Mercury; Everything you need to know about the closest world to the Sun

Mercury is the closest planet to the sun and the smallest planet in the entire solar system. This small, hollow planet has no moons and orbits the Sun faster than any other body. After Earth, Mercury has the highest density in the solar system and the diameter of its huge metallic core is between 3,600 and 3,800 km or 75% of the diameter of the entire planet. In contrast, the thickness of the outer shell of Mercury reaches 500 to 600 meters. The heavy core and composition of this planet, which contains a large amount of volatile elements, has become a puzzling mystery to scientists.

Years after the beginning of the space age, there is still much debate about how planets formed, and scientists are still not sure how they formed. The first and most important accepted theory is the core accretion theory, which is close to reality in the case of rocky planets like Mercury. The second theory, disk instability, applies to gas planets.

Approximately 6.4 billion years ago, the solar system was a cloud of gas and dust called the solar nebula. Gravity led to the collapse of materials and their rapid rotation. Thus, the sun was formed in the center of this nebula. With the formation of the sun, the rest of the material condensed. The smaller particles joined each other due to the force of gravity and turned into larger particles. The solar wind swept away the lighter particles, leaving only the heavy, rocky material near the Sun to form rocky planets like Mercury.

Like Earth, Mercury’s metallic core formed first, and then lighter elements formed its mantle and crust. Based on the observations of outer planets, the theory of core accumulation can be considered the dominant theory of the formation of rocky planets. One of the most accepted theories about the formation of Mercury is that in the early history of the solar system, an asteroid with 1/6 the mass of Mercury and a diameter of several thousand kilometers collided with it. has done. This collision has removed much of Mercury’s crust and mantle, leaving its core as the main element. A similar process known as the massive impact hypothesis has been proposed for the formation of the moon.

According to another theory, before the Sun’s energy output stabilized early in its life, the planet Mercury probably formed from the solar nebula. In the beginning, the mass of the planet Mercury was twice the current mass, but due to the high temperatures of the early sun, a large part of the surface rocks of Mercury evaporated and formed an atmosphere of rock vapor, which was also washed away by the solar wind.

A year of Mercury is equal to 88 days and a day is 59 Earth days. This planet rotates slowly around its axis but has the highest speed in the orbit of the Sun.

The surface of Mercury is similar to the surface of Earth’s moon, it is full of impact craters due to asteroid bombardment early in the formation of the solar system. Mercury’s craters and surface features are named after famous artists, musicians, and writers, such as Dr. Seuss, famous children’s author, and dancer Alvin Alley.

Very large impact basins such as Caloris with a diameter of 1550 km and Rakhmaninov with a diameter of 306 km were created by asteroid collisions in the early formation of the solar system. Although there are many flat lands on Mercury, some craters are hundreds of kilometers high. These rocks were formed when the interior of Mercury cooled and compressed over several billion years.

Although Mercury is the closest planet to the Sun, its surface can get very cold due to the lack of an atmosphere to trap heat. The temperature of this planet exceeds 430 degrees Celsius during the day, but it can reach minus 180 degrees Celsius during the night. Thus, with a temperature difference of 600 degrees Celsius, Mercury has the largest temperature fluctuation in the entire solar system.

Due to a lack of atmosphere and proper protection, the planet Mercury was not spared from the impact of asteroids in the early life of the solar system. The surface of this planet, like the moon, is full of impact craters.

Mercury completes the orbit of the Sun once every 88 days, and in other words, it travels 47 kilometers per second. This planet is the fastest planet in the solar system, But Mercury is not only fast but has an elliptical orbit. The distance of this planet to the sun can be close to 47 million kilometers and the farthest distance from the sun is 70 million kilometers.

Mercury has a huge iron core with a diameter of 3,600 to 3,800 km, which makes up nearly 75% of the planet’s diameter. In fact, the outer layer of Mercury is only 500 to 600 km thick. Much of Mercury’s core is made of iron, and scientists aren’t sure how it formed.

NASA’s MESSENGER probe orbited Mercury for more than four years and captured amazing images of it. Scientists used these images to create the first complete map of Mercury’s surface.

Mercury has the thinnest atmosphere among the planets of the solar system. Mercury’s atmosphere is so thin that scientists have named it the exosphere. Mercury’s exosphere is mostly composed of oxygen, sodium, hydrogen, helium, and potassium.

Scientists were surprised by Mercury’s strange magnetic field. The planet is too small to host a global magnetic field. Although its magnetic field is only one percent of the strength of Earth’s magnetic field, magnetic tornadoes are common there.

Mercury’s magnetic field interacts with the solar wind, and this process results in the generation of very fast magnetic tornadoes from the solar wind plasma. When the plasma of the solar wind hits the surface of Mercury, the neutral charge atoms are moved on the surface and transferred to the atmosphere of Mercury.

The transit of Mercury in front of the Sun occurs when this planet passes directly between the Sun and the planet in front of it and the solar disk appears opposite. During the transit, Mercury is seen as a small black dot that passes in front of the large orange disk of the Sun.

The transit of Mercury in comparison with the Earth happens more often than its transit in comparison with the planet Venus and it is repeated 13 or 14 times in every century. Mercury’s transit in front of the Sun usually occurs in May or November. Previous transits have occurred on these dates: November 15, 1999, May 7, 2003, November 8, 2006, May 9, 2016, November 11, 2019, and the next transit will be November 13, 2032. A typical transition lasts only a few hours. On June 3, 2014, the Curiosity rover observed the transit of Mercury in front of the Sun, marking the first time that a planetary transit has been observed from a planet other than Earth.

The oldest recorded records related to the observation of Mercury can be seen in the MUL.APIN tablets. These observations were probably made by Assyrian astronomers around the 14th century BC. Babylonian records of observing Mercury go back to the first millennium BC.

The first telescopic observations of Mercury were made by Thomas Heriot and Galileo in 1610. In 1612, Simon Marius noticed the change in brightness of Mercury according to its orbital position. In 1631, Pierre Gassendi made the first telescopic observations of the passage of this planet in front of the Sun, which had been predicted by Johannes Kepler.

Journey to Mercury

Accessing Mercury from Earth had many problems. One of the reasons for this problem was the excessive proximity of this planet to the sun. Spacecraft must have a high initial velocity to enter a Hohmann transfer orbit (an elliptical orbit used to transfer between two circular orbits in the same plane) near Mercury. The rocket fuel needed to travel to Mercury is more than the fuel needed to completely escape from the solar system; As a result, only two probes have managed to visit Mercury so far.

Mariner 10 was the first spacecraft to visit Mercury. This spacecraft sent clear images of Mercury to Earth and managed to study the environment and surface of this planet. Mariner 10 was the first spacecraft to visit two planets simultaneously in a single mission. Despite various mechanical problems during this mission, NASA gained a lot of information from this spacecraft; Therefore, Mariner 10 can be considered as the first NASA skill maneuver in which it has become professional today.

Before Mariner 10 launched from Cape Canaveral on November 3, 1973, little was known about the neighbors of our solar system. Mariner 10 visited Venus and Mercury with remarkable speed. Astronomers of that time were curious about the high density of Mercury and the material of its core. According to the hypotheses that NASA had previously proposed, the reason for this high density was the significant concentration of metal in the core of this planet; But questions were also raised about the exact type of core and how Mercury was formed.

Mariner 10 reached Mercury on March 29, 1974. The first images received from Mariner 10 showed a deserted planet with a surface similar to the surface of the Moon, Earth’s moon. Its holes and dry ground were clear in the pictures, But one of the major differences between Mercury and the Moon is the presence of rocks and deep valleys. According to scientists, the crust of Mercury has been wrinkled over time.

Messenger was the first Mercury orbiter. MESSENGER, short for Mercury Surface Space Environment Geochemistry and Ranging (Mercury Surface, Surrounding Environment, Geological Chemistry, and Ranging) mission, with a weight of 453 kg, investigated the nearest neighbor of the Sun and sent information and images of how the craters formed and its mysterious landscapes. Messenger’s mission ended on April 30, 2015, after the spacecraft ran out of fuel and hit the planet’s surface.

Messenger went hunting for water ice in the poles of Mercury and managed to discover it in the polar parts of this planet. In 2014, using MESSENGER data, researchers uncovered evidence of explosions that occurred on Mercury at different times. Meanwhile, data on water ice in the Brocofio crater near Mercury’s north pole was released in 2014. In the same year, Messenger temporarily went to a height of 100 km above the planet and had a better view of Mercury from this distance.

BepiColombo, a joint mission of the European Space Agency ( ESA ) and the Japan Aerospace Exploration Agency ( JAXA ), is the third exploratory mission to Mercury in the history of the space age. The two orbiters of this probe, the European Mercury Orbiter ( MPO ) and the Japanese Mercury Magnetospheric Orbiter ( MMO ), carry 16 scientific instruments that can answer these questions: Do impact craters in the poles of Mercury really have water ice? Where does Mercury’s magnetic field come from? What are the characteristics of the strange holes on the surface of Mercury?

The BepiColombo probe also captured its first images of Mercury during a low-altitude flyby on October 1, 2021. A total of 9 low-altitude flight maneuvers are planned until 2025.

The planet Mercury is the smallest planet in the solar system and the closest planet to the Sun, which revolves around it at the highest speed. Mercury does not have any moons and due to its close distance to the Sun, it has a thin atmosphere called the exosphere. The orbit of Mercury is elliptical and one year lasts 88 days and one day lasts 59 Earth days. The reason for the long days of Mercury is the slow rotation of this planet around itself. So far, three probes, Mariner, MESSENGER, and BepiColombo, have visited Mercury, but there are still many mysteries about this planet