First Detection of Molecular Activity in the Largest Known Oort Cloud Comet: ALMA Imaging of C/2014 UN271 (Bernardinelli-Bernstein) at 16.6 au from the Sun

Abstract

We report observations of comet C/2014 UN271 (Bernardinelli-Bernstein) carried out on UT 2024 March 8 and 17 at a heliocentric distance ($r_{\mathrm{H}}$) of 16.6 au using the Atacama Large Millimeter/Submillimeter Array (ALMA). The CO ($J$=2-1) line at 230 GHz was detected along with continuum emission from its dust coma and large ($\sim$140 km) nucleus, revealing the nature of the activity drivers and outgassing kinematics of the largest Oort cloud comet discovered to date. This work presents spectrally integrated flux maps, autocorrelation spectra, production rates, and parent scale lengths for CO and a stringent upper limit for the H${}_2$CO production rate. CO outgassing displayed multiple active jets which evolved from one epoch to the next. The continuum emission was compact and spatially unresolved, and is consistent with thermal emission from the large nucleus and a tentative detection of a dust coma. Complementary optical observations provided activity context for the ALMA epochs, indicating that UN271 underwent an outburst in late February before returning to a quiescent brightness in mid--late March. These results represent the first secure detection of molecular activity reported in the literature for C/2014 UN271 and highlight the dynamic nature of this distantly active small world.

Published in The Astrophysical Journal Letters

References in corpus (22)

• Astropy: A Community Python Package for Astronomy
• The Astropy Project: Building an inclusive, open-science project and status of the v2.0 core package
• The Astropy Project: Sustaining and Growing a Community-oriented Open-source Project and the Latest Major Release (v5.0) of the Core Package
• The SIMBAD astronomical database
• astroquery: An Astronomical Web-Querying Package in Python
• Real-time processing of the imaging data from the network of Las Cumbres Observatory Telescopes using BANZAI
• Herschel measurements of the D/H and 16O/18O ratios in water in the Oort-cloud comet C/2009 P1 (Garradd)
• Detecting Weak Spectral Lines in Interferometric Data through Matched Filtering
• Mapping the release of volatiles in the inner comae of comets C/2012 F6 (Lemmon) and C/2012 S1 (ISON) using the Atacama Large Millimeter/Submillimeter Array
• Interferometric imaging of the sulfur-bearing molecules H2S, SO and CS in comet C/1995 O1 (Hale-Bopp)
• 2014-2015 Multiple Outbursts of 15P/Finlay
• C/2014 UN271 (Bernardinelli-Bernstein): the nearly spherical cow of comets
• A SUBLIME 3D Model for Cometary Coma Emission: the Hypervolatile-Rich Comet C/2016 R2 (PanSTARRS)
• Gas Sources from the Coma and Nucleus of Comet 46P/Wirtanen Observed Using ALMA
• Interferometric mapping of the 3.3-mm continuum emission of comet 17P/Holmes after its 2007 outburst
• Size and albedo of the largest detected Oort-cloud object: comet C/2014 UN 271 (Bernardinelli-Bernstein)
• A LOOK at Outbursts of Comet C/2014 UN${}_{271}$ (Bernardinelli-Bernstein) Near 20 au
• Six Outbursts of Comet 46P/Wirtanen
• Hubble Space Telescope Detection of the Nucleus of Comet C/2014 UN${}_{271}$ (Bernardinelli-Bernstein)
• The influence of individual stars on the long-term dynamics of comets C/2014 UN271 and C/2017 K2
• Detection of Remnant Dust Cloud Associated with the 2007 Outburst of 17P/Holmes
• Planck CO revisited: Improved CO line emission maps from Planck space mission observations