Tilted Earth

By Neil Comins

It is likely that when the Earth formed, it was rotating (spinning)much faster than it is today and its rotation axis was perpendicular to the plane of its orbit around the Sun. It is currently believed that our Moon was formed when a Mars-sized body, called Theia, slammed into the young Earth and splashed debris into orbit around the planet. This debris quickly coalesced to form the Moon. We don’t know exactly, but it was perhaps 10 times closer then than it is today. When oceans formed on the young Earth, the tides from the closer Moon were 1000 times higher than they are today. Because the young Earth was rotating perhaps 3 or 4 times faster, the day was much shorter. The rapid rotation pulled the monster tide closest to the Moon ahead of the Moon in its orbit. The gravity of that high tide pulled the Moon forward, giving it energy, and causing it to spiral away from the Earth, which it still does today. The energy given to the Moon to enable it to spiral away comes from the energy stored in the rotating Earth. In other words, the Earth’s rotation rate is continually slowing, hence the days are getting longer. The impact also tilted the Earth’s rotation axis to the 23½° that it is today. Seasons are caused by the tilt of the Earth’s axis. When a hemisphere is tilted towards it, the Sun rises higher in the sky and stays up longer (summer) than when that hemisphere is tilted away from the Sun 6 months later (winter).

If the impact of Theia had been at a different angle and/or at a different speed, the rotation axis of the Earth could have been tilted much more than 23½°. Let’s consider what life would be like on an Earth whose rotation axis was tilted 90° so that the rotation axis lies in the same plane as its orbit. The conservation of angular momentum dictates that the rotation axis will always point in the same direction as Earth orbits the Sun. In other words, at one time each year the North Pole is pointing toward the Sun and six months later it is pointing directly away from the Sun. That world would have profoundly different seasons than we do. Imagine that you lived at the North Pole of this tilted Earth. On the day when the Sun is directly overhead, you would look up and see it there 24/7, there would be no night time. As the days passed, the Sun would be lower and lower in the sky, but it would not set below the horizon (no night). Over each day, it would go around in a horizontal circle, each day lower in the sky than the day before,until three months later, it would go around at the horizon and then pass below it. For the next six months it would be below the horizon all day –you would have six months of continuous night. Then it would reappear on the horizon, going around in horizontal circles that would get higher each day, until one year after we started its motion, it would once again be directly overhead. While the motion of the Sun and the day-night cycles would be different at different latitudes, they would all be very different than we ever see on our Earth! While the Moon would have slowed the tilted Earth’s rotation to (roughly) our 24-hourday, the daily and monthly motion of the Moon would also be very different than seen from our Earth.