#Scifi Homecoming had three planets, each with its own ecology. Tourist Trap has two more: Falaron (site of most of the action) and Eversummer. Eversummer had life but not intelligent life when it was colonized, and Falaron was terraformed by the R’il’nai, who transplanted to it the ecology of ice age North America.

Eversummer is interesting not only for its ecology (which I won’t go into right now because it plays a role in the plot of Tourist Trap) but in its physical characteristics. Our own planet has seasons because its axis of rotation is not exactly perpendicular to the plane of its orbit. When one end of the pole is pointed most nearly at the sun, that hemisphere has summer while the other hemisphere has winter. Spring and fall occur when the sun’s rays are just tangent to both poles.

The axis of rotation of Eversummer is perpendicular to the plane of the orbit, and the orbit itself is close enough to circular that the planet stays a constant distance from the sun. The result? No seasons. As Marna sees it:

“The planet, with its rotational axis almost perpendicular to its orbital plane, had no seasons. The poles were bitterly cold, glaciated wastelands where the sun forever rolled around the horizon. The equatorial belt was an unchanging steam bath, the permanent home of daily tropical thunderstorms, varied by hurricanes along its poleward borders. The desert belts, inevitable result of the conflict between the planet’s rotation and its unequal heating by its sun, were broad and sharply defined, with no transition zones where the rains came seasonally. The temperate zones, between desert and polar ice, were swept year round by equinoctial storms, varied only by occasional droughts. No monsoons, no seasonal blanket of snow to protect the dormant land, no regular alternation of wet and dry seasons.

“All of the settled planets Marna had known or studied—long-lost R’il’n itself, Riya, Central, Falaron, Kovee, Earth—had axial tilts between fifteen and thirty degrees, and a regular progression of seasons. Those seasons might be subtle in the tropics, but they were present. And she was beginning to think they were a lot more important than she had ever realized.”

A planet rotating faster than Earth might have more than one desert belt, but with a sun of earthlike distance and intensity, and a similar atmosphere, this is a reasonable description of a planet with no axial tilt.

Monsoons are seasonal wind reversals, so no monsoons. There would, however, be differences between land and water. Land cannot move; any gentling of the difference between maximum sunshine at the equator and zero at the poles must be made up by air motion. On Earth, air and water vapor handle about half of the necessary transfer. Water, however, can move, and heat can be transferred from the equator to the poles fairly efficiently by water. Thus at high latitudes, water will be warmer than land even without seasons. At low latitudes, the land will be warmer than the oceans.

Since surface winds tend to blow from cold to warm, there will be a tendency for the winds to blow from oceans onto shore in the tropics, enhancing coastal rainfall. At high latitudes, the winds will almost always blow offshore, minimizing coastal rainfall.

Further, the requirement of momentum conservation, together with the transfer of momentum between air and ground, will assure that east winds dominate in the tropics, while west winds dominate at temperate latitudes. Thus tropical east coasts and mid-latitude west coasts will still tend to be wet.

What else could be the effects of a pole nearly perpendicular to the plane of a planet’s orbit? Or one where the pole is in the plane of the orbit, like Uranus?

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