[Keysh]

OK, you're really not making much sense. I mentioned exoplanets because that was a (barely) plausible interpretation of something that was a "hot field in modern astronomy but was barely a thing when JWST began", since the preliminary studies for JWST did happen in the mid-1990s, when exoplanets were first beginning to be found. The actual serious design work, though, was in the early 2000s, when exoplanets were definitely a hot topic.

But if what you really mean is "within the solar system" (which, um, excludes "Tabby's star"), well... "barely a thing when JWST began" is complete nonsense. I mean, studying things within the solar system is something astronomy has been doing for literally thousands of years. (And, no, it hasn't suddenly become "the hot field" in any sense, leaving aside the point that there are multiple things that might be considered "hot fields" at the moment, and that there's never a single "hot field" anyway.)

JWST is perfectly useful for solar-system science: there are about 22 approved Cycle 1 General Observer proposals in that field, including one specifically meant for any "interstellar object" (like 1I/'Oumuamua or 2I/Borisov) that might show up during the first year: https://www.stsci.edu/jwst/phase2-public/2337.pdf

And the second-largest set of Guaranteed Time Observation proposals (proposals from "scientists who helped develop the key hardware and software components or technical and inter-disciplinary knowledge for the observatory"), after "Extra-solar Planets", is "Solar System": https://www.stsci.edu/jwst/science-execution/approved-progra...