Mercury is the planet closest to the Sun and is one of the four solid and rocky planets called “inner planets“: Mercury, Venus, Earth, Mars.

The cover image shows Mercury the Planet Closest to the Sun. Credit: web “”

planets size Credit: web “”

Mercury is the smallest of the four Planets of the image, with a diameter of 4,879 km at the equator.

In the image, you can see the size of Mercury compared to Earth.

The apparent magnitude of Mercury ranges from -2.0 (bright like the star Sirius) to 5.5.

Mercury Earth
The Earth and Mercury  Credit: web “”

Mercury physical characteristics

Planet Mercury is made up of approximately 70% metallic elements and 30% silicates.

The density of this planet is the second largest in the entire solar system, only slightly smaller than the density of Earth.

Mercury has no satellites.

The latest observations carried out, suggest the existence of water ice at the bottom of several very deep.

Also it shows dark craters, near the poles, which have never been directly exposed to sunlight.

Water ice is highly reflective to radar; It is speculated that the ice covers only a few meters of depth of these craters, and that they contain about a ton of this substance.

The origin of the ice water on Mercury is not known for sure, but it is speculated that it either condensed from water inside the planet or came from comets that hit the ground.

Sodium has been discovered in abundance in a kind of tail that extends almost 40,000 km away from the Sun.

The orbit of Mercury

The orbit of Mercury is the most eccentric of the minor planets.

Its distance from the Sun is in a range of between 46 million and 70 million kilometers.

Mercury takes 88 Earth days to make a complete translation around the Sun.

Orbits planets
Orbits of the sun’s Planets  Credit: web “”

The orbital inclination with respect to the plane of the ecliptic is 0.01º. That of Jupiter is 3.1º and that of Earth is 23.5º.

An observer at Mercury’s equator at local noon would never see the Sun more than 0.01 ° north or south of the zenith.

Similarly, at the poles the Sun never passes 0.01º above the horizon.

Mercury transit

Being a planet whose orbit is interior to that of the Earth, Mercury periodically passes in front of the Sun.

The Earth crosses the line of the nodes of Mercury’s orbit each year on May 8-9 and November 10-11.

If on those dates the three stars (Sun, Earth, Mercury) are aligned, from the Earth the curious fact is observed that Mercury passes in front of the Sun.

This is called “transit.” Something similar happens with the Venus planet.

Mercury Sun
Mercury passing in front of the Sun in 2006 Credit: web “”

There is a certain periodicity in these phenomena although it obeys complex rules. Mercury tends to transit in front of the solar disk on average about 13 times per century at intervals of 3, 7, 10 and 13 years.

Other characteristics of Mercury

It is estimated that the core of Mercury occupies 42% of the total volume of the planet (the core of the Earth only occupies 17%) and that it is very rich in iron.

The study of the interaction of Mercury with the solar wind revealed the existence of a magnetic field around the planet.

In 2007, some very precise observations made from Earth by radar, showed a wobble in the axis of rotation of Mercury.

The only reasonable explanation would be that the core was partially molten and that it consisted of ferric materials, which would be the cause of its magnetic field.

Mercury has Inner Solid Core web “solarsystem.nasa.gob”

Surrounding the nucleus there is a mantle about 600 km thick.

The general belief among experts is that in the early days of Mercury, a body several kilometers in diameter impacted on it, breaking up most of the original mantle, resulting in a relatively thin mantle compared to the large core.

The crust is around 200 km thick. A distinctive feature of Mercury’s crust is the many rugged lines that stretch several thousand kilometers across the planet.

Mercury Craters

The surface of Mercury, like that of the Moon, suffered a period of intense bombardment by large meteorites, about 4 billion years ago.

Mercury craters
Mercury photo obtained by Mariner 10. Credit: web “” author: Leonid Ksanfomality

Mercury received impacts on its entire surface, facilitated by the absence of an atmosphere that could disintegrate or slow down many of these rocks.

Some of the craters are relatively recent, a few million years old, and are characterized by the presence of a central peak.

The oldest craters have had a more prolonged erosion, possibly due to large changes in temperature that on a normal day range between 350º C during the day and –170º C at night.

The surface of Mercury

The plains of Mercury have two different ages; the young plains have fewer craters and were probably formed when lava flows buried the old terrain.

A characteristic feature of the surface of this planet is the many folds that criss-cross the plains.

It is thought that when the interior of the planet cooled, it contracted and this caused the deformation of the surface.

These folds can be seen above craters and plains, indicating that they are much more recent.

The surface of Mercury is significantly flexed to cause of the tidal forces exerted by the Sun, which are 17% stronger than those exerted by the Moon on Earth.

The Caloris Basin

In the geology of Mercury, the Caloris Basin stands out, an impact crater that constitutes one of the largest meteoric depressions in the entire solar System.

It has an approximate diameter of 1,550 km with an albedo greater than that of the surrounding terrain (contrary to what happens on the Moon).

A close-up view of Mercury. Credit: Jennifer Chu, MIT News Office, web “”

It also contains an unobserved formation on the Moon, consisting of approximately one hundred narrow, smooth-ground fissures known as La Araña; in the center of it is a crater.

In the antipodes of the Caloris Basin there are hills or mountain ranges known as Strange Territory.

One hypothesis about the origin of this geomorphological complex is that the shock waves generated by the impact that formed the Caloris Basin crossed the entire planetary sphere, converging on the opposite end of the planet, fracturing the surface and forming this mountain range.

Mercury The Caloris Basin Credit: web “”

The surface of Mercury has probably suffered the effects of processes of space erosion, caused by the solar wind and the impacts of micro meteorites.

Mercury atmosphere

The Mariner 10 probe demonstrated the existence of a very thin atmosphere, consisting mainly of potassium and sodium, and which has a pressure of only one hundred thousandth of the atmospheric pressure at the surface of the Earth.

Mariner 10
Mariner 10 was the space probe launched by NASA on November 3, 1973  Credit: Wikipedia, NASA

This very light atmosphere is explained by the fact that since Mercury is a very small planet, its gravitational attraction is insufficient to retain a higher atmospheric density for long periods of time.

This atmosphere is lost, escaping into space and is being replaced by hydrogen and helium atoms that come from the solar wind and that are diffused in the magnetosphere.

Visual observation of Mercury

It’s not easy to see Mercury by its proximity to the Sun.

Marcury can only be observed for a short period of time shortly before sunrise or during evening twilight.

It is easier to see from the southern hemisphere of the Earth than from the northern hemisphere.

In both cases, it is seen to rise several hours before the Sun and does not set until several hours after sunset, in countries located in temperate latitudes of the southern hemisphere, such as Argentina and New Zealand.

Like many other bright stars and planets, it can be seen during a solar eclipse.

Mercury is also brightest seen from Earth when it is between the waxing or waning phase and filling it up.

Unlike Venus, when it appears brightest it is in a crescent quarter, because it is when it is closest to the Earth.

Is there ice water on the planet Mercury?

In 2004, NASA launched the Messenger probe into space and on March 18, 2011,.

Technicians managed to place it in a highly elliptical orbit that ranges from 200 kilometers to 15,000 kilometers from the surface of Mercury.

The finding reported is that the mapping carried out by the Messenger probe has verified that there are polar regions of permanent shadow that support the hypothesis about the existence of wáter.

Eight planets
Eight planets of the solar system Credit: Wikipedia