Understanding cometary volatiles and asteroid evolution with ultraviolet observations and new techniques

Abstract

Comets and asteroids are believed to be remnants of the planet formation process and are critical for understanding the history of our solar system, the origins of life, and offer the potential for space mining. Despite the importance of these small bodies, current knowledge about them is mainly based on remote observations that can only provide information about their surfaces or comae. To fully understand their nature and history, it is essential to characterize the volatiles and surfaces of these bodies and link them to their bulk properties. The ultraviolet (UV) waveband has been proven to be highly effective in understanding the volatiles and surfaces of comets and asteroids through both observations and experiments. UV emissions from gas radical species in comets provide valuable insights into the chemical and physical processes in the coma and the surrounding interplanetary environment. Similarly, the UV waveband is more sensitive to certain effects and elements, such as space weathering and iron content (Fe3+), in asteroids than longer wavelengths. However, the number of UV observations is significantly limited by the strong atmospheric extinction on Earth and the low UV brightness of comets and asteroids. Therefore, the goal of this work is to improve understanding of cometary volatiles and asteroid surface evolution by conducting new UV observations and analyzing archived ones using the Ultraviolet and Optical Telescope (UVOT) on board the Neil Gehrels Swift Observatory (Swift). Moreover, Specialized observation strategies and advanced data preparation and processing techniques were developed for small bodies that appear extended or smeared due to coma and apparent motion, in order to obtain more accurate and detailed information about comets and asteroids. We applied these techniques to three observation campaigns. The first campaign involved detecting activities of the first clearly active interstellar comet 2I/Borisov, where we found its water production rates increased steadily before perihelion but decreased rapidly after perihelion. We also found an active fraction of at least 55% of the surface, and confirmed that 2I/Borisov is carbon-chain depleted and enriched in NH2 relative to water. The second campaign involved the simultaneous imaging and spectroscopy of the largest outbursts of the comet 29P/Schwassmann-Wachmann 1. We detected two expanding and darkening outflow structures, which may indicate two or more active areas on the nucleus. No gas emission was detected, and the dust colors need to be further examined. Finally, we analyzed spectra measured for 18 asteroids, which were generally consistent with spectra observed by other instruments and filled spectral gaps important for measuring space weathering. However, further examination is needed to check the close relations found between taxonomic classes and spectral shapes.