What is the closest planet to the sun?

Our distance from the sun seems perfect because the heat it gives 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 since the highest antiquity, by the Assyrians, as early as the 20th century BC, Mercury is a very fast and very bright wandering star, can be observed 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 is closest to the sun. It lies 0.39 AU from the latter, which corresponds to 59 million km middle distance.

So is she the smallest of all the planets. Its diameter is only 4,879.4 kmit is 3 times smaller than Earth.

Its formation originates from 4.5 billion years old, or from the very beginning of the solar system. Scientists believe it is the result of the collision between a giant asteroid and a protoplanet.

During this event, solar radiation scattered Where destroy significant amounts of material. This explains the thinness of the outer layer of the planet. Simulations of the formation of planets have shown that it took 4 million years for 50% of these present particles fall back on Mercury.

The planet Mercury in black and white

physical properties


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

  • A standard Metal core very dense, occupying almost 42% of its volume, 70% of its total mass. It represents 85% of the planet’s radius, which corresponds to approx 2025 km.
  • A melted mantle layer off 200 km inside a rocky mantle of 600 km in fusion.
  • A solid crust of 35 to 54 km covers the mantle.

Its surface is very similar to the other side of the moon. It is actually filled with craters as a result of violent the meteorite falls. Let us mention in particular The Caloris Basinwhich measures approx 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 felt a major flaw on the surface. Scientists believe that this is due to the cooling of its continental crust. Because of this, his beam experienced a drop of about 7 km after this phenomenon.

The planet Mercury

Atmosphere and climate

At first glance, Mercury appears dry and without an atmosphere, but it is not. The probes sent by NASA in particular was 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 makes them think its atmosphere is in continuous renewal.

Actually his original atmosphere was dispersed shortly after its formation. In addition, the heat, the planet’s low gravity and the great influence of the solar wind make Mercury impossible to maintain a meaningful atmosphere. It also warrants large 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 shadow.

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 do you 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 below its revolution.

She undertakes this journey under 88 earthly days only. Thereby, one year on Mercury therefore corresponds to approx 3 months on earth.

Opposite to, it turns itself on slower due to its rotation period. One day on Mercury corresponds to approx 59 earthly days in principle approx Two months.


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

He infers that the distance from the sun can change. Because of this, the planets speed up near the Sun and slow down as they move away.

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

In other words, a full mercury day goods for two orbits around the sun (two mercurian years). In addition, she performs 3 rounds on itself, so approximately 176 earth days.

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

This is Albert Einstein who then clarify the cause of this phenomenon. In his theory, he explains that it is the colossal mass of the sun WHO bends space-time, thereby affecting the motion of Mercury’s perihelion. However, it was in 1915 that we were able to prove this postulate.

Transit of Mercury

Namely that the plane of Mercury’s orbit is inclined 7° on earth. This is why this rare phenomenon occurs every 23 Mercury years on average. 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. Mercury’s last transit was on November 11, 2019 and the next one will be on November 13, 2032.

Space missions on Mercury

In 1974, the space probe NAVY 10 of NASA brings us first images of Mercury’s surface. During its launch into orbit towards Venus, it is programmed to pass close to Mercury every 2 Mercury years.

In 2004, a more sophisticated probe rang 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 target.

It’s only at 2011 that the probe finally reaches 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’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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