Cometary Science Newsletter

September 2023
Michael S. P. Kelley (

ESA Research Fellowships in Space Science

We are pleased to inform you about the opening of the call for the European Space Agency's Research Fellowships in Space Science. The call is opening on 28 August 2023 with an application deadline on 18 September 2023.

ESA's postdoctoral Research Fellowship programme offers early-career scientists and engineers the possibility to carry out research in a variety of disciplines related to space science, space applications or space technology. Research Fellowships in Space Science specifically offer the opportunity to contribute to ESA's endeavour to explore our Solar System and the Universe, and cover the fields of heliophysics, planetary science, astrophysics and fundamental physics.

The research fellowships offer unique insights into ESA's environment and activities while conducting cutting-edge research. Mentoring and training opportunities are available, as are possibilities to engage with ESA science-related activities (e.g., archive/data science, operations, calibration, communication, citizen science).

Within the Science Directorate (SCI), we welcome all independent proposals for innovative research associated with one or more of our missions. The Space Science fellowships can be taken up at any of the three sites ESAC (Spain), ESTEC (Netherlands) or STScI (USA) and we encourage applicants to choose sites that allow for best local collaborations.


Appointments are for a maximum of three years. The initial project is for two years. An extension for a third year requires a dedicated proposal and is frequently granted.

More information on the Research Fellowship programme and on how to apply can be found at

Refereed Articles

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

Low NH3/H2O ratio in comet C/2020 F3 (NEOWISE) at 0.7 au from the Sun

  • Drozdovskaya, M. N. 1
  • Bockelée-Morvan D. 2
  • Crovisier J. 2
  • McGuire B. A. 3, 4
  • Biver N. 2
  • Charnley S. B. 5
  • Cordiner M. A. 5, 6
  • Milam S. N. 5
  • Opitom C. 7
  • Remijan A. J. 4
  1. Center for Space and Habitability, UniversitätBern, Switzerland
  2. LESIA, Observatoire de Paris, Université PSL, Sorbonne Université, Université Paris Cité, CNRS, France
  3. Department of Chemistry, Massachusetts Institute of Technology, USA
  4. National Radio Astronomy Observatory, USA
  5. Astrochemistry Laboratory, NASA Goddard Space Flight Center, USA
  6. Department of Physics, Catholic University of America, USA
  7. Institute for Astronomy, University of Edinburgh, UK

A lower-than-solar elemental nitrogen content has been demonstrated for several comets, including 1P/Halley and 67P/C-G with independent in situ measurements of volatile and refractory budgets. The recently discovered semi-refractory ammonium salts in 67P/C-G are thought to be the missing nitrogen reservoir in comets. The thermal desorption of ammonium salts from cometary dust particles leads to their decomposition into ammonia and a corresponding acid. The NH3/H2O ratio is expected to increase with decreasing heliocentric distance with evidence for this in near-infrared observations. NH3 has been claimed to be more extended than expected for a nuclear source. Here, the aim is to constrain the NH3/H2O ratio in comet C/2020 F3 (NEOWISE) during its July 2020 passage. OH emission from comet C/2020 F3 (NEOWISE) was monitored for 2 months with NRT and observed from GBT on 24 July and 11 August 2020. Contemporaneously with the 24 July 2020 OH observations, the NH3 hyperfine lines were targeted with GBT. The concurrent GBT and NRT observations allowed the OH quenching radius to be determined at (5.96±0.10)×10^4 km on 24 July 2020, which is important for accurately deriving Q(OH). C/2020 F3 (NEOWISE) was a highly active comet with Q(H2O)≈2×10^30 molec s^-1 one day before perihelion. The 3σ upper limit for QNH3/QH2O is <0.29% at 0.7 au from the Sun. The obtained NH3/H2O ratio is a factor of a few lower than measurements for other comets at such heliocentric distances. The abundance of NH3 may vary strongly with time depending on the amount of water-poor dust in the coma. Lifted dust can be heated, fragmented, and super-heated; whereby, ammonium salts, if present, can rapidly thermally disintegrate and modify the NH3/H2O ratio.

Astronomy & Astrophysics (In press)

DOI: 10.1051/0004-6361/202346402 NASA ADS: 2023arXiv230711486D arXiv: 2307.11486

Gas Sources from the Coma and Nucleus of Comet 46P/Wirtanen Observed Using ALMA

  • M. A. Cordiner 1,2
  • N. X. Roth 1,2
  • S. N. Milam 1
  • G. L. Villanueva 3
  • D. Bockelée-Morvan 4
  • A. J. Remijan 5
  • S. B. Charnley 1
  • N. Biver 4
  • D. C. Lis 6
  • C. Qi 7
  • B. P. Bonev 8
  • J. Crovisier 4
  • and J. Boissier 9
  1. Astrochemistry Laboratory, NASA Goddard Space Flight Center, 8800 Greenbelt Road, Greenbelt, MD 20771, USA.
  2. Department of Physics, Catholic University of America, Washington, DC 20064, USA.
  3. Planetary Systems Laboratory, NASA Goddard Space Flight Center, 8800 Greenbelt Road, Greenbelt, MD 20771, USA.
  4. LESIA, Observatoire de Paris, Université PSL, CNRS, Sorbonne Université, Université de Paris, 5 place Jules Janssen, F-92195 Meudon, France.
  5. National Radio Astronomy Observatory, Charlottesville, VA 22903, USA.
  6. Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109, USA.
  7. Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, MS 42, Cambridge, MA 02138, USA.
  8. Department of Physics, American University, Washington, DC 20016, USA.
  9. Institut de Radioastronomie Millimetrique, 300 rue de la Piscine, F-38406, Saint Martin d'Heres, France.

Gas-phase molecules in cometary atmospheres (comae) originate primarily from (1) outgassing by the nucleus, (2) sublimation of icy grains in the near-nucleus coma, and (3) coma (photo)chemical processes. However, the majority of cometary gases observed at radio wavelengths have yet to be mapped, so their production/release mechanisms remain uncertain. Here we present observations of six molecular species toward comet 46P/Wirtanen, obtained using the Atacama Large Millimeter/submillimeter Array during the comet's unusually close (∼0.1 au) approach to Earth in 2018 December. Interferometric maps of HCN, CH3OH, CH3CN, H2CO, CS, and HNC were obtained at an unprecedented sky-projected spatial resolution of up to 25 km, enabling the nucleus and coma sources of these molecules to be accurately quantified. The HCN, CH3OH, and CH3CN spatial distributions are consistent with production by direct outgassing from (or very close to) the nucleus, with a significant proportion of the observed CH3OH originating from sublimation of icy grains in the near-nucleus coma (at a scale length Lp = 36 ± 7 km). On the other hand, H2CO, CS, and HNC originate primarily from distributed coma sources (with Lp values in the range 550–16,000 km), the identities of which remain to be established. The HCN, CH3OH, and HNC abundances in 46P are consistent with the average values previously observed in comets, whereas the H2CO, CH3CN, and CS abundances are relatively low.

The Astrophysical Journal (Published)

DOI: 10.3847/1538-4357/ace0bc NASA ADS: 2023ApJ...953...59C arXiv: 2305.04822

Cometary dust collected by MIDAS on board Rosetta. II. Particle shape descriptors and pristineness evaluation

  • M. Kim 1,2,3
  • T. Mannel 1
  • J. Lasue 4
  • A. Longobardo 5
  • M. S. Bentley 6
  • R. Moissl 7
  • and the MIDAS team
  1. Space Research Institute of the Austrian Academy of Sciences, Austria
  2. Department of Physics, University of Warwick, UK
  3. Centre for Exoplanets and Habitability, University of Warwick, UK
  4. Université de Toulouse, CNRS, France
  5. Istituto Nazionale di Astrofisica, Istituto di Astrofisica e Planetologia Spaziali, Italy
  6. European Space Astronomy Centre, Spain
  7. Scientific Support Office, European Space Research and Technology Centre, The Netherlands

The MIDAS (Micro-Imaging Dust Analysis System) atomic force microscope on board the Rosetta comet orbiter investigated and measured the 3D topography of a few hundred nm to tens of μm sized dust particles of 67P/Churyumov-Gerasimenko with resolutions down to a few nanometers, giving insights into the physical processes of our early Solar System. We analyze the shapes of the cometary dust particles collected by MIDAS on the basis of a recently updated particle catalog with the aim to determine which structural properties remained pristine. We develop a set of shape descriptors and metrics such as aspect ratio, elongation, circularity, convexity, and particle surface/volume distribution, which can be used to describe the distribution of particle shapes. Furthermore, we compare the structure of the MIDAS dust particles and the clusters in which the particles were deposited to those found in previous laboratory experiments and by Rosetta/COSIMA. Finally, we combine our findings to calculate a pristineness score for MIDAS particles and determine the most pristine particles and their properties. We find that the morphological properties of all cometary dust particles at the micrometer scale are surprisingly homogeneous despite originating from diverse cometary environments (e.g., different collection targets that are associated with cometary activities/source regions and collection velocities/periods). We next find that the types of clusters found by MIDAS show good agreement with those defined by previous laboratory experiments, however, there are some differences to those found by Rosetta/COSIMA. Based on our result, we rate 19 out of 1082 MIDAS particles at least moderately pristine, i.e., they are not substantially flattened by impact, not fragmented, and/or not part of a fragmentation cluster.

Appendix table is only available in electronic form at the CDS via anonymous ftp to ( or via

All MIDAS dust coverage, clustering, and shape descriptor maps can be found at

Astronomy & Astrophysics (In press)

DOI: 10.1051/0004-6361/202347173 NASA ADS: 2023arXiv230805875K arXiv: 2308.05875