Scientists spot 6 alien worlds orbiting a star in strange — but precise — harmony

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