well as dust are performed. Few measurements of these gases exist in the scientific literature and quantifying CO2 is essentially impossible from the ground due to severe telluric contamination from Earth’s CO2-rich atmosphere. The small fraction (∼0.04%) of CO2 in Earth’s atmosphere is significant enough to ‘blind’ ground-based telescopes from determining whether or not potential detection(s) of CO2 are coming from these active bodies. Other follow-up results are presented regarding the characterization of activity in comets and asteroids which imply new processes are involved when compared to long-standing historical models such as Whipple (1950, 1951) in our understanding of why small bodies suddenly become active in the solar system and elsewhere. This study also investigates the long-term (multi-year) monitoring of the morphological evolution of these bodies that are ultimately subject to perhaps the major source of activity, being the influence of continual irradiation from the Sun.

Work in the last two decades (e.g., Ootsubo et al. 2012; Jewitt et al. 2015a; Bauer et al. 2015, 2017, 2021; Bouziani & Jewitt 2022) and this Dissertation demonstrates the importance of characterizing the influence of gas and dust in observed activity for these objects. With further investigations of activity in distant small bodies that began in the 1990s such as 29P/Schwassmann-Wachmann 1 (SW1) by Senay and Jewitt (1994) and continuing in 1997 when Comet C/1995 O1 (Hale-Bopp) came to perihelion, the scientific community became further aware of the major significance of CO’s role in activity observed in comets. A few decades later, in 2020, the emergence and discovery of comet C/2020 F3 (NEOWISE) was the most recent bright comet to become active at the naked eye level in the northern hemisphere. This has led to further investigation of the drivers of activity in solar system small bodies, and to more frequent observations of these objects by both the amateur and scientific communities alike. Should CO and CO2 be the culprits and ‘major suspects’, the work presented in this Dissertation posit that we must characterize the activity, especially at multiple stages in their evolutionary journey.

We use previous terminology and metrics such as Afρ as a proxy to quantify the dust production and describe the overall nature of ‘activity’ that has been commonplace in the literature first described by A’Hearn et al. (1984). Afρ has been used as a standard metric for measuring the dust production of active bodies with those being ∼1000 cm or more are thus considered to be ‘hyperactive’. In this Dissertation, the objects investigated have been found to be active at times and regions where previous models would indicate activity must be caused by a process other than the sublimation of water-ice. Further, the objects investigated in this study have Afρ as low as several hundred cm (minimum <277; C/2014 B1 (Schwartz) for UT 2016 November) and as high as several thousand cm (maximum 6370; C/2017 K2 (Pan-STARRS) for UT 2022 August). Gas production rates, denoted by Q in units of molecules per second (mol s^–1) have all been found between ∼10^27 and ∼10^29 mol s^–1, respectively, if one assumes the excess emission is attributed to either all CO or all CO2. Previous values of Q (specifically with regards to CO and/or CO2; e.g., QCO & QCO2) that exist in the literature for comets have found most to be on the order of ∼10^25 and ∼10^26 mol s^–1 with a few (rare) measurements of these species on the order of ∼10^27 to 10^28 mol s^–1 depending on the measurement technique used and the part of the electromagnetic spectrum where measurements have been performed.

This work presents a subset of the many NEOWISE observed comets with specific focus placed on the exceptionally active comets, C/2014 B1 (Schwartz), C/2017 K2 (Pan-STARRS), C/2010 U3 (Boattini), and 29P/Schwassmann-Wachmann 1 (SW1). Comets observed by NEOWISE typically first appear active at ∼5 or 6 astronomical units (au). Most objects beyond this distance evade detection by current software algorithms as they appear too faint (see Chapter 2). All objects studied here were found to be active at distances up to about double (e.g., ∼12 au for K2) the aforementioned detection distance of around 5 to 6 au. For this reason, K2 was studied from 2019 to 2022 as it was inbound. With SW1 being a short-period comet (SPC) with an atypical (∼circular) orbit residing in the near-vicinity of the outer solar system, it was possible to investigate over the years 2014 to 2022 using the same instrumentation and measurement techniques in Chapter 3. Moreover, all observational epochs are used where these objects appear in the co-added data that boost the signal-to-noise allowing for further analysis to be performed.