Cometary Science Newsletter

December 2021
Michael S. P. Kelley (

Refereed Articles

Abstracts of articles in press or recently published. Limited to 3000 characters.

Variable X-Ray Emission of Comet 46P/Wirtanen

  • Bonamente, E., 1
  • Christian, D. J., 2
  • Z.-X. Xing, 1,3
  • K. Venkataramani, 1
  • D. Koutroumpa, 4
  • D. Bodewits 1
  1. Auburn University, USA
  2. California State University Northridge, USA
  3. Hong Kong University, Hong Kong SAR, People's Republic of China
  4. LATMOS/IPSL, CNRS, France

In this paper, we present an analysis of X-ray and optical/ultraviolet (UV) data from the favorable (D ∼ 0.077 au) 2018 apparition of comet 46P/Wirtanen. The comet was observed during three different epochs (before, during, and after perihelion) over a 1.5 month period using the X-Ray Telescope (XRT) and Ultraviolet and Optical Telescope (UVOT) instruments on board the Neil Gehrels Swift Observatory and the Advanced CCD Imaging Spectrometer (ACIS) on board the Chandra X-ray Observatory. We clearly detected the comet’s charge exchange-induced emission during the first two epochs (Fx = (11.2 ± 0.8) and (6.9 ± 0.5) × 10−13 erg cm−2 s−1, respectively), while only an upper limit on the flux could be placed for the third epoch (Fx < 1.38 × 10−13 erg cm−2 s−1). As such, 46P/Wirtanen is one of the least luminous comets to be detected in X-rays. X-ray emission from the charge exchange between solar wind ions and the neutrals in the coma were analyzed against the water-production rate (Swift/UVOT) and space weather measurements. Further analyses of the emission features show that the solar wind properties inferred from the observed X-ray spectrum are in good agreement with those measured by the Advanced Composition Explorer (ACE) and Solar and Heliospheric Observatory (SOHO) spacecraft, proving the approach is reliable for solar wind diagnostics. It is also found that, despite the variability of the comet’s properties (e.g., the water- production rate used as a neutrals density proxy), cometary X-ray emission is primarily modulated by the solar wind.

The Planetary Science Journal (Published)

DOI: 10.3847/PSJ/ac2aac

Atomic Iron and Nickel in the Coma of C/1996 B2 (Hyakutake): Production Rates, Emission Mechanisms, and Possible Parents

  • S. J. Bromley, 1
  • B. Neff, 2
  • S. D. Loch, 1
  • J. P. Marler, 2
  • J. Országh, 3
  • K. Venkataramani, 1
  • D. Bodewits 1
  1. Department of Physics, Auburn University, Leach Science Center, Auburn AL 36832, USA
  2. Department of Physics and Astronomy, Clemson University, Clemson, SC 29630, USA
  3. Department of Experimental Physics, Faculty of Mathematics, Physics and Informatics, Comenius University in Bratislava, Mlynská dolina F-2, 842 48 Bratislava; Slovak Republic

Two papers recently reported the detection of gaseous nickel and iron in the comae of over 20 comets from observations collected over two decades, including interstellar comet 2I/Borisov. To evaluate the state of the laboratory data in support of these identifications, we reanalyzed archived spectra of comet C/1996 B2 (Hyakutake), one of the nearest and brightest comets of the past century, using a combined experimental and computational approach. We developed a new, many-level fluorescence model that indicates that the fluorescence emissions of Fe I and Ni I vary greatly with heliocentric velocity. Combining this model with laboratory spectra of an Fe-Ni plasma, we identified 22 lines of Fe I and 14 lines of Ni I in the spectrum of Hyakutake. Using Haser models, we estimate the nickel and iron production rates as QNi = (2.6–4.1) × 10^22 s−1 and QFe = (0.4–2.8) × 10^23 s−1. From derived column densities, the Ni/Fe abundance ratio log10[Ni/Fe] = −0.15 ± 0.07 deviates significantly from solar abundance ratios, and it is consistent with the ratios observed in solar system comets. Possible production and emission mechanisms are analyzed in the context of existing laboratory measurements. Based on the observed spatial distributions, excellent fluorescence model agreement, and Ni/Fe ratio, our findings support an origin consisting of a short-lived unknown parent followed by fluorescence emission. Our models suggest that the strong heliocentric velocity dependence of the fluorescence efficiencies can provide a meaningful test of the physical process responsible for the Fe I and Ni I emission.

The Planetary Science Journal (Published)

DOI: 10.3847/PSJ/ac2dff arXiv: 2106.04701

Early Activity in Comet C/2014 UN271 Bernardinelli–Bernstein as Observed by TESS

  • Tony L. Farnham, 1
  • Michael S. P. Kelley, 1
  • James M. Bauer 1
  1. University of Maryland

We used long duration observations from the Transient Exoplanet Survey Satellite (TESS) to investigate the behavior of comet C/2014 UN271 Bernardinelli–Bernstein at large heliocentric distances. By combining data from sector 03 (976 30 minute exposures from 2018), and sectors 29 and 30 (3585 and 3410 10 minute exposures, respectively, from 2020), we produced deep coadded images of the comet. A comparison of these results with similarly processed images of inactive Kuiper Belt objects and asteroids reveals that the comet was already exhibiting coma at heliocentric distances 23.8 and 21.2 au, making this one of the most distant comets for which preperihelion activity has been directly detected. A simple syndyne analysis of asymmetries in the coma suggests that activity probably started several years prior to these observations, and likely arose from emission in roughly the sunward direction. The images were used to produce photometric lightcurves, though no rotational variability was detected. We used NEOWISE observations from 2020 November 26–28 to place an upper limit of 2 × 1028 molecules s−1 (3σ) on the CO production rate.

The Planetary Science Journal (Published)

DOI: 10.3847/PSJ/ac323d