For 4.5 billion years, the Moon has accompanied the Earth as a natural satellite. Looking at the sky and observing it has become a habit, as if the Moon were an immutable and familiar object, an eternal partner of our planet. However, what would happen if it were to disappear?
The Moon is larger and more massive than any other natural satellite relative to the planet it orbits (ratio of satellite to planet size). Connected for thousands of years to traditions and myths, our natural satellite is also responsible for many terrestrial physical phenomena. Losing the Moon would be catastrophic for the Earth and humanity, as it would lead to irreparable changes in our environment.
A collision with a sufficiently massive object could not only deorbit the Moon, but also pulverize it. Debris would spread in all directions. Depending on the intensity of the blast, the scenario would be different:if the blast is weak enough, the debris would reform into one or more new moons; if it is too strong, the lunar pieces would be reduced to dust; if it is of an intermediate power, the debris would form a ring system around the Earth.
Over time, these lunar fragments would de-orbit due to Earth's atmosphere, creating a series of impacts. But those impacts wouldn't be as destructive as the asteroids or comets being monitored today. Even if the Moon chunks were massive, dense, and even potentially larger than the asteroid that wiped out the dinosaurs, they would have far less energy.
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Asteroids or comets that strike the Earth move at a speed of 20, 50 or 100 km/s, but lunar debris would move at a speed of only about 8 km/s, and would be mostly disintegrated by our atmosphere. The few pieces of debris hitting Earth would be potentially destructive, but would hit the surface with less than 1% of the total energy of a comparably sized asteroid. If the pieces that would hit us were small enough, then humanity could easily survive.
Once the Moon and all its debris disappeared, the second-brightest object in Earth's sky would have completely evaporated. While the Sun is naturally 400,000 times brighter than the full Moon at its perigee, the latter is 14,000 times brighter than the other brightest object in the sky:Venus.
On the Bortle scale (a scale measuring the level of brightness of the night sky), the full moon can shift a level 1 sky—the most naturally clear and deep sky possible—to a level 7/8 sky, obscuring almost completely the brightness of the stars. Without the Moon, there would no longer be any natural obstacle to a luminous starry sky every night of the year.
Eclipses require the alignment of three objects:the Sun, a planet, and the planet's moon. When the moon passes between the sun and a planet, a shadow can be cast on the surface of the planet (total eclipse), the moon can also cross the surface of the sun (annular eclipse) or block out a fraction of the sunlight ( partial eclipse). But without any moon, none of this could happen. Our only natural satellite would never pass through Earth's shadow if it didn't exist, thus ending eclipses.
The Moon exerts a certain frictional force on the rotating Earth, slowing this rotational speed over time. The 24-hour day was only 22 hours when dinosaurs roamed the Earth, and it was less than 10 hours a few billion years ago.
In four million years, leap days will no longer be necessary in our calendar, due to the slowing of the rotation speed and the length of the day which continues to lengthen. If the Moon disappeared, then this phenomenon would also disappear with it. The days would remain fixed at 24 hours until the Earth itself was swept away by the end of the Sun's life.
High and low tide are a big difference for those living near the coast, especially those in a bay, inlet or inlet. The tides on Earth are mainly due to the Moon, with the Sun contributing only a tiny fraction of the tides.
During full moons and new moons, when the Sun, Earth and Moon are aligned, these are the spring tides, leading to the greatest differences in level between high tide and low tide.
During the half-moons, these are the smallest tides (new tides), where the differences in level between high and low tide are minimal. Spring tides are twice as large as new tides, but without the Moon the tides would still be the same paltry size and only a quarter of the size of current spring tides.
The Earth rotates on itself, inclined at 23.4° with respect to our orbital plane around the Sun; it is the obliquity. Over tens of thousands of years, this tilt has varied from 22.1° to 24.5°. The Moon is a stabilizing force, as worlds without large moons — like Mars — see their axial tilt change ten times more over time.
On Earth, without a moon, it is estimated that the obliquity could sometimes even exceed 45°. The poles would not always be cold; the equator would not always be warm. Without the Moon to stabilize the Earth, glaciations would preferentially affect all regions of the world, every few thousand years.
This instability could cause significant changes in climate cycles. The seasons could become unstable and more violent.
One of the reasons why man was able to walk on the Moon, from 1969 to 1972, is due to the proximity of the Moon to the Earth. At just 380,000 km, a conventional rocket can make the trip in about 3 days, and a round-trip signal at the speed of light takes only 2.5 seconds. The other nearest bodies, Mars and Venus, require months of travel, more than a year for a round trip and many minutes for a round trip communication. Without Moon, it is our closest access platform to space that disappears.
