Cometary Science Newsletter

September 2021
Michael S. P. Kelley (

ESA Research Fellowships in Space Science

We are pleased to inform you about the opening of the call for European Space Agency's Research Fellowships in Space Science. The call is opening on 30 August 2021 with an application deadline on 27 September 2021.

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 a unique insight 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).

Duration: 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.

Eligibility: Citizens of ESA Member States or of cooperating and associated countries.

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

Deadline for applications is 27 September 2021.

Graduate-level position in Cometary Radiative Transfer Modeling

Opening for a junior researcher working on radiative transfer and spectral analysis of comets in the Astrochemistry Theory and Observation Group at NASA Goddard Space Flight Center.

Primary duties will involve C programming to enhance the functionality of our analysis software for studying cometary comae at radio (millimeter/submillimeter) wavelengths. The successful applicant will be responsible for maintaining and improving our radiative transfer code, working towards a public release on GitHub. Duties will include (1) being responsible for updating the electron collision methodology, (2) working on optimal parameter estimation methods, (3) testing, benchmarking and improving the code, and (4) using the code to perform analysis of ALMA observations of comets.

Necessary qualifications:

  1. Degree in Physics (or closely related discipline), including mathematics and quantum mechanics.
  2. Experience coding in C, C++, Java (or a closely related language).
  3. Ability to work independently, including troubleshooting, identifying and fixing bugs, writing code and constructing numerical algorithms.
  4. Familiarity with Unix-like operating system(s), and working with the terminal.
  5. Must have a strong desire to participate in cutting-edge astronomical research.
  6. Must be eligible to work in the USA.

Desirable qualifications (not critical for selection):

  1. Knowledge of observational astronomy (and spectroscopy).
  2. Prior exposure to physical science research literature.
  3. Experience working on novel/independent research projects.
  4. Experience with software development and version management using the git protocol.
  5. Familiarity with model fitting and optimal estimation.

Please apply by sending your resume, transcript and cover letter (including a summary of your qualifications and a statement of career goals), and arrange for a letter of reference to be sent to Application period will remain open until September 31st (or until filled).

Refereed Articles

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

Nondetection of Water-ice Grains in the Coma of Comet 46P/Wirtanen and Implications for Hyperactivity

  • Silvia Protopapa 1
  • Michael S. P. Kelley 2
  • Charles E. Woodward 3
  • Bin Yang 4, 5
  1. Southwest Research Institute, 1050 Walnut Street, Suite 300, Boulder, CO 80302, USA
  2. Department of Astronomy, University of Maryland, College Park, MD 20742, USA
  3. Minnesota Institute for Astrophysics, University of Minnesota, Minneapolis, MN 55455, USA
  4. European Southern Observatory, Alonso de Còrdova 3107, Vitacura, Casilla 19001, Santiago, Chile
  5. Núcleo de Astronomía, Facultad de Ingeniería y Ciencias, Universidad Diego Portales, Chile

Hyperactive comets have high water production rates, with inferred sublimation areas of order the surface area of the nucleus. Comets 46P/Wirtanen and 103P/Hartley 2 are two examples of this cometary class. Based on observations of comet Hartley 2 by the Deep Impact spacecraft, hyperactivity appears to be caused by the ejection of water-ice grains and/or water-ice rich chunks of nucleus into the coma. These materials increase the sublimating surface area, and yield high water production rates. The historic close approach of comet Wirtanen to Earth in 2018 afforded an opportunity to test Hartley 2 style hyperactivity in a second Jupiter-family comet. We present high spatial resolution, near-infrared spectroscopy of the inner coma of Wirtanen. No evidence for the 1.5- or 2.0-μm water-ice absorption bands is found in six 0.8-2.5 μm spectra taken around perihelion and closest approach to Earth. In addition, the strong 3.0-μm water-ice absorption band is absent in a 2.0-5.3 μm spectrum taken near perihelion. Using spectroscopic and sublimation lifetime models we set constraints on the physical properties of the ice grains in the coma, assuming they are responsible for the comet's hyperactivity. We rule out pure water-ice grains of any size, given their long lifetime. Instead, the hyperactivity of the nucleus and lack of water-ice absorption features in our spectra can be explained either by icy grains on the order of 1 μm in size with a small amount of low albedo dust (greater than 0.5% by volume), or large chunks containing significant amounts of water ice.

The Planetary Science Journal (Published)

DOI: 10.3847/PSJ/ac135a arXiv: 2107.01255