The moon is still puzzling us. It is the only natural satellite on Earth and is a hundred times closer to it than the next planet. Until the 1980s, scientists thought the moon was a large asteroid captured by Earth. Other experts maintain that both moon and earth were formed in primordial dust clouds of the solar system. Today the Giant-impact theory is the most likely hypothesis.
- Moon’s main features
- How did the Moon form?
- Why giant-impact is the prevailing theory of moon’s origin?
- Where did the asteroid that impacted Earth come from?
- Can the moon support life?
The Moon formed about 4.53 billion years ago. Galileo Galilei (1564-1642) was among the first people to point a telescope at it. In 1609 he saw highlands, seas and craters. The physicist, mathematician and astronomer revolutionized the then prevailing view that the moon had a smooth, perfect surface.
Many people have been unwilling to accept these amazing news for a long time. A little later, Galileo Galilei also made another discovery. He found that three small moons revolve around the planet Jupiter.
Through these discoveries with the telescope, he sided with the world view of Nicolaus Copernicus. The latter had recognized that the earth is not the center of the planetary system.
As a follower of Copernicus, Galileo Galilei the Inquisition brought him to trial. Although he was a believer, Galileo did not want to recant his knowledge. In 1633, however, he had to recant his theory in a spectacular process to avoid the stake.
His persistence made him a symbol in the struggle for a scientific worldview.
Moon’s main features
Moon’s characteristics are related to its origins. The moon is the closest celestial body to earth. The average distance between the moon and earth is around 384,400 km. Compared to Earth, however, the moon is significantly smaller. Its circumference is about 4 times smaller and it is 81 times lighter.
Due to its lower mass, moon’s gravity is also significantly weaker. Therefore, astronauts weigh only a sixth of their earth’s weight on the moon. This affects their locomotion in particular. They can jump six times higher on the moon, but they can also only run six times slower.
If you land on the moon, you will find a desolate desert landscape, which mainly consists of fine gray dust. During the day it is very hot, the stones can heat up to 110 degrees Celsius. At night, on the other hand, the temperature drops to minus 170 degrees Celsius within a few seconds.
The moon does not emit its own light. Basically, there is “moonlight” because it reflects sunlight. From earth you can only see the part illuminated by the Sun. Phases of the moon are the result of this reflection:
- New Moon
- Waxing Crescent
- First Quarter
- Waxing Gibbous
- Full
- Waning Gibbous
- Third Quarter
- Waning Crescent
- Dark Moon
How did the Moon form?
The giant-impact hypothesis (Theia Impact) is the prevailing theory of moon formation. According to this theory, an asteroid, roughly the size of Mars, collided with the still young earth around 4.5 billion years ago. The energy of the impact instantly heated the entire surface of the earth to more than 10,000 degrees Celsius.
The impact smashed the surfaces of both bodies. Trillions of tons of rock from the asteroid and the earth evaporated and were thrown into space. Part of it accumulated in earth’s orbit and clumped together relatively quickly – probably within a few ten thousand years – to form the earth’s moon.
Why giant-impact is the prevailing theory of moon’s origin?
Giant-impact theory is supported by a number of indications.
- The ratio of different oxygen isotopes in the moon and earth rock are very similar, which indicates a close relationship between the origin of the two.
- Scientists are also aware that Earth’s satellite has only a small iron core. At the time of moon’s formation, most of the iron had already settled in the center of the respective core. Only iron-poor mantle and crustal rock was evaporated and hurled into space. The iron core of the moon was probably created by later asteroid strikes.
- Finally, the heat from the asteroid impact could be responsible for the lack of volatile minerals such as zinc, potassium and phosphorus in the lunar rock. These substances have presumably escaped from the hot gas cloud that later formed the moon. That would explain the different composition of earth and moon rock.
After the impact of the asteroid, the structure of the earth changed radically. The core of the asteroid melted during the collision and was swallowed up by the earth. About 60 to 70 percent of the original earth’s crust was blown up into space – material that soon orbited the earth as a glowing ball. The glowing earth also quickly resumed spherical shape, so that all traces of the catastrophe were blurred.
Where did the asteroid that impacted Earth come from?
The researchers still know very little about the origin of the moon-forming asteroid. After all, computer simulations reveal that around 100 such giant asteroids and countless smaller ones flew through this part of space in the early days of the solar system. Through collisions and mergers, they formed the four planets closest to the sun, Mercury, Venus, Earth and Mars.
If the giant-impact theory is correct, the forming of Earth’s satellite would be a prime example of such a collision. A closer investigation could therefore provide information about the formation of other celestial bodies.
Can the moon support life?
Earth’s satellite must have had not only a dramatic birth, but also an extreme childhood. A viscous layer of magma covered the young moon for at least 100 million years. Heavy minerals containing iron and magnesium sank in it, lighter ones rose and formed a first crust – a forerunner of the bright moon surfaces.
Hail of meteorites smashed this crust, and as a result the first seas filled with dark magma from inside the moon. Thus, the dark spots (maria, from the Latin word for sea) of the moon were formed.
Then the cosmic fire of creation slowly subsided. But around 4 billion years ago, another long-lasting fire must have broken out over the lunar landscape.
Presumably the primeval forms of life developed on Earth. It is unclear what influence the meteorite fire had on it. This question is one of the greatest mysteries that moon research could solve. Some researchers even hope to discover fossils of earlier life forms on the moon.
The Indian lunar probe Chandrayaan-1 achieved the greatest success in 2009. It found large amounts of water on the lunar surface that could be used to supply manned lunar missions in the future.
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