<p>The practical limitations inherent to human and robotic planetary exploration necessitate the development of specific protocols, instrumentations and methods. This non-standard approach implies testing and validation phases in order to optimize the setups and to improve the scientific interpretations prior to, during, and after a mission. These tests are made either using space instruments or representative systems and are carried out on &#8216;analogue samples&#8217; and/or in &#8216;analogue sites&#8217;. Analogues can be globally defined as objects or sites having compositions and/or physical properties similar to specific extraterrestrial objects.</p>
<p>Nevertheless, due to the variability in composition and properties of natural materials, there are always &#8211; inevitably &#8211; some differences between the analogue and the object(s) to which it refers. In studies using analogues, it is thus important to focus on the specific properties that need to be imitated and to consider analogue properties rather than analogue sites or samples alone.</p>
<p>Thus, we recently introduced the concept of &#8220;functional analogues&#8221; (Foucher <em>et al.</em>, 2021). &#160;Functional analogues are defined as terrestrial sites, materials or objects exhibiting general properties more or less similar to those anticipated on the targeted extraterrestrial body, but having specific analogue properties that are highly or perfectly relevant for a given use.</p>
<p>Based on this definition, we sorted functional analogues according to their utility for different domains, from engineering to astrobiology, throughout the timeline of space missions. We also proposed logical pathways to facilitate the selection of the best-suited functional analogue(s) according to their intended use.</p>
<p><em>Reference: Foucher, F., Hickman-Lewis, K., Hutzler, A., Joy, K.H., Folco, L., Bridges, J.C., Wozniakiewicz, P., Mart&#237;nez-Fr&#237;as, J., Debaille, V., Zolensky, M., Yano, H., Bost, N., Ferri&#232;re, L., Lee, M., Michalski, J., Schroeven-Deceuninck, H., Kminek, G., Viso, M., Russell, S., Smith, C., Zipfel, J., Westall, F., 2021. Definition and use of functional analogues in planetary exploration. Planetary and Space Science 197, 105162.</em></p>
The selection of comets for future space missions