Earth and the Moon are attracting each other through the force of gravity. Image: NASA
The Moon’s orbit around Earth has been regular enough that civilizations have based their calendars on its movements for thousands of years.
However, the Moon is indeed drifting away from Earth. So, will Earth eventually lose its natural satellite?
The Moon is moving away from Earth
According to Live Science, scientists have determined the rate at which the Moon is receding from Earth with the help of retroreflectors placed there by NASA during the Apollo missions.
For over 50 years, researchers have beamed laser beams from Earth to these mirrors and measured the time it takes for the reflected pulses to return.
Using the speed of light, scientists estimate that the Moon is moving away from Earth at a rate of about 1.5 inches (3.8 centimeters) per year, roughly equivalent to the rate at which human fingernails grow, according to NASA.
The Moon is moving away from Earth due to the gravitational interaction between the two. The Moon’s gravitational force pulls water in Earth’s oceans toward it, causing tides. Earth’s gravitational force also exerts a similar effect on the Moon.
The shifting oceans caused by the Moon’s tides create friction on Earth’s surface, thus slowing down the planet’s rotation, as explained by Madelyn Broome, an astronomer at the University of California, Santa Cruz, to Live Science. Around 4.5 billion years ago, “when the Moon first formed, Earth’s rotation rate was significantly faster, with a day length of about 5 hours,” says Broome.
“Because Earth and the Moon are part of the same gravitationally interacting system, the total angular momentum must be conserved between the two. Angular momentum describes the energy contained in something that is rotating. The faster you spin, the more angular momentum you have. The slower you spin, the less,” Broome explains.
However, “it’s not just the spin rate that affects angular momentum. How far away you are from the center of the system matters. Being farther away means the angular momentum of your system increases. Being closer means your angular momentum decreases,” he adds.
According to the University of Arizona, the Moon likely formed from pieces resulting from a collision between a newly formed Earth and an object the size of Mars. Tidal forces have helped draw the Moon to its current average distance of about 238,855 miles (384,400 kilometers) from Earth, as calculated by the Royal Observatory in Greenwich, England.
The tidal effect is also slowing down the Moon’s rotation on its axis, leading to the phenomenon of “tidal locking,” where the Moon consistently shows the same face to our planet. These forces are also decreasing Earth’s rotational speed.
Will this system be broken?
In about 50 billion years, Earth’s slowing rotation will cause it to tidally lock with the Moon permanently, according to Jean Creighton, the director of the Manfred Olson Planetarium at the University of Wisconsin, as reported by Live Science. At this point, the Moon and Earth will cease to move away from each other, says Eric Klumpe, a professor of astronomy at Middle Tennessee State University in the United States.
However, in about 5 billion years, when the Sun begins to die, it will expand into a red giant. “At that time, the Earth-Moon system will almost certainly be disrupted and destroyed,” says David Trilling, chair of the Department of Astronomy and Planetary Science at Northern Arizona University.
In conclusion, the Moon will not leave Earth or vice versa. Instead, the Sun will erase both when it begins to die.