Geneva reports on a discrepancy between masses estimated by transit-timing and by good ol' radial spectra. I actually didn't know that transits even yielded mass rather than just relative radius (so volume).
They answered the question by noting that transit-timing tends toward resonant orbits. Because they're tightly packed. Because they're close to the star. The discrepancy is, then, with the resonant planets - which are indeed less dense.
Again here's something I'd not expect; I'd expect those to lose their atmo and become rocky. But if they're subNeptunes around red dwarfs then maybe not. They just heat up their atmo to be puffier. The paper would further suggest that in resonance, they are not bashing into each other, so can keep more volatiles than our own collison-happy inner planets kept.
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