Comet Interceptor will fill a gap in the in-situ study of comets. All previous comet encounter missions have visited short-period comets, which have relatively quick orbits (with periods of less than 200 years) and have traveled into the inner solar system many times. As a result of their repeat close passes by the Sun, short-period comet nuclei are baked, blackened, and decayed remnants of their original icy selves. In contrast, NASA’s New Horizons recently visited a pristine icy world of the Kuiper belt, the object named 2014 MU69, which has never traveled closer to the Sun than its current position. Comet Interceptor hopes to get our first look at a long-period comet: a body that formed even farther away than MU69, in the Oort cloud, that is making its first pass into the inner solar system and actively undergoing transformation from a frozen world into a spectacular comet.

The challenge for intercepting a long-period comet is that we don’t usually have a lot of time between our discovery of them and their arrival in the inner solar system. Typically, we first observe these worlds months or, at most, a few years before their arrival, not enough time to develop and launch a spacecraft. Comet Interceptor will solve that problem by launching before a target is discovered. It will piggyback to space aboard the same rocket that launches ESA’s exoplanet-survey spacecraft Ariel, an event nominally planned for 2028. (Comet Interceptor would be delayed by any Ariel launch delays, but its mission would not be harmed by such delays.) Following Ariel, Comet Interceptor will travel to the Earth-Sun L2 point, where it will await the discovery of a new long-period comet.