Mercury is the closest planet to the Sun and the smallest in the solar system. Compared to Earth, it is less than half its size and only slightly larger than the Moon. On its surface, the Sun appears three times larger than it does from Earth, and its light is seven times brighter. Despite its proximity to the Sun, Mercury is not the hottest planet in the solar system due to its lack of an atmosphere to retain heat. Temperatures on Mercury vary greatly, ranging from 430°C during the day to -180°C at night. Mercury orbits the Sun faster than any other planet, completing one orbit every 88 Earth days. It may appear as a bright star-like object but is difficult to observe due to its proximity to the Sun. It can only be seen under specific conditions, such as just after sunset or before sunrise, when it is close to the horizon.

Mercury is named after the Roman god of commerce and messenger of the gods, a reference to its rapid movement compared to other celestial bodies. Although challenging to observe, there is evidence that Mercury was recognized as early as the Sumerian era, around 5,000 years ago. Even in modern times, it has remained elusive; many astronomers spent their entire lives without observing it. The renowned astronomer Nicolaus Copernicus expressed regret on his deathbed for never having seen Mercury himself. In addition to its difficulty in observation, Mercury is distinguished by its smallest tilt and greatest orbital eccentricity among the planets. It has no moons and features a surface riddled with craters, indicating it has been geologically inactive for billions of years due to the near absence of an atmosphere.

Size and Distance of Mercury

Mercury has a radius of about 2,440 kilometers, just over one-third the width of Earth, making it roughly the size of a blueberry compared to Earth’s size. It is located at an average distance of 58 million kilometers from the Sun, or about 0.4 astronomical units (AU) away. Light from the Sun takes approximately 3.2 minutes to travel from the Sun to Mercury’s surface.

Orbit and Rotation

Mercury has a highly elliptical orbit around the Sun, with its closest distance to the Sun being 47 million kilometers and its farthest distance being 70 million kilometers. It completes one orbit around the Sun every 88 Earth days, traveling at a speed of 47 kilometers per second, making it the fastest planet in the solar system. However, it rotates very slowly on its axis, taking 59 Earth days to complete one rotation. As a result, a single solar day on Mercury (from sunrise to sunrise) lasts 176 Earth days. Due to its slow rotation and elliptical orbit, the Sun does not rise and set in a traditional manner. Instead, the Sun appears to rise briefly and then set before rising again in some areas of Mercury’s surface. Similarly, in other parts, the Sun appears to set and then rise again.

Formation of Mercury

Mercury formed about 4.5 billion years ago when gravity pulled together gas and dust to create this small planet closest to the Sun. Like other rocky planets, Mercury has a central core, a rocky mantle, and a solid crust.

Structure of Mercury

Mercury is the second densest planet after Earth, with a large metallic core that has a radius of 2,074 kilometers, approximately 85% of the planet’s total radius. Evidence suggests that much of this core is composed of liquid or partially molten materials. Its outer crust is similar to Earth’s outer shell (the mantle and crust) and is only about 400 kilometers thick.

The surface of Mercury resembles that of Earth’s Moon, marked by numerous impact craters from collisions with meteoroids and comets. These craters are named after famous artists, musicians, and authors, such as the children’s author Dr. Seuss and dancer Alvin Ailey. These craters likely formed early in the history of the solar system. The surface also features vast plains and long cliffs, some stretching hundreds of kilometers and rising over a kilometer and a half high.

Mercury’s surface appears brown and gray to the human eye, with bright lines called “ray craters” formed when an asteroid or comet impacts the surface, creating a massive explosion and ejecting large amounts of rock. These ejected fragments create bright rays on the surface. Over time, the space environment, affected by dust and solar wind particles, darkens these rays.

Temperature on Mercury

Mercury experiences extreme temperatures, reaching up to 430°C during the day. Due to its lack of an atmosphere to retain heat, temperatures can drop to -180°C at night. The planet may contain water ice at its polar regions within deep craters, but only in areas with permanent shadow where the temperatures are low enough to preserve the ice.

Instead of an atmosphere, Mercury has a thin exosphere composed of atoms blasted from its surface by solar winds and meteoroids. This exosphere mainly contains oxygen, sodium, hydrogen, helium, and potassium.

Magnetic Field

Although Mercury’s magnetic field is only 1% as strong as Earth’s, it interacts with the solar wind’s magnetic field to create intense magnetic storms. Occasionally, the hot, fast plasma from the solar wind strikes Mercury’s surface, causing ionized atoms to be ejected into the sky.

Possibility of Life on Mercury

Mercury’s environment is not conducive to life as we know it due to its proximity to the Sun, which results in extremely high surface temperatures and harmful solar radiation. Its thin atmosphere is incapable of protecting the surface, making it nearly impossible for living organisms to survive or adapt.

Space Missions to Mercury

Due to Mercury’s proximity to the Sun, direct observation from Earth is challenging, except during dawn or twilight when the Sun’s brightness does not overwhelm the faint light from Mercury. However, Mercury can be observed about 13 times per century during a rare event known as a “transit.” The first spacecraft to visit Mercury was NASA’s Mariner 10, which captured images of approximately 45% of its surface. The Messenger spacecraft flew by Mercury three times and orbited the planet for four years before crashing into its surface at the end of its mission.

Recently, the European Space Agency and Japan launched a joint mission to Mercury in 2018, consisting of two spacecraft that captured the first images of the planet during a flyby on October 1, 2021.