TOI-1136

TESS the transiting-planet scope found an object of interest around the Praesepe cluster 276 light-years off, so within that (low) double-digit parallax. There's arXiv for details. h/t Planet B's NASA writeup

The planets are all transits so they are all very close to the star - which is pretty-much our own Sun at 700 million years old (1.022 ± 0.027 M_☉). So the planets are all horrible.

Of interest to me is firstly the planets' resonance - there is one, there might have to be one, as close to the star as they are. But it's not as Laplacian as those of TRAPPIST or, er, Jupiter I-III. Remember that it's all still young, if 100 My older than Kepler-221.

Their masses are estimated by transit-timing-velocity. Not radial-. As they note, radial has a bias toward high-mass for the radius i.e., high density. Until we get to 8 M_⊕.

Fig 17 shows the masses and radii. Logarithmic scale - this to include the Neptunians at <20 M_⊕. Error bars are high; so they didn't bother giving us a numeric table. Japanese wiki says total mass: 35.51 M_⊕ which is slightly more than Uranus+Neptune together. Gliese 876 b is 2.66 M_J. Innermost b is as dense as water; that’s the densest.

How did all these form separately rather than coalesce into one big ugly Hot Sub Saturn. To that their system seems near-perfect: no perturbations from the other Praesepiae.

Tidal energy is a demonstrable Thing for Laplacian worlds. This is estimated at 1e+16 W for planets d and f (implicit). Planet d is getting 1e+20 W “bolometric”, which must mean calculated from the bolometric luminosity (effectively solar), inverse-square planet-distance and (I think) integrated over surface-area which for order-of-magnitude can just be πr², 156.75 times that of Earth. Anyway the tides are negligible relative to raw sunlight.

“Solar-constant” insolation over here is, as this blog keeps repeating, 1380 W/m²; but sometimes they lowball the total 1.74 e+17. Anyway: 1136d is getting three orders of magnitude more sun than we get.

Compositionally I suspect our “water density” baseline is the Hot Ice: VII at 3+ GPa, under a superheated liquid-water ocean. The authors cannot account for this for the planets c-on-up, so propose further envelopes of hydrogen (even helium). As for b that’s puffy rock since it’s not pushing tides against the other planets.

Even then, d and f look too puffy and might contract in future. The authors request more time from the JWST because of course they do.

The article posits (over and over!) that planets e and f, at 7:5 resonance, will likely not stay there. One or both of these will find its way out - or in. One might see a Theia opportunity in this system's future especially if perturbed. If not the authors muse about near-resonance, like Earth/Venus or Saturn/Neptune.

Also here is disc density, within 1 AU anyway. By extrapolation the system has already sucked up available material in its habitable-zone, so has no Earth. I can’t see this system tossing an Earthlike into that region either. But I’d not rule out more super-earths or ice-giants 2+ AU (which we’ll not see from here).