Interesting reports out on TOI-178 multiple exoplanet system now. My observation. The NASA ADS Abstract, Six transiting planets and a chain of Laplace resonances in TOI-178,
https://ui.adsabs.harvard.edu/abs/2021arXiv210109260L/abstract, January 2021. The arXiv paper is attached. I would call this system, orderly orbits, disorderly densities
"This contrast between the rhythmic harmony of the orbital motion and the disorderly densities certainly challenges our understanding of the formation and evolution of planetary systems," says Leleu",
https://phys.org/news/2021-01-puzzling-six-exoplanet-rhythmic-movement-theories.html
From the arXiv paper, "In total, we therefore announce six planets in the super-Earth to mini-Neptune range, with orbital periods from 1.9 d to 20.7 d, all of which (with the exception of the innermost planet) are in a 2:4:6:9:12 Laplace resonant chain. All the orbits appear to be quasi-coplanar, with projected mutual inclinations between the outer planets estimated at about 0:1 deg, a feature that is also visible in other systems with three-body resonances, such as Trappist-1 (Agol et al. 2020) and the Galilean moons. Current ephemeris and mass estimations indicate that the TOI-178 system is very stable, with Laplace angles librating over decades...We note that, for a star such as TOI-178, the inner boundary of the habitable zone lies around 0.2 AU, or at a period of the order of 40 days. Additional planets in the Laplace resonance could therefore orbit inside, or very close to, the habitable zone."
On page 4, TOI-178 stellar mass is listed, 0.647 solar masses with age 7.1E+9 years old. On page 26, "Table B.2. Mass estimation with activity model as two sinusoids, Halpha model, and correlated noise." gives mass stats for TOI-178 b through TOI-178 g, ranging from 1.5 earth masses to 8 earth masses. These exoplanets sites are still pending showing these six as *confirmed*,
http://exoplanet.eu/catalog/,
https://exoplanetarchive.ipac.caltech.edu/index.html
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