The giant-impact model suggests that, in the Earth's early history, the proto-Earth and Theia (a Mars-sized planet) collided and reformed as one body. A small part of the new mass spun off to become the Moon.
Some suggest that early Earth and Theia came from the same neighbourhood as the solar system was forming and were made of similar materials.
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If you look at the lunar surface, it seems pale grey with dark splodges.
The pale grey is a rock named anorthosite. It forms as molten rock cools down. The dark areas are another rock type called basalt. Basalt is the most common surface on all inner planets in our solar system and can be found on the ocean floor.
The Apollo mission brought back rock and soil from the Moon. It showed that the Earth and Moon share chemical and isotopic similarities, suggesting a linked history.
The minerals on the Moon contain less water than similar terrestrial rocks. The Moon has material that forms quickly at a high temperature.
Before the Apollo mission research, there were three theories about how the Moon formed.
Today, the giant-impact theory is widely accepted. It proposes that Earth and a small planet collided. The debris from this impact collected in orbit around Earth to form the Moon.
The smallest planet in our solar system and nearerst to the Sun,
Mecury is only slightly larger than the Earth's Moon. From the surface of Mercury, the sun would appear more than three times as large as it does when viewed from Earth, and the sunlight would be as much as seven times brighter.
Despite its proximity to the Sun, Mercury is not the hottest planet in our solar system – that title belongs to nearby Venus, thanks to its dense atmosphere.
Mercury is the fastest planet, zipping around the Sun every 88 Earth days.
Mercury is appropriately named for the swiftest of the ancient Roman gods.
Mars was named by the ancient Romans for their god of war because its reddish color was reminiscent of blood.
Other civilizations also named the planet for this attribute; for example, the Egyptians called it "Her Desher," meaning "the red one." Even today, it is frequently called the "Red Planet" because iron minerals in the Martian dirt oxidize, or rust, causing the surface to look red.