What is the closest planet to the sun?

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La planète Mercure et le soleil

Our distance from the sun seems perfect, because the heat it provides us is conducive to life. In fact, if on Earth, we complain about heat waves, it is a completely different atmosphere on Mercury, the planet closest to the sun. Identified from the earliest times, by the Assyrians, from the 20th century BC, Mercury is a very fast and very bright wandering star, observable with the naked eye before dawn and after sunset. That is why the Romans called him Mercury, the name of the messenger of the gods. How far is Mercury from the Sun? Of the eight main planets that make up our solar system, Mercury is the closest to the sun. It is 0.39 AU from the latter, which corresponds to an average distance of 59 million km. It is also the smallest of all the planets. Its diameter is only 4,879.4 km, or 3 times smaller than Earth. Its formation dates back to 4.5 billion years, from the beginning of the solar system. Scientists believe it is the result of the collision of a giant asteroid and a protoplanet. During this event, solar radiation dispersed or destroyed considerable amounts of material. This explains the thinness of the outer layer of the planet. Simulations of planet formation have shown that it took 4 million years for 50% of these present-day particles to fall on Mercury. Physical Properties Composition Like all terrestrial planets, Mercury has three concentric solid and liquid envelopes that include: A huge and very dense metallic core, which occupies almost 42% of its volume, 70% of its total mass . It represents 85% of the radius of the planet, which corresponds to about 2025 km. A layer of 200 km of molten mantle inside a molten rocky mantle of 600 km. the layer. Its surface is very similar to the end of the moon. In fact, it is full of craters resulting from the violent falls of meteorites. Among these, the Caloris basin stands out, which measures approximately 1,300 km in diameter. It is the trace of a collision with an asteroid 150 km in size, 3.85 billion years ago. A large defect can be clearly noticed on its surface. Scientists believe this is due to the cooling of its continental crust. Therefore, its radius experienced a decrease of about 7 km as a result of this phenomenon. Atmosphere and Climate At first glance, Mercury appears dry and without an atmosphere, but it is not. In particular, probes sent by NASA were able to detect a modest proportion of hydrogen, helium and oxygen. In addition, water vapor has also been listed, as well as sodium, calcium and potassium. Which leads them to think that their environment is in continuous renewal. In fact, its original atmosphere dispersed shortly after its formation. In addition, the planet’s heat, low gravity, and strong solar wind action make it impossible for Mercury to maintain a significant atmosphere. This also justifies the large temperature differences on its surface. At Zenith, when the Sun is closest to perihelion, it can reach extremes of 420°C. Conversely, it can reach -175 °C in the shade. In addition, ice was found at the bottom poles of craters 5 km deep and at a temperature of -200°C. This can be explained by the fact that these places are never exposed to the sun. SEE ALSO: How many planets are there in the solar system? How to count the days on Mercury? The orbit The elliptical orbit of Mercury is the farthest from the solar system. Its distance to the sun varies by 40%. This figure is equivalent to 46 million km to 70 million km from the sun during its revolution. She undertakes this journey for only 88 Earth days. Therefore, a year on Mercury corresponds to approximately 3 months on Earth. On the other hand, it rotates on itself more slowly due to its rotation period. One day on Mercury corresponds to approximately 59 Earth days in principle, or approximately 2 months. Perihelion Johannes Kepler takes up the observations of Tycho Brahé. Thus, it shows that the planet Mars crossed an elliptical orbit with variable speed. Deduce that the distance to the sun can change. Because of this, the planets go faster near the Sun and move further away as they move away. In 1965, a peculiarity was discovered on Mercury. As it approaches perihelion, the orbital speed accelerates, the planet exceeds its rotation speed at some point, and the sun rises there twice a day. In other words, a full Mercurian day lasts two orbits around the sun (two Mercurian years). In addition, it makes 3 revolutions on itself, or approximately 176 Earth days. Newton observed that the perihelion of Mercury moves in time. According to him, it advances with an approximate period of 225,000 years and constantly changes position. This comes largely from the influence of nearby planets: Jupiter, Venus, Earth. It was then Albert Einstein who clarified the reason for this phenomenon. In his theory, he explains that it is the colossal mass of the sun that causes space-time to bend, thus influencing the motion of Mercury’s perihelion. However, it was in 1915 that we were able to prove this postulate. The transit of Mercury That is to say, that the plane of Mercury’s orbit is inclined 7° with respect to that of the earth. This is the reason why this rare phenomenon takes place on average every 23 Mercurian years. Thus, the transit of Mercury occurs when it passes between the sun and the earth. It is visible as a black dot crossing the solar disk. The last transit of Mercury took place on November 11, 2019, and the next one will be on November 13, 2032. Space missions to Mercury In 1974, NASA’s MARINER 10 space probe brought us the first images of the surface of Mercury. During its launch into orbit towards Venus, it is scheduled to pass close to Mercury every 2 Mercurian years. In 2004, a more sophisticated probe called MESSENGER was put into orbit around Mercury. However, due to the presence of the sun, regular orbit corrections are made for years before reaching the target. It wasn’t until 2011 that the probe finally reached its destination. That said, it flew over the planet at a minimum altitude of 200 km and a maximum altitude of 15,200 km. Its mission lasts 4 years and ends in 2015. In 2025, the BepiColombo ESA/JAXA probe launched in October 2018 should enter orbit around Mercury. Its purpose is to study the planet and its magnetosphere for 2 years.
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