On topic of TTV, a habitable-zone planet was just found through its effects on Kepler 51d. The perturbator, which sounds dirtier than it is, would be "e". Year is 264 Earth days, so d:e is not-quite 2:1. e is also noneccentric, so would be Venuslike here; but for K-51-A which is a lighter star and new to the mainsequence (I'll get to this) e's Earthlike.
... but very heavy. e is a miniNeptune like the other three "cotton candies". I think TTV allows some constraint on true mass given that we do, in fact, know the masses of the b,c,d. Better now, in fact.
I didn't say superearth. Yes e doesn't transit; yes that means we don't know its volume. I can guess, though, that if the inner planets are puffy and hydrogen-rich then, so much more so this Sudarsky-II outer planet. Barring some crazy impact event but then, wouldn't its eccentricity match that?
The star is young; it spins eight days and (I learn) astrologists (heh) consider this a 500 My age. There is also noise from activity. Youth would assuredly explain why the inner worlds haven't lost their (opaque) clouds yet. Mind, this extreme youth further suggests a coming expansion of the HZ leaving e too hot. Well, e's moons, that is; although if it's got any I expect them to look like Ariel over around Uranus.
It took fourteen Earth years to spot d floating into transit so early. The virtues of patience. Maybe the improved maths we're promised will help find these things faster.
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