29 Cygni

Thayne Currie et al. report a new planet. Literally new; it likely formed during our own Caenozoic. Also new-ish here is a call to redefine "planet" upward in mass, of this one's 15 Jupiters.

ScienceDaily led me to a UT-San Antonio presser which, frankly, is bad. Luckily a little searching afield leads to better pressers, like Keck's (telling us how far it is) and Subaru's. And the arxiv. I should have been reading galaxy_map last night but I was watching Return of the King at the time. Anyway.

The star is 29 Cygni, for whatever reason being called "HIP 99770" here (dudes: tell us the constellation at least, plz). Part of the job of constraining the system was to constrain the star, through Gaia DR3 and better imaging, made possible by its double-digit parallax: 132.8 light-years away, bit further than HR 8799 over in Pegasus. The star is young at about 40 My, and shines as an "A" white star about double our sun's mass. Luminosity is, of course, much higher than twice ours. I think it's on the main-sequence now so, this is about as cool as it gets.

What happened here was a starfield of northern-hemisphere highish-parallax which they watched for 25 years. In that quarter-century, some slow variables trickled through the filter. If the period was long enough - and since they know the star's mass because, hey, main-sequence - they could get a handle on its semimajor; therefore by Kepler its mass-ratio. If close enough to our 'scopes, they might be able to see the planet itself. Especially if the planet is hot. Which, at 40 My and at that 15-Jupiter mass, it probably would be.

The Subaru over in Mauna Kea has not disappointed the San Antonians. One excellent feature of their presser is its diagram of the system as related to Earth's on a flux scale, of irradiance, showing how this planet lives near-exactly on the Jupiter belt. The planet is far hotter than Jupiter though: 1400 K. I take it that if it were a brown dwarf, it should be hotter still; so they're marking it as a planet. Thayne Currie explains his team's call.

Seems like it might be non-dense if it's not doing any fusion. More lithium in its core might spark it. So I expect it is rather larger than Jupiter in size but will contract as the leftover heat radiates out.

I don't know if this system has formed other planets. I'm guessing that if Saturnlikes orbited this star inbound of this monster, we'd know. Might not see 'em, but we'd see the stellar wobble and take a guess at their inclination. The system is young enough that dynamical instability shouldn't have turfed out any Earth-mass planets in its habitable zone.

So: what about their future. Our own Jupiter, gravitationally 7.5 times weaker than this guy, has obviously caused a mess in our inner solar-system such that little but Mars and Vesta could form and stay between 1-5.3 AU (plus those Cerean interlopers). But much of that was because of the Grand Tack where Jupiter and Saturn both were migrating in and out. If 29 Cygni has no Saturn, which I doubt it has, then there's no Tack and the inner system is left more stable.