What if the moon came closer

Moons are natural satellites, i.e., astronomical bodies that orbit a planet. Different planets have different numbers of moons, with our dear earth having a singular moon with the Latin name Luna. It is four times smaller and 81 times lighter than the earth and orbits at a distance of 3.8 million kilometers.

We all know gravity makes things fall back to earth. Many also know it is a mutual attraction between bodies, so the moon and the world are constantly pulling each other. The moon doesn’t just crash because it is on an orbital path. It always falls, but it moves horizontally to the surface, so it just curves away and cannot get closer. To understand better, imagine throwing a rock along the surface. The harder you throw, the further it will land along the round surface of the earth. If you throw hard enough, it will circulate the planet and start orbiting it. Here is a depiction of this by Isaac Newton

In reality, the moon is drifting away from us at a rate of 4cm a year. But let’s suppose hypothetically, it sped up and came slightly closer. The effects will be devastating. It will lead to a greater gravity from the moon. The earth will spin slower, making the days much longer with more frequent eclipses. It will also trigger numerous earthquakes leading to several volcanic eruptions. If someone can survive the massive chaos, at least they can enjoy a much bigger and brighter moon in the sky.

Let’s assume the moon stops rotating and starts falling towards the earth. If any humans were somehow able to survive, they would be wiped out by the catastrophe. With a gentle contact from the moon with an impact velocity of 30 km/s (minuscule regarding celestial bodies), the earth will instantly superheat, destroying all existing life. It will lose a lot of its mass with several shockwaves all across the globe. All the water will be vaporized along with massive volcanic events. There will no longer be an atmosphere with highly erratic temperatures everywhere.

One of the primary responsibilities of our moon is to maintain tides. The gravity from the moon causes the water on the surface of the earth to bulge in its direction, causing differences in the height of water surface level on different coastlines. The bulge towards the moon is called the high tide, while the sides get squished and are called low tide. If we apply the above scenario to tides, the earth will be destroyed long before the moon even touches the ground. As the force of gravity starts increasing dramatically, the effect of tides will rise exponentially. The high tides will result in tsunamis that will flood half the earth. The side experiencing the low tide will start getting crushed under high pressure. The earth’s spin will be slowed by the friction between the water and the surface, which might even knock the world out of its orbit.

The positions of the planets and the moons are essential to sustain life. We are fortunate to have an almost perfect setup solar system. However, it is always good to hypothesize these exciting situations as they help us learn how things work and prepare us for unforeseen disasters in the future.

Written by Sajal Agarwal

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Techniche, IIT Guwahati

Techniche, IIT Guwahati

IIT Guwahati’s annual Techno-Management Festival — the largest of its kind in North East India. We have gone virtual this year! Visit us at techniche.org