Mercury is the closest planet to the Sun in our solar system and the smallest of the eight major planets.
It has a diameter of about 4,880 kilometers, making it only slightly larger than our Moon. Due to its small mass, its surface gravity is only 38% of Earth's gravity. This means that an object that weighs 100 kg on Earth would weigh only 38 kg on Mercury.
Below we show a table of the main characteristics:
|
Position in the Solar System |
First planet from the Sun |
|
Diameter |
Approximately 4,880 km |
|
Time |
3.30 × 10^23 kg |
|
Gravity |
3.7 m/s² (38% of Earth's gravity) |
|
Rotation (sidereal day) |
59 Earth days |
|
Translation (orbit around the Sun) |
88 Earth days |
|
Solar day length |
176 Earth days |
|
Daily temperature |
Up to 430°C |
|
Night temperature |
Up to -180°C |
|
Atmosphere |
Virtually non-existent, composed mainly of oxygen, sodium, hydrogen, helium and potassium |
|
Surface |
Full of craters, similar to the Moon |
|
Core |
Large metallic core, composed of iron and nickel, occupies approximately 85% of the planet's radius |
|
Magnetic field |
Present, approximately 1% of the Earth's magnetic field |
|
Space exploration |
Visited by the Mariner 10 (1974-1975) and MESSENGER (2011-2015) missions |
|
Scientific importance |
Helps understand the effects of solar radiation and the early formation of the solar system |
Rotation and translation
One of the most interesting features of Mercury is its slow rotation combined with its rapid orbit around the Sun.
It takes Mercury 59 Earth days to complete one rotation on its axis, but it only takes 88 Earth days to complete one orbit around the Sun. This means that one day on Mercury (one complete day-night cycle) lasts 176 Earth days. As a result, one solar day on Mercury is actually two Mercury years long.
Linear and angular speed
Mercury has a highly elliptical orbit that takes it to an average distance of 57.91 million kilometers from the Sun. Its linear speed in this orbit is approximately 47,856 km/h, making it the fastest planet in our solar system. This high speed is because it must generate a large centripetal force to compensate for the strong gravitational pull of the Sun.
Mercury's angular velocity is approximately 8.26 × 10⁻⁷ radians per second. This measurement describes the angle that Mercury travels in its orbit per unit of time. Due to its short orbital period of only 88 Earth days, Mercury completes its orbit quickly compared to other planets.
Surface and atmosphere
Mercury's surface is covered in craters, similar to those found on the Moon that are the result of asteroid and comet impacts over billions of years.
As far as the atmosphere is concerned, Mercury does not have a significant atmosphere that could protect its surface from these impacts or cause erosion.
Temperature
Mercury is the planet with the highest temperature range in the Solar System: between 430 and -180 degrees Celsius.
Due to its proximity to the Sun, Mercury experiences extreme temperatures. During the day, temperatures can reach the aforementioned 430 degrees Celsius.
However, due to the lack of a heat-retaining atmosphere, nighttime temperatures can drop to -180 degrees Celsius.
Internal structure
Mercury is believed to have a large metallic core composed primarily of iron and nickel that occupies approximately 85% of its radius, which is disproportionately large compared to the other terrestrial planets.
Above the core, there is a thin mantle rock and a relatively thin crust as well. The large proportion of the core suggests that Mercury may have suffered a giant impact in the past that removed much of its original mantle and crust.
Magnetic field
Despite its small size and slow rotation, Mercury has a magnetic field, although it is much weaker than that of the Earth, approximately 1% of the Earth's magnetic field.
However, its existence is surprising and has been the subject of much study. Mercury's magnetic field is believed to be generated by the dynamics of the liquid metallic core.
Scientific explorations
To date, Mercury has been visited by two major space missions. The first was NASA's Mariner 10 mission, which made three flybys of Mercury between 1974 and 1975, providing the first detailed images of the planet's surface. The second was the MESSENGER (MErcury Surface, Space ENvironment, GEochemistry, and Ranging) mission, also from NASA, which entered orbit around Mercury in 2011 and continued studying the planet until 2015.
MESSENGER collected a wealth of data on the composition of Mercury's surface, its magnetic field and its exosphere (a tenuous shell of atoms and particles that surrounds the planet).
Scientific importance
The study of Mercury is important for several reasons. As the closest planet to the Sun, Mercury offers a unique opportunity to study the effects of intense solar radiation and the solar wind on a rocky planet. Additionally, Mercury's composition and structure may provide clues to the processes that occurred during the early formation of the solar system.
It is believed that knowledge of the characteristics of Mercury can also facilitate the study of exoplanets that orbit close to their stars since many exoplanets discovered so far have orbits very close to their stars, similar to Mercury's orbit around the Sun.
Why is it called Mercury?
The planet Mercury owes its name to Roman mythology. The Romans named it after their god Mercury, the messenger of the gods, known for his speed and agility. This choice was due to the speed with which the planet Mercury moves across the sky.
By observing it, ancient astronomers noted that Mercury is fast moving compared to other planets, completing one orbit around the Sun in just 88 Earth days. This swift movement evoked the image of Mercury, the winged god, who moved quickly to accomplish his tasks, carrying messages and performing missions for other gods.
The planet also has other nicknames:
Yes, Mercury has several nicknames due to its characteristics and history in astronomy. Some of the most common include:
- "The messenger of the gods" : for the reason stated above.
- "The morning star" and "the evening star" : This name is because Mercury can often be seen near the horizon shortly before sunrise or shortly after sunset.
- "The Flashing Planet" : Due to its proximity to the Sun, the planet is visible only for brief periods during twilight and is not visible during most of the year. This makes it appear "intermittent" in its visibility from Earth.