I'm not sure to make an answer out of these for three reasons: 1) it wouldn't be my first rushed, poor quality answer to be outperformed by some better informed, slower respondent, 2) I'm kind of stealing from my working hours, 3) the question is still not properly answered.
@JoonasIlmavirta (forgot to tag in the first place)
@Rafael I combined (and slightly edited) the comments into two longer comments.
@Cerberus True. I hope the current two-comment version is sensible.
@Rafael Totally understandable! It's not bad to post a mediocre answer if you think others are likely to do better. It's still helpful. And I know I've posted numerous less than perfect answers.
But it's up to you, of course.
Rule of thumb: If no one has given an answer explaining what you want to explain, answering is a good idea, even if it doesn't constitute a full answer.
Regarding the planets, two thoughts: 1) a comet is a rare happening, like a couple of days every two years/not sure if we will find a reference for that. Anyway, cometa is Latin, but maybe a Medieval or Modern coining. 2) Asteroids are definitely late-XX-century (Ceres, Vesta, and others were first called planets)
