HD 110067's six hellworlds

Last night a few science-alerts got loose about HD 110067. That Henry Draper catalogue-number means it was among 225300 stars which Annie Jump Cannon catalogued as of 1905 and published up to 1924. So: it's nearby and bright, as these things go: about a hundred light years off and a K type. It is now in the news for having six (6) planets.

You'll not want to visit any of them. They were found not by radial-velocity of the star but by transit. Indeed, they are close to the star: the outermost orbits just under 55 days, which is near exact 5/8 Mercury. These will be superheated by their sun.

And they orbit in mutual resonance - close resonances, to the tunes (heh) of 3:2 for bcde and then 4:3 for efg. (Opposite from what I proposed between Europa and Ganymede; that was 4:3 then 3:2 within E:G's 2:1.) We need to consider tides. Somehow the innermost planet has managed not to get pulled inward by its sun. That energy is probably getting eaten up by tides internal to the planets. Yikes!

The good news about transits is that they deliver the radii (as a ratio of their sun) for all the occultations. They also have the mass-ratios of the inner planets b, c, d against their sun - hooray for Kepler. The three inner worlds seem puffy, which is impressive for such hot planets, as 4 Gy old as the system is. Further: the resonance is assumed to be a holdover from formation. Chaos doesn't normally resolve into 3:2 and 4:3 resonances. Without chaos in the system these close-in planets, further, aren't getting Theia - they aren't getting moons.

Much of the research was done by the CHEOPS 'scope down here. We all know the unfortunate rules; the longer the period between transits, the less well we know the parameters. They want to target the 31-day "e" planet, to constrain that one's mass. And maybe Webb can hit the system for infrared.

We are lucky to have this one in transit. I expect K or G stars exist, closer than 100 ly, as own resonant inner planets not in transit. That's a matter for closer inspection of spectral time-series.