What’s strange is that these Martian wobbles happen at local midnight, as if responding to the demands of an unseen, nocturnal timer.
That’s a new one on me. I goptta say, I have never heard that one.
PIF: Correct. That’s when Mars’ gravity wave generator is pointed towards its long vanished target, gone nearly a billion years now. See 41
But the "midnight" repeatedly mentioned in this article is always referring to local midnight - i.e., when it is midnight at the longitude of InSight.
There is nothing "special" about that particular landing site nor about its local midnight - InSight could just as easily landed at any other longitude; it would then have still registered this phenomenon (your "gravity wave generator") at its (other) local midnight.
Thus, this phenomenon could be better described as constantly occurring at that side of Mars momentarily opposite to / farthest from the Sun. Which also means that your "gravity wave generator" is not pointing at any fixed target, since Mars revolves around the Sun once every Martian year (approx. 1.88 Earth years).
Think: Welding a machine gun to a Merry-Go-Round, facing outwards, and then setting the Merry-Go-Round into motion.
Even if your "gravity wave generator" were restricted only to InSight's lcoation, it still holds that Mars is constantly revolving around the Sun, and so that local, InSight-specific "gravity wave generator" would be pointing to a different direction of the Martian sky every midnight.
Regards,