Determining the dust environment of an unknown comet for a spacecraft flyby: The case of ESA’s Comet Interceptor mission^★

¹ CNRS, Observatoire de la Côte d’Azur, Laboratoire J.-L. Lagrange, CS 34229, 06304 Nice Cedex 4, France
e-mail: raphael.marschall@spacemarschall.net
² Southwest Research Institute, 1050 Walnut St, Suite 300, Boulder, CO 80302, USA
³ INAF – Istituto di Astrofísica e Planetologia Spaziali, Area Ricerca Tor Vergata, Via Fosso del Cavaliere 100, 00133 Rome, Italy
⁴ LESIA, Observatoire de Paris, Université PSL, CNRS, Sorbonne Université, Université de Paris, 5 Place Jules Janssen, 92195 Meudon, France
⁵ Department of Astronomy, University of Maryland, College Park, MD 20742-0001, USA
⁶ European Space Research and Technology Centre (ESTEC), European Space Agency (ESA), Keplerlaan 1, 2201-AZ Noordwijk, The Netherlands
⁷ Institute for Astronomy, University of Edinburgh, Royal Observatory, Edinburgh EH9 3HJ, UK
⁸ Mullard Space Science Laboratory, University College London, Holmbury St. Mary, Dorking, Surrey RH5 6NT, UK
⁹ The Centre for Planetary Sciences at UCL/Birkbeck, London WC1E 6BT, UK
¹⁰ INAF – Osservatorio Astronomico di Trieste, Italy
¹¹ Institute of Geological Sciences, Freie Universität Berlin, Germany
¹² DLR Institute of Planetary Research, Germany
¹³ Instituto de Astrofísica de Andalucia, CSIC. Glorieta de la Astronomia sn. Granada 18008, Spain
¹⁴ Department of Physics and Astronomy, University of Padova, vicolo Osservatorio 3, Padova, Italy
¹⁵ LATMOS, Sorbonne Univ., CNRS, Campus Pierre et Marie Curie, BC 102 4 place Jussieu, 75005 Paris, France

Received: 26 March 2022
Accepted: 1 August 2022

Abstract

Context. An assessment of the dust environment of a comet is needed for data analysis and planning spacecraft missions, such as ESA’s Comet Interceptor (CI) mission. The distinctive feature of CI is that the target object will be defined shortly before (or even after) launch; as a result, the properties of the nucleus and dust environment are poorly constrained, and therefore make the assessment of the dust environment challenging.

Aims. The main goal of the work is to provide realistic estimations of a dust environment based on very general parameters of possible target objects.

Methods. Contemporary numerical models of a dusty-gas coma were used to obtain spatial distribution of dust for a given set of parameters. By varying parameters within a range of possible values, we obtained an ensemble of possible dust distributions. Then, this ensemble was statistically evaluated in order to define the most probable cases and hence reduce the dispersion. This ensemble can not only be used to estimate the likely dust abundance along a flyby trajectory of a spacecraft, for example, but also to quantify the associated uncertainty.

Results. We present a methodology of the dust environment assessment for the case when the target comet is not known beforehand (or when its parameters are known with large uncertainty). We provide an assessment of dust environment for the CI mission. We find that the lack of knowledge of any particular comet results in very large uncertainties (~3 orders of magnitude) for the dust densities within the coma. The most sensitive parameters affecting the dust densities are the dust size distribution, the dust production rate, and coma brightness, often quantified by Afρ. Further, the conversion of a coma’s brightness (Afρ) to a dust production rate is poorly constrained. The dust production rate can only be estimated down to an uncertainty of ~0.5 orders of magnitude if the dust size distribution is known in addition to the Afρ.

Conclusions. To accurately predict the dust environment of a poorly known comet, a statistical approach needs to be taken to properly reflect the uncertainties. This can be done by calculating an ensemble of comae covering all possible combinations within parameter space as shown in this work.