La planète Mercure et le soleil

What is the closest planet to the sun?


Our distance from the sun seems perfect, because the warmth it gives us is conducive to life. Indeed, if on Earth, we complain about heat waves, it is a completely different atmosphere on Mercury, the planet closest to the sun.

The planet Mercury

Identified since the highest antiquity, by the Assyrians, as early as the 20th century BC, Mercury is a very fast and very bright wandering starobservable with the naked eye before dawn and after dusk. That’s why the Romans called it Mercurythe name of messenger of the gods.

How far from the Sun is Mercury?

Of all the eight major planets that make up our solar system, Mercury is closest to the sun. It is located 0.39 AU from the latter, which corresponds to 59 million kilometers medium distance.

She is too the smallest of all the planets. Its diameter is only 4,879.4 kmthat is 3 times smaller than the Earth.

Its formation dates from 4.5 billion years oldor from the very 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 scattered Where destroy considerable amounts of material. This explains the thinness of the outer layer of the planet. Simulations on the formation of planets have shown that it took 4 million years for 50% of these current particles fall back on Mercury.

The planet Mercury in black and white

physical properties


Like all telluric planetsMercury has three concentric solid and liquid envelopes including:

  • A standard metal core very dense, occupying nearly 42% of its volume, 70% of its total mass. It represents 85% of the radius of the planet which corresponds approximately to 2025km.
  • A molten mantle layer of 200 kilometers inside a rocky mantle of 600 kilometers a merger.
  • A solid crust of 35 to 54km covering the mantle.

Its surface is very similar to the far side of the moon. Indeed, it is riddled with craters resulting from violent meteorite falls. Let us mention in particular the Heat Basinwhich 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.

It can be clearly noticed a huge flaw on its surface. Scientists believe this is due to the cooling of its continental crust. Because of this, his ray experienced a decrease of about 7 km following this phenomenon.

The planet Mercury

Atmosphere and climate

At first glance, Mercury appears dry and without atmosphere, but it is not. The probes sent by the Nasa in particular, were able to detect a modest proportion of hydrogen, helium and oxygen. Moreover, water vapor has also been listed, as well as sodium, calcium and potassium. Which leads them to think that its atmosphere is in continual renewal.

In fact, his original atmosphere was dispersed soon after its formation. Moreover, the heat, the low gravity of the planet and the major action of the solar wind make Mercury impossible to maintain a meaningful atmosphere. It also justifies huge temperature differences on its surface. At the zenith, when the sun is closest to perihelion, it can reach extremes of 420°C. Conversely, it can reach -175°C in the shade.

Furthermore, we found ice at the poles at the bottom of craters 5 km deep and with 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?


orbit of Mercury, of form elliptical, is the most out of the way of the solar system. Its distance from 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 during 88 earth days only. Thereby, a year on Mercury thus corresponds to approximately 3 months on earth.

In contrast, it turns on itself more slowly because of its rotation period. A day on Mercury corresponds approximately to 59 earth days in principle, approximately 2 months.

The perihelion

Johannes Kepler repeats the observations of Tycho Brahe . Thus, it shows that the planet Mars crossed an elliptical orbit with variable speed.

He deduces that the distance from the sun can change. Because of this, the planets go faster near the Sun and slow down as they move away.

In 1965 it was discovered a particularity at Mercury. Like what, approaching the perihelion, orbital velocity is acceleratingthe planet at some point exceeds its rotational speed and the sun rises there twice a day.

In other words, a full mercurian day lasts for two orbits around the sun (two mercurian years). In addition, she performs 3 turns on itself, that is, approximately 176 earth days.

Newton, he found that the perihelion of Mercury move in time. According to him, it advances with an approximate period of 225,000 years and constantly changing position. This stems largely from the influence of nearby planets : Jupiter, Venus, Earth.

This is Albert Einstein then who clarifies the reason for this phenomenon. In his theory, he explains that it is the colossal mass of the sun who bends space-timethus influencing the movement of the perihelion of Mercury. However, it was in 1915 that we were able to prove this postulate.

The transit of Mercury

Namely that the plane of Mercury’s orbit is inclined at 7° on that of the earth. This is the reason why this rare phenomenon takes place every 23 Mercurian years on average. Thus, the transit of Mercury occurs when it passes between the sun and the earth. It is visible in the form of a black point which crosses the solar disc. Mercury’s last transit was on November 11, 2019 and the next will be on November 13, 2032.

Space missions on Mercury

In 1974, the space probe SAILOR 10 of Nasa brings us the first images of the surface of Mercury. During its launch in orbit towards Venus, it is programmed to pass close to Mercury every 2 Mercurian years.

In 2004, a more sophisticated probe called MESSENGER is launched for a orbit around Mercury. However, due to the presence of the sun, regular orbit corrections are made for years before reaching the goal.

It’s only by 2011 that the probe finally arrives at its destination. That said, it flew over the planet at a minimum altitude of 200 km and a maximum altitude of 15,200 km. His mission lasts 4 years and ends in 2015.

In 2025, the probe BepiColombo of the’ESA/JAXA launched in October 2018 should orbit Mercury. Its purpose is to study the planet and its magnetosphere for 2 years.

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