Moon - Formation, structure and facts - Information For kids
This hub gives detailed information on the formation of the moon, the different theories involved in the formation of the moon, the structure of the moon and some interesting facts about the moon.
We all live on a planet called Earth. Did you know that the Earth had a satellite called the Moon? Yes, it is the Earth’s natural satellite and is the fifth largest satellite in the solar system and the biggest satellite to a planet in the Solar system. It orbits around the earth once every 27.3 days and it has its same side facing the earth at all times. The average distance between the moon and the earth is 384,400kms. In this hub we will look at how the moon was formed, the structure of the moon and other characteristics of the moon.
The Moon is a satellite that resembles a planet also called "The light that rules the night". It is almost one quarter of earth’s diameter and its gravity is just one sixth of the earth’s gravity because of its relatively small size as compared to Earth. The density of the moon is relatively low compared to the earth because of its small iron core. There is very less volatile substances in moon, which confirm the high baking surface of the moon. The identical oxygen isotopes suggest that the earth and the moon formed at relatively similar distances from the sun. The moon is believed to have formed 4.5 billion years ago, and there are a few theories behind as to how the moon was formed.
The fission hypothesis or theory, as the name explains, where the moon was formed as a result of simply breaking off from earth and it is believed that a basin in the Pacific Ocean is a proof for that, although it is very much younger compared to the age of the moon.
Lunar capture or the capture theory, again as the name explains, says that the moon which was somewhere far away from the earth was captured as a result of earth’s gravitational field.
Co-accretion theory or co-creation theory, that states that the earth and the moon were formed of similar building blocks in the same part of the solar system, but does not account for the fact that moon has very less iron content compared to earth.
Birth of the Moon
The giant impact or the ejected ring theory is the theory that is believed to be true at the moment. According to this theory, the earth which was still young around 4.5 billion years ago, was collided by a planetary object, roughly the size of Mars and this Giant collision released large amount of debris from the mantle of the earth into the earth’s orbit, which was enough for the moon to form, and hence the reason why moon has far lower percentage of iron.
The Structure of the moon:
Very similar to the structure of the earth, the moon has the crust, the mantle and the core, which are believed to have formed as a result of the fractional crystallization of magma after its formation around 4.5 billion years before. The moon’s diameter is roughly 3474kms
The moon’s crust is anorthositic in nature. According to a science dictionary, Anorthosite means an igneous rock consisting almost entirely of plagioclase feldspar, especially the labradorite variety, and these have been identified among the rock samples collected from the moon. The crust contains minerals like, oxygen, silicon, magnesium, iron, calcium and aluminium. Also traces of titanium, uranium, thorium, potassium and hydrogen are present. The thickness of the crust is between 50 km and 65 km.
The mantle is divided into upper mantle, middle mantle and lower mantle. It has larger iron content than earth’s mantle. Moon-quakes are believed to occur in the moon’s lower mantle periodically due to tidal effects between the earth and the moon. The mantle is between 800 – 1000kms thick. The lower mantle is partially fluid and contributes to the moon-quakes which can erupt on the lunar surface.
The core is just 20% of the size of the moon, which leads to its lower density and gravitational field. It is believed that the lunar core is metallic iron in its alloyed state with traces of sulphur and nickel. The core has two layers, the solid inner core which is about 160kms in radius and the fluid outer core which is about 350kms in radius. The complete core works out to be around 500kms in radius.
The moon has basically 2 different types of terrains, the Maria and the highlands. Besides these there are other features like the rilles, domes, wrinkle ridges, grabens, impact craters, regolith, lava tubes etc.
The Maria is the dark-coloured regions we see on the moon. These are lowland basins and they cover 15% of the moon’s surface, which is almost a third of the side facing the moon. These are mostly found on the side of the moon facing the earth which is also called the near-side of the moon. These are less cratered and are believed to be filled in by flows of lava as they have patterns similar to lava flow. There are also dark mantle deposits, which form part of the Maria region. These are pretty younger regions when compared to the highlands, and are mostly composed of basalt.
The highlands cover almost 85% of the lunar surface and are heavily cratered. They are very ancient regions when compared to the Maria. These are anorthositic in nature. The far-side or the side of the moon away from the earth is very similar to these highlands area, and are heavily cratered.
The Moon for Kids
The phases of the moon:
When you watch the moon over a month’s time, you can see that it has different phases. The moon does not have any light of its own, and it reflects the light from the sun falling on it. Since the moon rotates or orbits around the earth, it reflects different amounts of light, depending on its position relative to the sun. These are called the phases of the moon.
On occasions, the moon passes between the earth and the sun, thereby causing a solar eclipse, and also when the moon passes directly behind the earth away from the sun, it causes a lunar eclipse. During a Lunar eclipse, the moon is reddish orange in colour and this is due to the limited rays from the sun and rays diffracted around the edge of the earth that fall on the moon.
The volcanic activities due to moon quakes on the moon are responsible for the Maria, which are low lying regions where the lava flows into. There has been no evidence of tectonic movements on the lunar landscape as compared to the ones on earth.
There are roughly 300,000 big craters wider than 1 km found on the near side surface of the moon and these are believed to have formed due to the impact of comets and asteroids on the surface of the moon. Due to extreme temperatures on the surface of the moon, water will quickly decompose off due to solar radiation. However on the side of the moon which is permanently dark, and where there are no solar radiation for example the poles, there can be water ice, which would have been deposited by comets or produced by the reaction of lunar rocks which are rich in oxygen, and hydrogen from the solar wind.
Some interesting facts about the moon:
- The moon has a very small magnetic field compared to that of earth’s. Its gravity is too low as compared to the earth, as due to the reasons discussed earlier.
- The mass of the moon is 7.35 x 1022 kg, which is roughly 0.0123 times the mass of the earth.
- The density of the moon is 3.34 gm/cm3 which is roughly 0.6 times the density of earth.
- The surface temperature of the moon can vary between 204o C during the day to -205o C during the nights.
- The moon has no atmosphere, which means no sound can be heard and the sky is dark all the time due to no scattering or dispersion of light.
- The rise and fall of ocean tides on earth is due to the gravitational pull of the moon on the earth.
- The moon’s orbit around the earth is an ellipse
- For the moon to complete its phases once, takes 29.5 days and that is called one Lunar month.
- The moon orbits around the earth at a speed of 3683 kms/hour
- The moon has no wind or weather, because it has no atmosphere and hence the footprints left by astronauts will stay there for millions of years.
- The full moon has different names as to which month it occurs.
- The moon is the only extra-terrestrial body that has ever been visited by humans.