The Planets: Mercury

Table of contents

Updated March 30, 2023 | Infoplease Staff

Mercury, the smallest planet in our solar system and the closest planet to the Sun, has long been a source of fascination for astronomers and space enthusiasts alike. Despite its small size and challenging environment, this enigmatic planet has much to teach us about the formation and evolution of our solar system.

The fastest planet, it is named after the Roman god Mercury who was the messenger of the entire Pantheon of deities, and known for his speed and mischievousness. These characteristics were also shared by the Greek equivalent and Olympian god, Hermes.

In this profile, we will explore the key characteristics and features of Mercury, as well as the ongoing efforts to explore and understand this intriguing planet. From the first flyby by NASA's Mariner 10 spacecraft to the latest data from the MESSENGER mission and upcoming flight plans, we will delve into the secrets of the innermost planet and what it can tell us about our place in the universe.

Characteristics of Mercury

Thanks to space exploration, technology, and strides forward in extraterrestrial imaging, including the Hubble Telescope and James Webb Space Telescope, the planet Mercury is able to be visualized and measured. Scientists and space enthusiasts alike can find an image of Mercury [] with reliable data, giving us a great peek at the smallest planet that is closest to the Sun!

Size and Density

Mercury is a small and rocky planet, with a diameter of just 3,031 miles. It is the smallest planet in our solar system, and the second densest after Earth. This high density is due to its large metallic core, which makes up about 75% of the planet's volume. Unlike Earth, Mercury has no atmosphere to speak of, which means that its surface is exposed to a harsh space environment.

The Surface

The planet's surface is heavily cratered, due to its lack of a robust atmosphere, with vast plains, cliffs, and valleys providing a rich array of geological features to study. Instead of having an atmosphere similar to that of earth-based locations, the Mercurial atmosphere is an exosphere, made up of oxygen, hydrogen, helium, sodium, and potassium. That means the surface of Mercury is not as protected from things like space object impact or space weathering, including solar wind and radiation. As such, like Earth’s moon, Mercury has experienced similar damage that has led to its pockmarked exterior.

One of the most striking features of Mercury is its vast network of impact craters, which have been left behind by meteoroids, asteroids, and possible comets bombarding the surface of Mercury for billions of years. Some of these craters are over 1,000 miles in diameter, and one of the most famous is the Caloris Basin, which is over 900 miles wide and was created by an impact that was so powerful, it caused shockwaves to ripple across the planet's surface.

Studying these craters and their characteristics can provide important information about the history of our solar system and the processes that shaped it. For example, the age and density of the craters across the planet’s surface can tell us about the frequency and intensity of meteoroid impacts in the early solar system.

Temperature

Despite being so close to the Sun, Mercury is not the hottest planet in our solar system, but does receive the most solar radiation of the other planets. Instead, Venus holds the title of “hottest planet”, with a thick atmosphere that traps heat and keeps temperatures at a steady 864 degrees Fahrenheit.

However, because of its proximity to the Sun, Mercury experiences extreme temperature fluctuations in surface temperature between its day and night sides, with temperatures reaching up to 800 degrees Fahrenheit on the day side and dropping to -290 degrees Fahrenheit on the night side.

Orbit

The small planet Mercury’s orbit is the shortest of any planet in our solar system, taking just 88 Earth days to complete one revolution around the Sun. The transit of Mercury is an elliptical orbit, meaning that the planet experiences a solar day (the time it takes for the planet to rotate once on its axis) that is twice as long as its year. Because of this, the planet's surface experiences some unusual effects, such as "tornadoes" caused by the interaction between its surface and atmosphere.

Magnetic Field

Mercury is also unique in that it has a very weak magnetic field, which is only about 1% as strong as Earth's. This magnetic field is thought to be generated by the planet's core, which is unusually large compared to its size.

Moons

Mercury is one of only two planets in the Solar System that do not have moons, with Venus being the other satellite-less planet. Indeed, though one of four the terrestrial planets, Mercury is actually smaller than other planets’ moons, such as Jupiter’s satellite Ganymede.

Exploration of Mercury

Scientists have been studying Mercury for decades, but it wasn't until the 1970s that we began to get a closer look at this intriguing planet. In 1974, NASA's Mariner 10 spacecraft became the first spacecraft to visit Mercury. It made three flybys of the planet, providing the first detailed images and data of its surface. Mariner 10 discovered that Mercury has a surprisingly large iron core, which was unexpected given its small size.

In 2008, NASA's MESSENGER spacecraft (which stood for MErcury Surface, Space ENvironment, GEochemistry, and Ranging) began orbiting Mercury and studying its geology, magnetic field, and composition in more detail. [2] The mission lasted for four years and provided a wealth of new information about the planet. MESSENGER discovered that Mercury's crust itself is rich in sulfur and potassium, and that the planet has a surprisingly weak magnetic field, which is only about 1% the strength of Earth’s. This magnetic field is thought to be generated by the planet's core, which is unusually large compared to its size.

Future Exploration of Mercury

While we have learned a great deal about Mercury in recent decades, there is still much more to discover. Scientists are already planning new missions to explore this fascinating planet in more detail.

One of the most exciting upcoming missions is the European Space Agency (ESA) and its ongoing BepiColombo mission, which will perform a Mercury flyby on June 20, 2023 [3]. This mission will consist of two orbiters, one from the European Space Agency and one from the Japanese Aerospace Exploration Agency. The orbiters will work together to study Mercury's surface, interior, and magnetic field, providing new insights into this enigmatic planet. A mission statement declares that arrival on the planet Mercury is projected for December 5, 2025.

The BepiColombo mission will build on the work of MESSENGER and Mariner 10, providing a more comprehensive understanding of Mercury's surface, space environment, geochemistry, and magnetic field. It will also study the planet's tectonic activity and volcanic history, as well as investigate its potential for hosting water ice in shadowed craters near its poles.

Messenger: Discovering the Secrets of Mercury

Mercury is a unique and intriguing planet that offers a wealth of opportunities for scientific exploration and discovery. Its small size, rocky surface, and extreme temperatures make it a challenging target for space probes, but also a valuable source of knowledge about the formation and evolution of our solar system.

For example, scientists could study the planet's tectonic activity and volcanic history, or investigate its potential for hosting water ice in shadowed craters near its poles. With ongoing research and exploration, we are sure to learn even more about this fascinating planet in the years to come.

If you want to continue exploring the galaxy, why not take our quiz on Mercury and see how well you do?