Today we continue with the journey in our solar system, but we won't talk about a planet. We are going to discover our satellite: the Moon.
The Moon, photo by NASA
Still today, there is some uncertainty on the origin of the Moon, but we are quite confident in discarding the hypothesis that it was originated by detaching from Earth, in particular from the Pacific crust. This is only two hundred million years old and, as we saw in the last number, it was modeled by the continental drift, without any sign of a detached body. Moreover, the chemical composition of the Moon is quite different from the one you could find somewhere on Earth. A recent suggestion is that Moon formed in the protoplanetary stages of Earth itself, when a collision with a celestial body with similar dimensions of Mars, caused a massive ejection of material. After that event, gravity did the job.
As you may know, it is the only Earth's natural satellite and its orbit has a mean radius of 384,000 kilometers, being almost circular. Very interestingly, Earth and Moon are tidally locked. Their rotations are so syncronized that we only see one side of the Moon independently from where on Earth we are looking. Indeed Moon needs the same time both to rotate around its axis and around our planet and humans didn't see the lunar far side until a Soviet spacecraft flew past it in 1959! Today, more than 105 robotic spacecraft have been launched to explore and it is the only celestial body beyond Earth visited by human beings, so far.
By looking directly from Earth, dark and light areas are visible without the need of a telescope. Therefore, humans have always been able to observe the Moon with a high enough level of detail and called the lighter regions 'seas', these areas are in fact uplands; if you were wondering, there is no liquid water on the Moon, even if some water ice has been found near the South Pole.
All the observed craters are meteorite impacts, even though there is quite an active tectonic activity: the 'Moonquakes', which help to better understand the underground structure of the satellite.
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The SpaceInfo Team
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