The Closest Planet to the Sun
Our solar system is made up of 8 planets. Starting with the closest planet to the sun, the order of the planets is Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. This means Mercury is the closest planet to the Sun and the minor planet in the solar system. Read about this tiny planet’s size, orbit, and atmosphere.
Mercury’s Place in the Solar System
Mercury is not only the closest planet to the Sun, but it is also the minor planet in the solar system. Mercury is only just more significant than our Moon. Due to its proximity, the Sun appears three times larger and seven times brighter on Mercury than on Earth. The positioning of Mercury also means that it has very extreme surface temperatures. During the day, the surface temperature of Mercury can reach as high as 430 °C. In contrast, because Mercury has no atmosphere to keep heat, surface temperatures can get as low as -180 °C at night.
Mercury also has another title; it is the fastest planet in our solar system, traveling around the Sun every 88 Earth days. Its speed is actually how Mercury got its name, as the planet is named after the fastest of the ancient Roman gods.
The Smallest Planet in the Solar System
Along with all the other titles, Mercury is the most minor planet in our solar system, with a diameter of just 3,032 miles (ca. 4,880 km). To put this into perspective, Mercury is 20 times less massive than Earth and 2.5 times smaller.
The structure of Mercury is highly dense; in fact, it is second only to Earth in density. Mercury’s substantial metallic core takes up around 85% of the planet’s entire radius. Studies have shown that part of Mercury’s core is liquid. A further likeness between Mercury and Earth is that they both have a similar outer shell. Mercury has a fragile outer shell, even thinner than Earth’s, measuring just 250 miles (ca. 402 km) thick.
Mercury’s Orbit and Rotation
When we think of a planet’s orbit, we often think of a perfectly circular loop; however, this is not the case. Mercury’s orbit, for example, is more oval-shaped. During its orbit, Mercury’s closest to the Sun is 29 million miles away, and the furthest it gets from it is 43 million miles away.
As the fastest planet in our solar system, Mercury travels around the Sun every 88 days at an average speed of around 29 miles (ca. 47 km) per second.
Mercury spins pretty slowly on its axis, with one full rotation taking 59 Earth days to complete. As a result, when Mercury moves fastest in its elliptical orbit, its rotations are not accompanied by sunrise or sunset like on most other planets. Instead, the Sun appears to rise momentarily in the morning, after which it sets and, from some areas of the planet’s surface, seems to rise again. For the sunset, the reverse happens.
One solar day on Mercury, one complete day-to-night cycle is the equivalent of 176 days on Earth.
How did Mercury form?
Mercury formed around 4.5 billion years ago, resulting from gravity pulling swirling gas and dust together. Like all the other terrestrial (rocky) planets in our solar system, Mercury has a solid crust, a rocky mantle (a layer inside the planet locked between the planet’s core and the crust), and a central core.
During the early years of Mercury’s existence, it experienced several impacts from asteroids, which created colossal impact basins. These basins include Caloris, which is 960 miles (ca. 1,545 km) in diameter, and Rachmaninoff, which is 190 miles (ca. 306 km).
In addition to its craters and basins, Mercury has smooth terrain areas. However, Mercury also has several towering cliffs measuring hundreds of miles high. These cliffs formed as Mercury’s interior cooled down and contracted over the billions of years since its formation.
Another unique aspect of Mercury is that it spins at an almost entirely upright position. The consequence of this is that Mercury does not experience seasons as many of the other planets do.
What is Mercury like now?
The Atmosphere on Mercury
There is no atmosphere on Mercury, as we have on Earth, mainly due to the planet’s size and heat. Instead of an atmosphere, Mercury has a thin “exosphere” composed of atoms propelled off the surface by the solar wind and striking meteoroids. Oxygen, sodium, hydrogen, helium, and potassium make up most of Mercury’s exosphere.
The Magnetosphere on Mercury
The magnetic field is the area around a planet where the magnetic force is exerted. Magnetic fields around planets are created by churning motions of liquids at a planet’s core, which then conduct electricity and have an electric charge.
The magnetic field around Mercury is not very strong. It has just 1% of the strength of the Earth’s magnetic field. Mercury’s magnetic field does, however, interact a lot with the solar wind’s magnetic field from the Sun; this results in the formation of magnetic tornadoes!
Surface of Mercury
Mercury’s surface is covered in large craters created by collisions with meteors and comets. These craters and other features on Mercury are named after famous artists, musicians, and authors who have passed away. Among these famous names are Dr. Seuss, John Lennon, and the author of Breakfast at Tiffany’s, Truman Capote.
In terms of color, the surface of Mercury has a grey/brown color, with bright streaks known as ‘crater rays.’ These streaks are created when an asteroid collides with the planet’s surface. When this collision happens, a tremendous amount of energy is released, which bores a hole in the planet’s surface, and can crush large amounts of rock on impact. Some of this crushed debris is thrown far from the crater, eventually falling to the surface and creating the ‘crater rays.’ The finer particles of waste are much more reflective than the larger ones, which gives the rays a bright, eye-catching look.
Despite its boiling temperatures, Mercury has some water ice at its north and south poles inside deep craters. However, this only occurs in areas that are permanently under shadows. It gets cold enough to maintain water ice in these areas, even when other areas are scorching.
Proximity to the Sun: Mercury is the closest planet to the Sun.
Size of the planet: Mercury is the smallest planet in the solar system.
Length of a year: 88 Earth days.
Moons: Mercury does not have any moons.
Rings: Mercury does not have any rings.
The tilt of the axis: Mercury’s axis is only tilted 2 degrees.