Saturday, October 8, 2022

Mercurylikes aren't habitable

Around our Sun, the planet Mercury used to be thought as tidally-locked. Instead it has a day-year resonance leading to some very weird sunrise / sunset patterns. Also its orbit is eccentric such that it floats 0.3-.46 AU.

Mercury isn't considered habitable excepting maybe its poles. Even electronics don't do great down there. Off and on, though, I've been wondering about such stars as do own habitable-zones encompassing up-to-0.4 AU. Those would be the K stars. Plus eccentricity is supposed to be good now.

Except that K gravity is 0.5-0.8 M. The 0.3-.46 AU range would be more like 0.21-.32 AU if half Solar; 0.27-0.41 if skating G. 0.4 AU is on the inner bound of K's red-heavy emissions. For reference a K5V (0.70 M) stays Venereal out to 0.68 AU. Goldilocks planets will have rotations and revolutions on their own, nonresonant schedules just like we do (and like Venus does whilst we're at it).

In sum, I doubt any Spaceman Spiff will be observing a Mercurian sunrise over any planet anywhere. Unless he's under a dome in a Mercury-mass planet with atmosphere and temperature swings like our own Moon.

THE BLACK HOLE LIBRATION 11/4: Consider a 25 M, with a G class 1 M around that. A L4/L5 planet's oscillations in orbit could well force a 2:3 (or 3:2) rotational symmetry. If the central mass is a black hole, after clearing its vicinity it gives off negligible heat - given how we've not found many directly. That planet should get Solar irradiance.

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