Earth and Moon
Earth
Earth is the third closest planet to the Sun, orbiting once about every three hundred and sixty five days. It is larger, denser and more massive than Mercury, Venus and Mars and has one natural satellite, the Moon. Earth formed into a fully molten state about four and a half billion years ago and life evolved on its surface within a billion years. The Earth is the only place in the universe where life is known to exist and almost all life on Earth is fuelled by energy from the Sun. It takes light just over eight minutes to travel to Earth across a distance of about a hundred and fifty million kilometres. This distance is defined as one Astronomical Unit (AU).
Over seventy percent of the surface of the Earth is covered with salt-water oceans, the rest is composed of continents and islands. The interior of the Earth contains a thick layer of solid mantle, a liquid outer core which generates a magnetic field, and a solid inner core of iron. Earth's axis is tilted at 23.4 degrees and this is responsible for the seasons.
The Star Garden
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Apollo 8 view of Earth and Moon, Earth & The Indian Ocean
At the time of its formation, the Earth had an atmosphere of carbon dioxide, nitrogen, methane and sulphur. During the next five hundred million years the surface was bombarded with comets which brought water and a cocktail of other elements and molecules. Almost three billion year ago, plants began photosynthesising, and the atmosphere filled with nitrogen and oxygen. Carbon dioxide formed a thick layer in the upper atmosphere, trapping the light of the Sun so that the surface did not freeze. The average temperature of the Earth is currently rising because of the increase in greenhouse gases released into the atmosphere since the industrial revolution. As the temperature increases, glaciers will melt and there will be more extreme weather events such as droughts and heavy rainfall. Many species will be wiped out and lands will become infertile. It is hoped that human intervention can prevent this from happening.
Bruce McCandless II above the Earth Mark C. Lee above the Earth
Moon
The Moon is the Earth's only natural satellite and at over three thousand kilometres wide, it is a quarter the size of the Earth. It is currently accepted that when the Solar System was still forming, about four and a half billion years ago, the Earth and Moon were part of the same gravitationally bound mass. This was hit by an object the size of Mars, which scraped the outside off. This layer broke away and fell together again to make the Moon.
The Moon crashed into hundreds of tiny rocks as it was flung from the Earth, covering its surface with craters. Just as this bombardment was coming to an end several large objects hit the newly formed surface, blowing away the white soil on the near side and releasing dark lava which filled the craters, creating the Moon's seas.
The Moon is not massive enough to be able to retain an atmosphere. As it solidified, the small amount of iron that it contains sunk to the centre. This is now surrounded by a mantle and then a fifty kilometre crust composed of oxygen, silicon, magnesium, iron, calcium, and aluminum. In 2009, at least one hundred kilograms of water were found on the Moon. The Moon is now almost four hundred thousand kilometres from the Earth. Its rotation and orbital periods are both about a month long and so the same side always faces us.
In 1959, the Soviet's Luna 2 was the first spacecraft to reach the Moon's surface, crashing into the surface east of Mare Serenitatis, the Sea of Serenity. That same year, Luna 3 was the first to photograph the dark side of the Moon. They found the surface to be mountainous, covered with large boulders and lots of small craters. The Soviet Union were the first to successfully land a spacecraft on the Moon in 1966 when Luna 9 touched down in the Oceanus Procellarum, the Ocean of Storms. NASA's Surveyor 1 made a successful landing four months later. Twelve people have walked on the Moon, all between 1969 and 1972. Russia, Europe, Japan, China, and India have all stated that they would like to complete a manned mission to the Moon within the next century and in 2005, NASA promised that America would return people to the Moon by 2018.
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