Despite the fact that we're able to send probes far out into the universe, we still don't know how our own Moon was created. Astrophysicist Dr. Robin Canup has a new theory?he says the Moon was created in a double impact 4.5 billion years ago, which destroyed almost all of the Earth as it existed then. A young planet that was almost our twin hit the Earth not just once, but twice. The Earth re-formed, but the debris from the impacting planet became our Moon.
According to Canup, a young planet that was still being formed and was about the size of Mars collided at high speed with Earth. The collision shattered Earth and destroyed the incoming planet, turning it into a shower of debris. But within hours, much of this re-grouped to form a new impactor that smashed into the Earth's surface a second time!
"At this point, the impacting object was destroyed," says Camp. Most of the impactor debris rained down on Earth after the second hit and became incorporated into it. But about 10% of the mass remained in a cloud around the Earth, like one of Saturn's rings.
During the next few decades, this ring formed the Moon. "At the time it was 15 times closer than the Moon is now," says Canup. "So if you had been able to stand on the surface of the Earth then, you would have seen something that appeared 15 times the size of what even today is an impressive full Moon."
Recent research shows that the planet that collided with Earth was almost its twin chemically. Scientists have named it "Theia" after the mother of the Moon in Greek mythology. The Moon was originally thought to have been a satellite that was captured by Earth's gravity. When astronauts went to the Moon and brought back Moon rocks, they found they were identical to rocks on the Earth, so it was then thought that a meteor knocked off a piece of the Earth, which then became the Moon. Now we know that the Moon was made from another planet entirely?one that was chemically almost identical to Earth.
The impact gave us the Moon which protects us from impacts from space (as does Jupiter) and from the harsh winds that would otherwise blow constantly across our surface. It also set the Earth spinning on its axis, so we have 24-hour days. Theia was a twin that gave up its existence so the Earth could have life.
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