We explain what Mercury is, its location in the solar system and its dimensions. Also, what are its characteristics, its climate and geological composition.
What is Mercury?
Mercury is the planet in the solar system closest to the Sun and the smallest. It is one of the inner or terrestrial planets, along with Venus, Earth and Mars.
With just 4,879 kilometers in diameter, it is a little larger than the Moon. It became the smallest planet in the solar system in 2006, after Pluto was no longer considered such and was classified as a dwarf planet.
Mercury is a rocky planet about which little was known until the visit of the Mariner 10 probe, which flew over it three times between 1974 and 1975 and obtained telescopic and radiometric images. Today it is known that its surface is covered with craters, similar to those of the Moon, due to the lack of a dense atmosphere to protect it from meteorite impacts. Additionally, it has regions at its poles that never receive sunlight, so they are covered by ice.
Due to its proximity to the Sun, Mercury's temperatures are very variable: the regions that are in shadow have a very low temperature, approximately -180 °C, while the areas illuminated by the Sun reach temperatures of more than 430 °C .
Additionally, like Venus, it is one of the two planets in the solar system that does not have natural satellites.
This planet receives its name from the god of Greco-Roman tradition Mercury (Hermes, for the Greeks), messenger of the gods and in charge of carrying the souls of the deceased to the entrance to the underworld. The choice of this name reflects the apparent speed of its movement in the sky.
- See also: Milky Way
Characteristics of Mercury
The main characteristics of Mercury are:
- It is the smallest planet in the solar system.
- It is the planet that is closest to the Sun.
- Its rotation is very slow compared to its translation.
- It has very variable temperatures, from -180 °C to 430 °C.
- Its surface is covered with craters produced by meteorite impacts.
- It has a large inner core composed mainly of iron and nickel.
Location and dimensions of Mercury
Mercury is the closest planet to the Sun, at a distance of 58 million kilometers. It has a highly eccentric orbit, meaning that its distance from the Sun varies considerably throughout its elliptical orbit. Its closest location reaches 46 million kilometers, but when it moves further away this distance extends to 70 million.
It has a diameter of 4,879 kilometers, making it the smallest planet in the solar system. Its rotation, that is, a complete turn around its own axis, takes 59 days and its translation time around the Sun is 88 days.
Seen from Earth, Mercury presents phases like the Moon. When it is between the Earth and the Sun, it is in its new phase: only its dark side can be seen from Earth and the planet appears in the sky near the Sun.
The transit of Mercury
The alignment between Mercury, the Sun and the Earth is called a transit. During a transit, a type of small, temporary eclipse occurs. From Earth's perspective, Mercury can be observed as a small black dot moving slowly across the Sun. This phenomenon occurs because the orbits of Mercury and Earth intersect at two points called nodes.
The phenomenon of Mercury transits has been observed for centuries. The astronomer Johannes Kepler first predicted a transit of Mercury in the 17th century, but the first one that was actually observed and recorded was on November 7, 1631 by the French astronomer Pierre Gassendi.
Transits of Mercury are events of great interest to astronomers because they provide valuable information. While this phenomenon lasts, they can measure the time it takes for Mercury to cross the solar disk, which helps them calculate relative distances and sizes in the solar system.
Mercury's atmosphere
Mercury's atmosphere is very thin and consists mainly of oxygen, sodium, hydrogen and helium. That is why the atmospheric pressure on the surface is minimal compared to that of the Earth. Furthermore, the scarce atmosphere and the lack of greenhouse gases that retain heat explain the temperature differences between shadow areas and those illuminated by the Sun, and between day and night.
Likewise, the lack of a significant atmosphere also means that Mercury lacks the climate dynamics found on planets with denser atmospheres like Earth. For this reason, it does not present rains, winds or notable atmospheric phenomena.
Composition of Mercury
Mercury's surface is rocky, similar to that of the Moon, with abundant meteorite craterswhich shows periods of great meteoric action and a very tenuous atmosphere that does not protect against impacts.
It also presents extensive plains and deep depressions, such as the Caloris and Rachmaninoff craters, 1,500 and 306 kilometers in diameter, respectively. In addition, it has other extensive plains that are less cratered and that may be due to volcanism processes that would have covered the surface with lava flows.
The internal structure of Mercury is believed to consist of the following components:
- Core. Mercury has a large metallic core compared to its size, which is a peculiarity. This core makes up about 85% of the planet's interior and is composed primarily of iron and nickel.
- Mantle. Mercury's mantle is the intermediate layer between the core and the crust, and is composed mainly of silicates.
- Crust. Mercury's crust is the thinnest layer on the planet. It is less dense than the mantle and core, and is composed mostly of silicate-rich rocks.
Explorations to Mercury
It is not easy to approach Mercury, given its proximity to the Sun and its lack of a braking atmosphere, so it has not been possible to study it in detail on many occasions.
The missions that have explored Mercury are:
- Mariner 10 (1974-1975). Launched in 1973, the Mariner 10 probe made three flybys of Mercury in 1974 and 1975. It provided the first close-up images of its surface and data on its atmosphere and topography. He discovered the existence of a magnetic field on the planet and mapped approximately 45% of its surface.
- MESSENGER (2004-2015). Launched in 2004, the MESSENGER (Mercury Surface, Space Environment, Geochemistry, and Ranging) probe orbited Mercury from 2011 to 2015. It provided detailed data on the geology, surface composition, atmosphere, magnetic field, and structure inner Mercury. It confirmed the presence of frozen water and organic compounds at the planet's poles, despite the high temperatures on its surface.
- BepiColombo (2018). The BepiColombo mission was launched jointly by the European Space Agency and the Japan Aerospace Exploration Agency in 2018. It is expected to reach Mercury in 2025.
- Venus
- Uranus
- Land
- Sun
- Moon
- Mars
References
- European Space Agency. (sf). All about Mercury. https://www.esa.int/
- Primary World. (sf) Mercury. https://www.mundoprimaria.com/
- Rodríguez, H. (2023). Mercury, the closest planet to the Sun. National Geographic. https://www.nationalgeographic.com.es/
