Lowell's Mercury

I'm going to use Mercury as a testbed for Lowell Was Right!. Mars and Venus would be too close to pulpy, because the underlying assumptions were those of late 19th century science, as most of the pulp authors were raised and educated under those assumptions. Mercury, however, was seldom discussed in Pulp fiction, so I think I am am safer in getting the feel right.

Lowell's Mercury will be tidally locked to the sun. This was the understood opinion until 1965, when radar returns indicated it had a 3:2 rotational resonance. Its orbit is extremely non-circular, giving it "seasons" with a perihelion summer and aphelion winter. We are assuming a standard oxy-nitrogen atmosphere generated by the life on the planet. In order to retain a significant atmosphere, Mercury would have to be denser than Mars, so a high proportion of metals to silicates and a large metallic core are reasonable.

The atmosphere mitigates both the extreme heat of the Sunward side and the extreme cold of the Darkward side, with strong air currents moving cold air from the Darkward side close over the surface to the Sunward side, with high hot currents moving hot air back to the dark. These winds would be constantly blowing from Darkward to Sunward, with no coriolis forces to twist them. They would also be very strong.

Water circulation would be meltwater from the glaciers and icecap on the dark side. These would accumulate in a bitterly salty sea on the Sunward side and evaporated into the hot atmosphere. The high, hot winds rushing Darkward would start to precipitate water out starting near the terminator as the air cooled.

A belt of land extending from about 15 degrees Sunward of the equator/terminator to about 5 degrees Darkward would be habitable, about 450-600 kilometers wide. Meltwater rivers would come down from Darkward and wind through the belt into the hot lands further Sunward,  where they would reach the bitter ocean, or evaporate.

Mercury was colonized long ago by the Martians, as the gravity was congenial. The higher plants and all animals on Mercury were brought by them either from Mars, or from Earth or Venus. The Martians on Mercury were left to their own devices when the Martians retreated to Mars during the Troubles, and are consequently far less hidebound than those on Mars. There are humans as well, all servants of the Martian Great Houses, or travelers from Earth.

-clash