Cometary Science Newsletter

March 2023
Michael S. P. Kelley (

Postdoctoral Research Opportunity on Small Bodies

The State Key Laboratory of Lunar and Planetary Science at Macau University of Science and Technology, Macau SAR, China ( now welcomes applications for a postdoctoral research position working with Dr. Man-To Hui to study the physical and dynamical properties of asteroids and comets (including interstellar objects and other relevant objects/topics). Applicants with experience in data reduction/analysis of astronomical observations and/or numerical simulations of orbital dynamics/thermodynamics will be prioritised. The position has a two-year term, starting as early as possible in 2023. Depending on the funding availability, an extension of the position is possible. The salary will be 25,000 MOP per month, and there will be additional support for publication charges and conference trips. Prospective applicants should obtain a Ph.D. degree in astronomy, planetary sciences, or other relevant fields, with proof of research competence and enthusiasm, such as a strong record of publication. The successful applicant will be encouraged to pursue independent research. Besides research, the applicant may enjoy themselves by exploring Macau, a unique place in the world where Chinese and Portuguese cultures met and mixed, and may even win extra money in casinos.

To apply for the position, the applicant should submit a cover letter, CV, research statement, and contact details of two referees who will write a recommendation to Dr. Man-To Hui at by 30 April 2023 for full consideration. Should you have more questions, feel free to contact Dr. Man-To Hui.

ESA Archival Research Visitor Programme

To increase the scientific return from its space science missions, the European Space Agency (ESA) welcomes applications from scientists interested in pursuing research projects based on data publicly available in the ESA Space Science Archives (

The ESA Archival Research Visitor Programme is open to scientists, at all career levels, affiliated with institutes in ESA Member States and Collaborating States. Early-career scientists (within 10 years of the PhD) are particularly encouraged to apply. Applications by PhD students are also welcome.

During their stay, visiting scientists will have access to archives and mission specialists for help with the retrieval, calibration, and analysis of archival data. In principle, all areas of space research covered by ESA science missions can be supported.

Residence lasts typically between one and three months, also distributed over multiple visits. Research projects can be carried out at ESAC (Madrid, Spain) and at ESTEC (Noordwijk, Netherlands). To offset the expenses incurred by visitors, ESA covers travel costs from and to the home institution and provides support for lodging expenses and meals.

Applications received before 1 May 2023 will be considered for visits in autumn 2023 and winter 2024.

For further details, including areas of research and contact information, please refer to:

or write to the programme coordinators at

Refereed Articles

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

On Averaging Eccentric Orbits: Implications for the Long-term Thermal Evolution of Comets

  • Gkotsinas, A. 1
  • Guilbert-Lepoutre, A. 1
  • Raymond, S. N. 2
  1. CNRS - University of Lyon, LGLTPE, France
  2. CNRS - University of Bordeaux, LAB, France

One of the common approximations in long-term evolution studies of small bodies is the use of circular orbits averaging the actual eccentric ones, facilitating the coupling of processes with very different timescales, such as the orbital changes and the thermal processing. Here we test a number of averaging schemes for elliptic orbits in the context of the long-term evolution of comets, aiming to identify the one that best reproduces the elliptic orbits’ heating patterns and the surface and subsurface temperature distributions. We use a simplified thermal evolution model applied on simulated comets both on elliptic and on their equivalent averaged circular orbits, in a range of orbital parameter space relevant to the inner solar system. We find that time-averaging schemes are more adequate than spatial-averaging ones. Circular orbits created by means of a time average of the equilibrium temperature approximate efficiently the subsurface temperature distributions of elliptic orbits in a large area of the orbital parameter space, rendering them a powerful tool for averaging elliptic orbits.

The Astronomical Journal (Published)

DOI: 10.3847/1538-3881/acaafd NASA ADS: 2023AJ....165...67G arXiv: 2212.06638

The Gateway from Centaurs to Jupiter-family Comets: Thermal and Dynamical Evolution

  • Guilbert-Lepoutre, A. 1
  • Gkotsinas, A. 1
  • Raymond, S. N. 2
  • Nesvorny, D. 3
  1. CNRS - University of Lyon, LGLTPE, France
  2. CNRS - University of Bordeaux, LAB, France
  3. Department of Space Studies, Southwest Research Institute, USA

It was recently proposed that there exists a “gateway” in the orbital parameter space through which Centaurs transition to Jupiter-family comets (JFCs). Further studies have implied that the majority of objects that eventually evolve into JFCs should leave the Centaur population through this gateway. This may be naively interpreted as gateway Centaurs being pristine progenitors of JFCs. This is the point we want to address in this work. We show that the opposite is true: gateway Centaurs are, on average, more thermally processed than the rest of the population of Centaurs crossing Jupiter’s orbit. Using a dynamically validated JFC population, we find that only ∼20% of Centaurs pass through the gateway prior to becoming JFCs, in accordance with previous studies. We show that more than half of JFC dynamical clones entering the gateway for the first time have already been JFCs— they simply avoided the gateway on their first pass into the inner solar system. By coupling a thermal evolution model to the orbital evolution of JFC dynamical clones, we find a higher than 50% chance that the layer currently contributing to the observed activity of gateway objects has been physically and chemically altered, due to previously sustained thermal processing. We further illustrate this effect by examining dynamical clones that match the present-day orbits of 29P/Schwassmann-Wachmann 1, P/2019 LD2 (ATLAS), and P/2008 CL94 (Lemmon).

The Astrophysical Journal (Published)

DOI: 10.3847/1538-4357/acaa3a NASA ADS: 2023ApJ...942...92G arXiv: 2212.06637

Fragment Dynamics in Active Asteroid 331P/Gibbs

  • Man-To Hui 1
  • David Jewitt 2
  1. Macau University of Science and Technology, Macau
  2. UCLA, USA

We present a dynamical analysis of the fragmented active asteroid 331P/Gibbs. Using archival images taken by the Hubble Space Telescope from 2015 to 2018, we measured the astrometry of the primary and the three brightest (presumably the largest) components. Conventional orbit determination revealed a high degree of orbital similarity between the components. We then applied a fragmentation model to fit the astrometry, obtaining key parameters including the fragmentation epochs and separation velocities. Our best-fit models show that Fragment B separated from the primary body at a speed of ~1 cm s-1 between 2011 April and May, whereas two plausible scenarios were identified for Fragments A and C. The former split either from the primary or from Fragment B, in 2011 mid June at a speed of ~8 cm s-1, and the latter split from Fragment B either in late 2011 or between late 2013 and early 2014, at a speed of ~0.7-0.8 cm s-1. The results are consistent with rotational disruption as the mechanism causing the cascading fragmentation of the asteroid, as suggested by the rapid rotation of the primary. The fragments constitute the youngest known asteroid cluster, providing us with a great opportunity to study asteroid fragmentation and formation of asteroid clusters.

The Astronomical Journal (Published)

DOI: 10.3847/1538-3881/ac978d NASA ADS: 2022AJ....164..236H arXiv: 2210.01432

Comet 108P/Ciffreo: The Blob

  • Kim, Y. 1
  • Jewitt, D. 2
  • Luu, J. 3
  • Li, J. 2
  • Mutchler, M. 4
  1. TU Braunschweig
  2. UCLA
  3. University of Oslo
  4. STScI

Short-period comet 108P/Ciffreo is known for its peculiar double morphology, in which the nucleus is accompanied by a co-moving, detached, diffuse 'blob'. We report new observations of 108P/Ciffreo taken with the Hubble Space Telescope and the Nordic Optical Telescope and use them to determine the cause of this unusual morphology. The separation and the longevity of the blob across several orbits together rule out the possibility of a single, slow-moving secondary object near the primary nucleus. We use a model of coma particle dynamics under the action of solar gravity and radiation pressure to show that the blob is an artifact of the turn-around of particles ejected sunward and repelled by sunlight. Numerical experiments limit the range of directions which can reproduce the morphology and explain why the co-moving blob appearance is rare.

The Astronomical Journal (In press)

arXiv: 2302.03697

Perihelion Activity of (3200) Phaethon is Not Dusty: Evidence from STEREO/COR2 Observations

  • Man-To Hui 1
  1. Macau University of Science and Technology

We present an analysis of asteroid (3200) Phaethon using coronagraphic observations from 2008 to 2022 by the COR2 cameras onboard the twin Solar TErrestrial RElations Observatory spacecraft. Although undetected in individual images, Phaethon was visible in stacks combined from the same perihelion observations, yet only at small (≲30°) but not large (≳150°) phase angles. The observations are in line with the contribution from a bare nucleus, thereby seriously contradicting the interpretation based on HI-1 observations that attributes the perihelion activity to the ejection of μm-sized dust. We obtained an upper limit to the effective cross section of μm-sized dust to be ≲105 m2, at least three orders of magnitude smaller than earlier estimates based on HI-1 data. On the contrary, the COR2 observations cannot rule out the existence of mm-sized or larger debris around Phaethon. However, the fact that no postperihelion debris tail has ever been detected for Phaethon suggests the unimportance of such dust in the perihelion activity. We thus conclude that the perihelion activity of Phaethon is highly unlikely relevant to the ejection of dust. Rather, we deduce that the activity is associated with gas emissions, possibly Fe I and/or Na D lines. To verify our conjecture and to fully understand the perihelion activity of Phaethon, more observations at small heliocentric distances are desired. We compile a list of observing windows ideal for the search of gas emissions of the asteroid from ground telescopes. The best opportunities will be during total solar eclipses.

The Astronomical Journal (Published)

DOI: 10.3847/1538-3881/acae9c NASA ADS: 2023AJ....165...94H arXiv: 2206.09704