According to Live Science, the Moon’s orbit around Earth, which seemed regular enough for some civilizations to rely on its motion for calendrical purposes, is now being found to be slowly departing from our planet, causing worldwide oceanic bulges.
Scientists have determined the rate at which the Moon is drifting away from Earth using reflectors placed on the celestial body by NASA during the Apollo missions.
For over 50 years, laser beams from Earth have been directed at these reflectors, and the resulting reflections have been recorded, helping NASA estimate that the Moon is moving away from Earth at a rate of about 3.8 centimeters per year.
Earth as seen from the Moon – Photo: Jeremy Horner
While this rate is equivalent to the pace at which human fingernails grow, the accumulated distance over the incredibly long lifespan of astronomical objects poses a significant concern.
The Earth’s oceans are bulging toward the Moon due to its gravitational attraction, while on the other hand, our “companion” is gradually acquiring an oblong shape as it experiences gravitational interaction from Earth’s pull.
Astronomer Madelyn Broome from the University of California, Santa Cruz, has explained that approximately 4.5 billion years ago, when the Moon was newly formed, Earth’s rotation was considerably faster, with a day lasting only about 5 hours.
At that time, the Moon was much closer to Earth, and the two celestial bodies were constantly exerting influences on each other. The gravitational force from Earth’s tidal bulge affected the Moon, while in return, the shifting oceans caused by the Moon’s gravity created friction on Earth’s surface, causing it to slow down.
Because Earth and the Moon are part of a gravitationally interacting system, the total momentum of the system must be conserved. Momentum (also known as rotational momentum) represents the energy contained in something that is rotating. The faster the rotation and the farther apart the two objects rotate, the more energy is present, and vice versa.
Therefore, when Earth slows down—just as the Moon has slowed down in the past—the two bodies must have balanced the total momentum of the system by moving away from each other. The Moon has taken its share of the movement.
The Moon no longer slows down today, as it has long ago come to a halt and is “tidally locked” with Earth, meaning it only shows one face towards our planet.
Models indicate that eventually Earth has chosen to “grasp” the Moon by also tidally locking itself, facing the Moon with a single side so that the Moon no longer recedes.
According to Dr. Jean Creighton, director of the Manfred Olson Planetarium at the University of Wisconsin-Milwaukee, and Professor Eric Klumpe from Middle Tennessee State University, this will occur within the next 50 billion years.
However, unfortunately, the parent star of both—the Sun—will deplete its energy and evolve into a red giant before collapsing into a white dwarf in approximately 5 billion years.
During the expansion into a red giant, the Sun is predicted to engulf some of the nearby planets, including their satellites, of course.
Earth is on the list of being “swallowed” according to calculations. This means that both the Moon and Earth will disappear together long before they decide to stop rotating.