Cometary Science Newsletter

A Look at Outbursts of Comet C/2014 UN271 (Bernardinelli–Bernstein) near 20 au

• Michael S. P. Kelley ¹
• Rosita Kokotanekova ^2,3
• Carrie E. Holt ¹
• Silvia Protopapa ⁴
• Dennis Bodewits⁵
• Matthew M. Knight ⁶
• Tim Lister ⁷
• Helen Usher ⁸
• Joseph Chatelain ⁷
• Edward Gomez ⁹
• Sarah Greenstreet ¹⁰
• Tony Angel ¹¹
• Ben Wooding ¹²

1. Department of Astronomy, University of Maryland, College Park, MD 20742-0001, USA
2. European Southern Observatory, Karl-Schwarzschild-Str 2, D-85748 Garching, Germany
3. Institute of Astronomy and National Astronomical Observatory, Bulgarian Academy of Sciences, 72 Tsarigradsko shose Boulevard, 1784 Sofia, Bulgaria
4. Southwest Research Institute, 1050 Walnut Street, Suite 300, Boulder, CO 80302, USA
5. Physics Department, Leach Science Center, Auburn University, Auburn, AL 36849, USA
6. Physics Department, United States Naval Academy, 572C Holloway Road, Annapolis, MD 21402, USA
7. Las Cumbres Observatory, 6740 Cortona Drive, Suite 102, Goleta, CA 93117, USA
8. The Open University, Walton Hall, Milton Keynes, MK7 6AA, UK
9. Las Cumbres Observatory, School of Physics and Astronomy, Cardiff University, Queens Buildings, The Parade, Cardiff CF24 3AA, UK
10. Department of Astronomy and the DIRAC Institute, University of Washington, 3910 15th Avenue NE, Seattle, WA 98195, USA
11. Harlingten Observatory, Observatorio Sierra Contraviesa, Cortijo El Cerezo, Torvizcon 18430, Granada, Spain
12. St Mary's Catholic Primary School, Llangewydd Road, Bridgend, Wales, CF31 4JW, UK

Cometary activity may be driven by ices with very low sublimation temperatures, such as carbon monoxide ice, which can sublimate at distances well beyond 20 au. This point is emphasized by the discovery of Oort cloud comet C/2014 UN271 (Bernardinelli-Bernstein), and its observed activity out to ∼26 au. Through observations of this comet's optical brightness and behavior, we can potentially discern the drivers of activity in the outer solar system. We present a study of the activity of comet Bernardinelli-Bernstein with broad-band optical photometry taken at 19–20 au from the Sun (2021 June to 2022 February) as part of the LCO Outbursting Objects Key (LOOK) Project. Our analysis shows that the comet's optical brightness during this period was initially dominated by cometary outbursts, stochastic events that ejected ∼10⁷ to ∼10⁸ kg of material on short (< 1 day) timescales. We present evidence for three such outbursts occurring in 2021 June and September. The nominal nuclear volumes excavated by these events are similar to the 10–100 m pit-shaped voids on the surfaces of short-period comet nuclei, as imaged by spacecraft. Two out of three Oort cloud comets observed at large pre-perihelion distances exhibit outburst behavior near 20 au, suggesting such events may be common in this population. In addition, quiescent CO-driven activity may account for the brightness of the comet in 2022 January to February, but that variations in the cometary active area (i.e., the amount of sublimating ice) with heliocentric distance are also possible.

The Astrophysical Journal Letters (Published)

DOI: 10.3847/2041-8213/ac7bec NASA ADS: 2022ApJ...933L..44K arXiv: 2206.14888