Cometary Science Newsletter

September 2022
Michael S. P. Kelley (

ESA Research Fellowships in Space Science

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 19 September 2022.

Refereed Articles

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

Destruction of Long-Period Comets

  • Jewitt, D 1
  1. UCLA

We identify a sample of 27 long-period comets for which both non-gravitational accelerations and Lyman-alpha based gas production rates are available. Seven of the 27 comets (i.e. about 25 percent) did not survive perihelion because of nucleus fragmentation or complete disintegration. Empirically, the latter nuclei have the smallest gas production rates and the largest non-gravitational accelerations, which are both indicators of small size. Specifically, the disintegrating nuclei have a median radius of only 0.41 km, one quarter of the 1.60 km median radius of those surviving perihelion. The disintegrating comets also have a smaller median perihelion distance (0.48 au) than do the survivors (0.99 au). We compare the order of magnitude timescale for outgassing torques to change the nucleus spin, t1, with the time spent by each comet in strong sublimation, t2, finding that the disrupted comets are those with t1 < t2. The destruction of near-Sun long-period comets is thus naturally explained as a consequence of rotational break-up. We discuss this process as a contributor to Oort's long mysterious “fading parameter.”

The Astronomical Journal (In press)

arXiv: 2208.04469

Identification and characterization of a new ensemble of cometary organic molecules

  • Hänni, N. 1
  • Altwegg, K. 1
  • Combi, M. 2
  • Fuselier, S. A. 3,4
  • De Keyser, J. 5
  • Rubin, M. 1
  • Wampfler, S. F. 6
  1. Physics Institute, Space Research & Planetary Sciences, University of Bern, Sidlerstrasse 5, 3012 Bern, Switzerland.
  2. Department of Climate and Space Sciences and Engineering, University ofMichigan, Ann Arbor, MI, USA.
  3. Space Science Directorate, Southwest Research Institute, San Antonio, TX, USA.
  4. Department of Physics and Astronomy, The University of Texas at San Antonio, San Antonio, TX, USA.
  5. Royal Belgian Institute for Space Aeronomy, BIRA-IASB, Brussels, Belgium.
  6. Center for Space and Habitability, University of Bern, Gesellschaftsstrasse 6, 3012 Bern, Switzerland.

In-situ study of comet 1P/Halley during its 1986 apparition revealed a surprising abundance of organic coma species. It remained unclear, whether or not these species originated from polymeric matter. Now, high-resolution mass-spectrometric data collected at comet 67P/Churyumov-Gerasimenko by ESA’s Rosetta mission unveil the chemical structure of complex cometary organics. Here, we identify an ensemble of individual molecules with masses up to 140 Da while demonstrating inconsistency of the data with relevant amounts of polymeric matter. The ensemble has an average composition of C1H1.56O0.134N0.046S0.017, identical to meteoritic soluble organic matter, and includes a plethora of chain-based, cyclic, and aromatic hydrocarbons at an approximate ratio of 6:3:1. Its compositional and structural properties, except for the H/C ratio, resemble those of other Solar System reservoirs of organics—from organic material in the Saturnian ring rain to meteoritic soluble and insoluble organic matter—, which is compatible with a shared prestellar history.

Nature Communications (Published)

DOI: 10.1038/s41467-022-31346-9

Sublimation Origin of Active Asteroid P/2018 P3

  • Yoonyoung Kim 1
  • Jessica Agarwal 1,2
  • David Jewitt 3
  • Max Mutchler 4
  • Stephen Larson 5
  • Harold Weaver 6
  • Michael Mommert 7
  1. Institute for Geophysics and Extraterrestrial Physics, TU Braunschweig, Germany
  2. Max Planck Institute for Solar System Research, Germany
  3. Department of Earth, Planetary and Space Sciences, UCLA, USA
  4. Space Telescope Science Institute, USA
  5. Lunar and Planetary Laboratory, University of Arizona, USA
  6. Johns Hopkins University Applied Physics Laboratory, USA
  7. University of St. Gallen, Switzerland

Active asteroids show (typically transient) cometary activity, driven by a range of processes. A sub-set, sometimes called main-belt comets, may be driven by sublimation and so could be useful for tracing the present-day distribution of asteroid ice. Object P/2018 P3 has a Tisserand parameter 3.096 but a high eccentricity 0.415, placing it within the dynamical boundary between asteroids and comets. We aim to determine the cause of activity (sublimation or something else) and assess the dynamical stability of P3, in order to better constrain the intrinsic ice content in the main belt. We obtained Hubble Space Telescope images of P3 at the highest angular resolution. We compared the observations with a Monte Carlo model of dust dynamics. We identified and analyzed archival CFHT (2013) and NEOWISE (2018) data. In addition, we numerically integrated the orbits of P3 clones for 100 Myr. P3 has been recurrently active near two successive perihelia (at 1.76 AU), indicative of a sublimation origin. The absence of 4.6 um band excess indicates zero or negligible CO or CO2 gas production from P3. The properties of the ejected dust are remarkably consistent with those found in other main-belt comets (continuous emission of ~0.05-5 mm particles at 0.3-3 m/s speeds), with mass-loss rates of >~2 kg/s. The orbit of P3 is unstable on timescales ~10 Myr. We speculate that P3 has recently arrived from a more stable source (either the Kuiper Belt or elsewhere in the main belt) and has been physically aged at its current location, finally becoming indistinguishable from a weakly sublimating asteroid in terms of its dust properties. Whatever the source of P3, given the dynamical instability of its current orbit, P3 should not be used to trace the native distribution of asteroid ice.

Astronomy & Astrophysics (In press)

arXiv: 2208.07868