Abstract
The ESA mission Comet Interceptor will target an Oort Cloud or interstellar comet during its first approach to the heliocentric distance rh≈1 au, and has been designed to handle the dust loss rate of 1P/Halley as an upper limit of activity level. In the framework of the adopted model of pebble-made nuclei, any extrapolation at rh≈1 au of the dust loss rate observed beyond Jupiter is impossible, because the dust loss rate at rh>3.8 au depends on the nucleus surface area, Ap, composed of water-poor pebbles, whereas at rh<3.8 au the dust loss rate depends on the nucleus surface area, Ar, composed of water-rich pebbles. Pebble-made nuclei are characterized by all possible values Ap/Ar⩾12. The water-driven activity model of pebble-made nuclei has been applied to comets 1P/Halley and C/1995O1 Hale-Bopp. We find that all comets with a nucleus radius smaller than 3.2-0.9+2.3 km will be characterized by a dust loss rate lower than 1P/Halley at rh≈1 au, i.e. will be safe for Comet Interceptor, whichever their ratio Ap/Ar⩾12 will be. We also find that the lower limit of the average refractory-to-water–ice mass ratio of all comets is 3.4.
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