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Made available in DSpace on 2022-04-29T08:37:10Z (GMT). No. of bitstreams: 0 Previous issue date: 2021-11-10
Comet C/2014 UN271 (Bernardinelli-Bernstein), incoming from the Oort cloud, is remarkable in having the brightest (and presumably largest) nucleus of any well-measured comet and having been discovered at the heliocentric distance r h ≈ 29 au, farther than any Oort cloud comet. In this work, we describe the discovery process and observations and the properties that can be inferred from images recorded until the first reports of activity in 2021 June. The orbit has i = 95°, with a perihelion of 10.97 au to be reached in 2031 and a previous aphelion at 40,400 ± 260 au. Backward integration of the orbit under a standard Galactic tidal model and known stellar encounters suggests a perihelion of q ≈ 18 au on its previous perihelion passage 3.5 Myr ago; hence, the current data could be the first ever obtained of a comet that has not been inside Uranus's orbit in 4 Gyr. The photometric data show an unresolved nucleus with absolute magnitude H r = 8.0, colors that are typical of comet nuclei or Damocloids, and no secular trend as it traversed the range 34-23 au. For the r-band geometric albedo p r , this implies a diameter of km. There is strong evidence of brightness fluctuations at the ±0.2 mag level, but no rotation period can be discerned. A coma, nominally consistent with a stationary1/ρ surface brightness distribution, grew in scattering cross section at an exponential rate from A f ρ ≈ 1 to ≈150 m as the comet approached from 28 to 20 au. The activity rate is consistent with a very simple model of sublimation of a surface species in radiative equilibrium with the Sun. The inferred enthalpy of sublimation matches those of CO2 and NH3. More volatile species, such as N2, CH4, and CO, must be far less abundant on the sublimating surfaces.
Department of Physics and Astronomy University of Pennsylvania
School of Physics University of New South Wales
UNSW Data Science Hub University of New South Wales
Department of Physics and Astronomy University of Western Ontario, 1151 Richmond Street
Institute for Astronomy University of Hawaii, 2680 Woodlawn Drive
Laboratório Interinstitucional de E-Astronomia - LIneA, Rua Gal. José Cristino 77, RJ
Fermi National Accelerator Laboratory, P.O. Box 500
Instituto de Física Teórica Universidade Estadual Paulista
Instituto de Fisica Teorica UAM/CSIC Universidad Autonoma de Madrid
CNRS UMR 7095 Institut d'Astrophysique de Paris
Sorbonne Universités UPMC Univ Paris 06 UMR 7095 Institut d'Astrophysique de Paris
Department of Physics and Astronomy University College London, Gower Street
Kavli Institute for Particle Astrophysics and Cosmology Stanford University, P.O. Box 2450
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Center for Astrophysical Surveys National Center for Supercomputing Applications, 1205 West Clark Street
Department of Astronomy University of Illinois at Urbana-Champaign, 1002 West Green Street
Institut de Física d'Altes Energies (IFAE) Barcelona Institute of Science and Technology Campus UAB, Bellaterra
Physics Department 2320 Chamberlin Hall University of Wisconsin-Madison, 1150 University Avenue
Jodrell Bank Center for Astrophysics School of Physics and Astronomy University of Manchester, Oxford Road
University of Nottingham School of Physics and Astronomy
Astronomy Unit Department of Physics University of Trieste, via Tiepolo 11
INAF-Osservatorio Astronomico di Trieste, via G.B. Tiepolo 11
Institute for Fundamental Physics of the Universe, Via Beirut 2
Observatório Nacional, Rua Gal. José Cristino 77, RJ
Department of Physics University of Michigan
Hamburger Sternwarte Universitat Hamburg, Gojenbergsweg 112
Centro de Investigaciones Energéticas Medioambientales y Tecnológicas (CIEMAT)
Santa Cruz Institute for Particle Physics
Institute of Theoretical Astrophysics University of Oslo, P.O. Box 1029 Blindern
Kavli Institute for Cosmological Physics University of Chicago
Institut d'Estudis Espacials de Catalunya (IEEC)
Institute of Space Sciences (ICE CSIC) Campus UAB, Carrer de Can Magrans, s/n
Department of Astronomy University of Michigan
Faculty of Physics Ludwig-Maximilians-Universitat, Scheinerstr. 1
School of Mathematics and Physics University of Queensland
Center for Cosmology and Astro-Particle Physics Ohio State University
Department of Physics Ohio State University
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Australian Astronomical Optics Macquarie University
Lowell Observatory, 1400 Mars Hill Road
George P. and Cynthia Woods Mitchell Institute for Fundamental Physics and Astronomy Department of Physics and Astronomy Texas A and M University
Institució Catalana de Recerca i Estudis Avancats
Institute of Astronomy University of Cambridge, Madingley Road
Department of Astrophysical Sciences Princeton University Peyton Hall
Department of Physics and Astronomy Pevensey Building University of Sussex
School of Physics and Astronomy University of Southampton
Computer Science and Mathematics Division Oak Ridge National Laboratory
Department of Physics Stanford University 382 Via Pueblo Mall
Department of Physics Duke University
Max Planck Institute for Extraterrestrial Physics, Giessenbachstrasse
Universitats-Sternwarte Fakultat für Physik Ludwig-Maximilians Universitat München, Scheinerstr. 1
Cerro Tololo Inter-American Observatory NSF's National Optical-Infrared Astronomy Research Laboratory, Casilla 603
Instituto de Física Teórica Universidade Estadual Paulista
