Alfvén systems

I got in my time-machine and am posting on stellar magnetic recombination, today 26 July. Rice publishes this "tomorrow".

Of the exoplanetary systems we know, 1053 stars have a calculable Rossby ratio, of stellar rotation rate to convective turnover time. Thence they calculate Alfvén radius: past which, stellar wind breaks free of the magnetic field. The paper proper uses per-planet "ASHC", Alfvén surface habitability criterion, hoping for greater than 1. TRAPPIST-1 e is here, at around 1.08; "superterran" LHS-1140 b is 1.036.

Thus 84 exoplanets in our sample have orbits which lie inside the CHZ and that also lie outside the star's Alfvén surface: 34 of these have been classified as terran (11) or superterran (23) planets. For those interested here's raw data (text).

Most dwarf planets of stars as have been spotted are transits of M dwarfs. They trend inside Alfvén so they lose atmo. Proxima Centauri b was always deemed a blasted wasteland; it is inside the Alfvén sphere too. Ross-128 b is another one ruled-out; UPDATE 7/27 as are both GJ 1002 planets especially the inner one. And this blog has never taken TRAPPIST-1 b,c,d seriously.

Just because some planet is free of ASHC=1 doesn't mean we can pack our bags. TRAPPIST-1 e is argued in a 2019 paper as not sufficing in magnetic-moment. Escaping all the nets are only two: K2-3 d and Kepler-186 f; I am unsure why we're not talking K-452 b and the other potential photosynthetics. As to ice worlds as can ignore sunlight, I don't know that such be possible beneath ASHC although LHS-1140 c comes close.

I must repeat: our sample is weighted heavily toward transits (so too close) and obviously-uninhabitable giants. Earthlikes at 0.8 AU from K stars, or 1 AU from G like us, might not be possible to spot from here.