HD 63433 is a transit-of-interest, "TOI 1726", with two hot miniNeptunes dubbed b and c; this blog has looked in on c, almost two years back. The system is young; it belongs to the Ursa Major moving-group, formed around the same time - and we're generally moving toward that direction (solar-apex being Hercules), so it's only 73 ly away now. Now [h/t Zimmerman] NASA has brought a third transit, “d”. This returns the system to my attention, as a dynamicist.
Just do not call me a "citizen" in this context. Please.
The outer one, “c”, is a 2.67 R⊕ neptunelike… on the superearth track, losing atmosphere. No such atmospheric loss has been seen in the (now-)middle planet “b”.
“d” orbits close enough I expect it to raise tides on its sun and diiie (mister bond). Meanwhile it should push b to a higher orbit. The outer planet's year runs 17.8 times for every one of our years, so - consider that 17.8 speedup (or more, if c has also drifted) when plotting dynamics.
The known orbits d:b:c are 4.2, 7.1, 20.5 days. If b has drifted out, as I find likely, and if resonances be common in young systems, as others find likely: the outer two worlds b:c used to run more like 6.8:20.4 for a 3:1 resonance. If this resonance did exist, d's inward spiral has pushed out b to break that.
But they're not done. As d augurs in, it will lock into its own resonances. With b: first 7:4, then soon-enough Kirkwood’s 2:1. This could push d’s orbit elliptical as well.
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