What would make scientists realize that they are on a toroidal world?

In my story, a portal is opened from the Earth to an alternate world. However, this world is toroidal in shape and has a surface gravity equal to that of Earth. It rotates around an axis that goes through the center of the circle perpendicular to all major radii, and its day/night cycle (assuming that it is inclined enough relative to its star that all (or almost all) of the planet will see sunlight at some point in most day/night cycles. At the location where the portal opens, conditions are very Earth-like (1 atm of pressure with similar Oxygen, Nitrogen, and Argon concentrations, comfortable surface temperature, and 9.8+/-0.1 m/s² of surface gravity after adjusting for centripetal force) and the toroidal shape is not obvious (i.e. on the outer equator).

Some quick sketches of how it rotates (green torus is planet, yellow sphere is its star, black cylinder is the axis of rotation), distances and sizes are not to scale, that I made in about 2 minutes: The axial tilt of the planet may be increased as long as the rest of the planet is moved so that the axis still goes the same way, if that is needed to not have parts in perpetual shadow.

I know that this toroidal shape should not be able to naturally form, but assume that plot device/advanced aliens/a wizard made it stable

What aspects of this planet would tip off the scientists that it is not a sphere like Earth? Would they see something in their surroundings or would they not notice until they either went far enough to see the toroidal shape directly or went into space?

Note that I am not asking for some test to prove that it is toroidal, but rather, something that people would notice is different and would result in them doing those tests or conclusively knowing. It would also be preferable if an ordinary person with a high school education can understand this demonstration (though they need not be able to recognize it on their own or even have been taught in school about it).

posted over 7 years ago

Jarred Allen‭

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