Earth may have had two moons

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Earth may have had two moons — one visible today and the other a smaller twin, according to scientists.
The second moon was destroyed in a collision with the present moon and lasted for only a few million years, according to Prof. Erik Asphaug of the University of California, who will unveil his two-moon theory at a scientific discussion on the origin of moon at the Royal Society in London in the last week of September.
The Earth and moon are thought to have been formed between 30 million and 130 million years after the birth of the solar system, about 4.6 billion years ago. There are an estimated 100 billion planets like Earth in the Milky Way galaxy.
The second moon would have formed early in Earth’s history from the same giant impact thought to have given rise to the surviving moon, Prof. Asphaug told the Sunday Times. “The second moon would have lasted for only a few million years; then it would have collided with the moon to leave the one large body we see today,” he said.
Landscapes on the moon are the remains of the smaller moon from the collision. “It would have orbited Earth at the same speed and distance and just got slowly sucked in until they hit and then coalesced,” he said.
In an earlier study, published in the Nature, Prof. Asphaug had revealed that the companion moon was initially trapped at one of the gravitationally stable “trojan points” sharing the moon’s orbit, and became destabilized after the moon’s orbit had expanded far from Earth.
He had put forward the hypothesis that the mountainous region on the far side of the moon, known as the lunar farside highlands, could be the solid remains of a collision with a smaller companion moon.
Scientists believe that the inner solar system at one time may have had up to 20 planet-sized bodies which collided into each other until only eight remained.
Last year, scientists in the Harvard University put forward a theory in a study published in the journal Science suggesting that the moon was once part of Earth that spun off after they collided with another body.