Did the Earth once have a second moon, and if so, what happened to it? Did it fly into outer space? Or collided with another moon? Could the loss of the Earth’s second satellite be the reason for the different structures of the far side of our present moon? It’s time to explore another cosmic secret.
Theories of the Second Moon
The idea that there was once a second moon on our planet goes far into the past.
In 1846, French astronomer Frederic Petit, a director of the Toulouse Observatory, announced that he had discovered a second moon in an elliptical orbit around the Earth. His assumption was not confirmed, but the story became the plot in the science fiction novel of Jules Verne of 1870 “Around the Moon.”
A few years later, in 1898, Georg Waltemath, an astronomer from Hamburg, announced that he had discovered not only the second moon but a whole system of tiny moons. But his discovery was also not confirmed by the scientific community.
American astronomer William Henry Pickering (1858–1938) studied the possibility of a second satellite on our planet and suggested that the moon itself is a fragment of the Earth.
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Collision of two Earth satellites
If we move to the present, we will learn about the intriguing theory proposed by Erik Asphaug, a planetary scientist from the University of California at Santa Cruz and Martin Jutzi from the University of Bern.
According to Asphaug and Jutzi, it is possible that the Earth had another moon billions of years ago. The two moons coexisted in harmony for tens of millions of years.
Both satellites would form from the debris that was thrown when a protoplanet the size of Mars crashed into the Earth at the end of its formation. While the traditional theory claims that the young Moon destroyed any rivals or gravitationally threw them into interstellar space, the new theory suggests that one body survived, gaining ground at a gravitationally stable point in the Earth-Moon system.
Meanwhile, the tidal forces of the Earth caused both moons to move away from our planet. When they retreated to a distance equal to about 1/3 of the present to the Moon (a process that took tens of millions of years), the gravity of the Sun led to the instability of their orbits. And when this happened, they collided with each other. The smaller moon was destroyed, and its remnants merged with the larger satellite, literally “smearing” with a thin layer on its surface.
Asphaug and Jutzi conducted several computer simulations of the collision, showing that the current state of the moon can be explained by a collision with a small body about 1000 kilometers in diameter. Traces of this “other” moon are preserved in a mysterious dichotomy between the visible side of the moon and its distant edge
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On the visible side of the moon, low-lying lava plains prevail, and on its reverse side, highlands. But the contrast is not only that. The bark on the far side is 50 kilometers thicker than in the near. The near side is also rich in potassium, rare-earth element, and phosphorus – components are known as KREEP. They would be concentrated in the last remnants of underground magma and crystallize upon cooling of the moon.
Asphaug is sure that this suggests that something “squeezed” the KREEP layer on one side of the moon, long before the rest of the crust hardened. Exposure, he believes, is the most likely explanation for this.
Asphaug and Jutzi are of the opinion that the mountains on the far side of the moon are the remnants of a crashed satellite.
This is an interesting theory that can explain why the two sides of the moon are so different.