Cometary Science Newsletter

March 2019
Michael S. P. Kelley (

Comet Interceptor mission proposal: Call for support

Comet Interceptor is a proposed mission to a dynamically new comet or an interstellar target, prepared in response to the European Space Agency (ESA) call for F-class missions. It is on a shortlist of six mission concepts invited to submit detailed proposals to ESA by March 20, 2019.

The mission would launch in 2028 with the ESA Ariel mission, and be 'parked' in a stable Sun-Earth L2 halo orbit for up to 2-3 years, until a suitable opportunity for a flyby mission to a dynamically new comet presents itself. Suitable targets will be comets whose orbits suggest that they are visiting the inner Solar System for the first time, including the possibility of interstellar objects like 'Oumuamua, that will have a perihelion closer than ~1.2 au and an ecliptic plane crossing time and location reachable with ~1.5 km/s delta-v from L2. Once a target is found, expected within a few years based on comet discovery rate predictions with the Large Synoptic Survey Telescope, the spacecraft will depart on an intercept trajectory. Before the flyby, the main spacecraft will deploy at least 2 sub-spacecraft, allowing separate, parallel paths through the coma and past the nucleus. This will provide 3D multispectral and polarimetric observations of the nucleus and coma, testing spatial coma inhomogeneity and the interaction with the solar wind on many scales. In addition to the targeting of a previously unvisited, much less evolved class of active comet, the unique multipoint measurements will complement single point observations from previous missions. Comet Interceptor is expected to include significant contributions from Japan and the USA.

Community support for the proposal is appreciated, especially before March 20, registered via the website

Team contact details are available on the website. Twitter handle: @cometintercept

Geraint Jones (UCL-MSSL, UK) & Colin Snodgrass (U. of Edinburgh, UK)

Refereed Articles

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

174P/Echeclus and Its Blue Coma Observed Post-outburst

  • Seccull, T. [1], Fraser, W. C. [1], Puzia, T. H. [2], Fitzsimmons, A. [1] and Cupani, G. 3
  1. Astrophysics Research Centre, Queen's University Belfast, University Road, Belfast, BT7 1NN UK
  2. Institute of Astrophysics, Pontificia Universidad Católica de Chile, Av. Vicuña Mackenna 4860, 7820436, Santiago, Chile
  3. INAF - Osservatorio Astronomico di Trieste via G. B. Tiepolo 11, I-34143, Trieste, Italy

It has been suggested that centaurs may lose their red surfaces and become bluer due to the onset of cometary activity, but the way in which cometary outbursts affect the surface composition and albedo of active centaurs is poorly understood. We obtained consistent visual-near-infrared (VNIR) reflectance spectra of the sporadically active centaur 174P/Echeclus during a period of inactivity in 2014 and six weeks after its outburst in 2016 to see if activity had observably changed the surface properties of the nucleus. We observed no change in the surface reflectance properties of Echeclus following the outburst compared to before, indicating that, in this case, any surface changes due to cometary activity were not sufficiently large to be observable from Earth. Our spectra and post-outburst imaging have revealed, however, that the remaining dust coma is not only blue compared to Echeclus, but also bluer than solar, with a spectral gradient of -7.7+/-0.6% per 0.1 micron measured through the 0.61-0.88 micron wavelength range that appears to continue up to a wavelength of around 1.3 micron before becoming neutral. We conclude that the blue visual color of the dust is likely not a scattering effect, and instead may be indicative of the dust's carbon-rich composition. Deposition of such blue, carbon-rich, comatic dust onto a red active centaur may be a mechanism by which its surface color could be neutralized.

The Astronomical Journal (Published)

DOI: 10.3847/1538-3881/aafbe4 arXiv: 1811.1122

Charge-Exchange Emission from Hydrogen-Like Carbon Ions Colliding with Water Molecules

  • Bodewits, D. 1
  • Hoekstra, R. 2,3
  1. Physics Department, Auburn University, Allison Laboratory, Auburn, AL 36849, USA
  2. Zernike Institute for Advanced Materials, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands
  3. Advanced Research Center for Nanolithography, Science Park 110, 1098 XG Amsterdam, The Netherlands

Absolute Extreme Ultraviolet emission cross-sections have been measured for collisions between C5+ and H2O in the range of 0.113 to 3.75 keV/amu (170–979 km/s). These results are used to derive velocity-dependent triplet-to-singlet ratios and emission cross-sections of the Cv K-series following single-electron capture. Comparison with existing measurements of integral charge-changing cross-sections indicates that auto-ionizing multi-electron capture is a significant reactions channel. This reaction may indirectly populate the n=2 states and thus add strength to the K α emission of Cv ions thereby co-determining the hardness ratio of K-series emission of Cv.

Atoms (Published)

DOI: 10.3390/atoms7010017

Organic Molecules in the Icy Bodies of Planetary Systems - Accepted Notions and New Ideas

  • Simonia, I.1
  • Cruikshank, D.P.2
  1. School of Natural Sciences and Engineering of Ilia State University, Georgia.
  2. Astrophysics Branch, NASA Ames Research Center, Moffett Field, CA, USA.

Cometary bodies are acknowledged to contain some of the most pristine matter in the Solar System, including ices and minerals. Certain number of previously unidentified spectral emission features detected in comets can be explained as emission by hydrocarbon molecules enclosed in a Shpolskii matrix and forming frozen hydrocarbon particles. UV-induced photoluminescence spectra of several self-organized molecules exhibit emission lines coincident with unidentified cometary lines, and open the possibility of the presence of this complex organic as components of the pristine organic inventory of comets. Complex organic was detected also in three satellites of Saturn. We describe in this paper results of our investigation of complex organic of the small bodies and present new approaches and hypotheses.

Open Astronomy (Published)

DOI: 10.1515/astro-2018-0038

Photoluminescence and Cathodoluminescence of the Solid Cometary Substance

  • Simonia, I. 1
  • Gucsik, A. [2], 3
  1. School of Natural Sciences and Engineering, Ilia State University, Georgia.
  2. Department of Geology, University of Johannesburg, Johannesburg, South Africa.
  3. Department of Nonlinear and Laser Optics, Wigner Research Institute for Physics, Hungarian Academy of Sciences, Budapest, Hungary.

We have proposed that solar ultraviolet and corpuscular radiations may excite photoluminescence and cathodoluminescence of the solid cometary substance including mineral halos of comets. Main characteristics of such possible luminescence and physical mechanisms of these phenomena have considered. Results of the tentative identification of previously unknown cometary emissions and data of laboratory research of meteorites are presented. We have shown as well that cometary solid substance may demonstrate red luminescence – similar of red luminescence by the circumstellar dust. Some other aspects of the problem have also been considered.

Open Astronomy (Published)

DOI: 10.1515/astro-2019-0003