Earth as a Moon

By Neil Comins

Our Earth and its companion Moon, which has about 1/81 as much mass as the Earth,waltz together around the Sun. Earth’s strong gravitational attraction created tides on the young, molten Moon, causing that smaller world to rotate (spin) at the same rate that it revolves (orbits) around the Earth. As a result, standing on our Moon, you would see the Earth at a fixed position in the sky or, if you were on the other side of the Moon, you would never see the Earth. In this new world described below, we have reversed the roles on the Earth and Moon, so that now the Earth is a moon of a larger world. In the realm of attracting young people to STEM, this is a plausible physical scenario because our solar system has four planets that are larger and more massive than our Earth. In a different star system, the most massive planet in our solar system, Jupiter, might be where we are now and it could be orbited by an Earth-like world.

What would life be like on the earth-like world, let’s call in Mynoa, orbiting a larger planet (Tyran)? As we have already noted, Tyran would be fixed in the sky, depending on your longitude and latitude. Because it is so close and so much larger than our Moon, Tyran would be larger in the sky than the Sun. As Mynoa orbits around Tyran, you would see the Sun and stars move across the sky, but Tyran would remain fixed. Because Tyran appears so large, each day the Sun is eclipsed by it for several hours. During that time, which is around noon each day, the temperature and winds will fall. It is likely that Mynoa’s rotation axis would not be tilted, like the Earth’s rotation axis, which is tilted 23½° from being perpendicular to our orbit around the Sun. That tilt gives us seasons, so Mynoa will not have seasons. Mynoa will have tides 1/3 as high as ours, created by the Sun, which also creates 1/3 of our tides. Depending on the version of Tyran we choose, it could have oceans and life. Traveling there from Mynoa and exploring it, with its greater gravity than on Mynoa, will be a great adventure!