Relative pronouns perform as 'conjunction + pronoun'.
Of course "Hayabusa" is not actually closing in on the Sun, it is just positioned as in the figure so that, seen from the Earth, it is on the opposite side of the Sun; this is called 'conjunction'.
A more plausible proposal is the one Leech presented in conjunction with Emmet's theory.
In English there are eight main parts of speech: noun, verb, adjective, adverb, pronoun, preposition, conjunction and finally interjection.
The shoulder joints, as well as moving on their own, also move in conjunction with arm movements.