Activities of the Comet Interceptor Comet Environment Working Group

Introduction: Comet Interceptor [1] is a joint space mission of the European Space Agency (ESA) and the Japan Aerospace Exploration Agency (JAXA). Its primary goals are to provide the first-ever in-situ characterisation of a Long Period Comet (LPC), which could be a dynamically-new comet or an interstellar object, and to perform the first simultaneous multi-point exploration of a cometary coma and nucleus.

Comet Interceptor is the first rapid response mission [2]. The mission will be launched in piggy back mode between the second semester of 2028 and the first semester of 2029 on Ariane 6, towards the Sun-Earth Lagrange point L2, where it will wait for its target comet passage.

Comet Interceptor consists of one main spacecraft (S/C A), and two deployable probes, named Probe B1 and Probe B2, which are provided by JAXA and ESA, respectively, allowing unique and simultaneous observations of the target from different geometries. The S/C A is devoted to the physical characterisation of the cometary nucleus and coma via remote sensing and in situ observations during the selected target fly-by.

Science Objectives: The mission will investigate the processes of planetesimal formation and disentangle primordial versus evolutionary processes by comparing the composition and physical properties of a pristine LPC with those of the Short Period Comets (SPCs) previously investigated by space missions, in particular by the Rosetta mission which explored comet 67P for more than two years. Specifically, the objectives of Comet Interceptor are:

1) Comet Nucleus Science: What is the surface composition, shape, morphology, and structure of the target object?

2) Comet Environment Science: What is the composition of the coma, its connection to the nucleus (activity) and the nature of its interaction with the solar wind?

Science Activities: The search for the target comet is underway, and preparations are being made for the scientific exploitation of the data from the mission’s three spacecraft.

The selection and scientific investigations of the target comet, as well as the development of the mission instruments and science operation areas, are supported by Working Groups (WGs). These are the Science Operation WG, Target Identification WG, and Comet Environment WG. The latter comprises three sub-WGs, covering the Comet Nucleus, Near-Environment (inner dust and gas coma), and Far-Environment (outer dust and gas coma and tails) topics. The specific tasks of the Comet Environment WG are to develop and provide results from scientific models addressing questions relevant to the implementation and operation of the mission and to achieve its scientific objectives.

Here, we provide a brief overview of the mission, and we present and describe the aims and activities of the working groups over the past year. One of the recent activities of all the Comet Environment sub-working groups is the preparation of a large repository of numerical models to favour the successful planning for scientific operations and data interpretation. Other activities include the analysis of available data on comets to better understand the environment expected during the encounter and establish base line parameters for target selection.

A list of virtual LPC targets has been established and these targets are under evaluation. Additional LPCs are expected to be detected in the near future thanks to ground-based survey, notably from the Vera C. Rubin Observatory Legacy Survey of Space and Time (LSST) [3]. These are going to be considered as proxy to inquire on the:

• 1) Nucleus science: (i) measure the size, shape, and rotation rate of the target comet nucleus; (ii) return resolved images of the surface that reveal its morphology: (iii) constrain the nucleus composition directly via remote sensing observations (imaging, spectroscopy, and polarimetry).
• 2) Environment science: (i) map the bulk neutral composition of the coma and determine any local structure and connection to the nucleus ices distributions and active areas; (ii) derive coma isotopic composition by mapping the distribution of neutral gasses and their relation to nucleus inhomogeneity; (iii) characterise the structure of the coma dust environment and determine any connection to the nucleus; (iv) characterise coma dust properties, and determine dust fluxes; (v) analyse motion and evolution of ion rays and other coma and tail features (i.e., dust and gas); (vi) characterise the plasma environment around the target, determine any resulting boundaries and assess energy, mass, and momentum transfer.

 

References: [1] Jones, G.H. et al. (2024) Space Sci. Rev. 220, 9. [2] Snodgrass, C. & Jones, G.H. (2019) Nat. Comm. 10, 5418. [3] Inno, L., et al. (2025) Icarus 429, 116443.