Space/Science — HabitableZone

Space/Science » in reply to re: Solar wind

"day" and "year"
nick hoffman — (archived)

Well, it depends how you look at it. For a fully-tidally locked body, half the planet has no day, and the other half no night, The important thing is that although the same face is always facing the Star, the planet is still spinning - one revolution per year. We don't really have the words in our everyday language to describe some of the stange possible effects of orbits and rotation when the parameters are very different to earth.

Consider Uranus, which is essentially tipped on its side (spin-axis is essentailly in the plane of rotation). Some parts of its year, there is a regular day-night cycle with the Sun near the equator. Other parts of the year, the sun is above one or other pole and you have "perpetual" day or night.

Why does the spinning matter? Because if there were NO rotation, then convection of the core would be much less likely to generate magnetic fields, and it is generally felt that a good magnetic field helps protect the atmosphere and biosphere of a planet.

For large enough planets, the atmosphere is safe - Venus has a very healthy atmosphere despite its high temperature and lack of magnetic field, so this uber-Earth would have no real danger of atmospheric loss, and the atmosphere itself will help protect the biosphere...

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