Facts about Mercury (everything you need to know in 2019)

Mercury is the smallest planet in Earth’s Solar System and the closest to the sun. But what is it like there and how does it compare to the other planets?

Below are all the facts about Mercury that you could possibly want.

Where is Mercury in the Solar System?

Mercury is the closest planet to the Sun and is situated fairly close to Earth as well, with Venus in the middle. This closeness to the Sun means Mercury revolves around the Sun faster than any other planet. Once every seven years or more, Mercury can be viewed from Earth moving across Sun’s face. This occurs as the planet’s orbit is tilted by seven degrees to Earth’s orbital plane. This phenomenon is referred to as ‘transit’.

Mercury moves or revolves around the Sun at the speed of 180,000 kilometers per hour, which is the fastest of all planets. As a result, the planet completes an entire trip around the Sun in just 88 Earth days. However, its rotation speed is slow – much slower than Earth. This means a day on the planet lasts close to 59 Earth days. Mercury’s spin is slow and the years are short. It takes quite a while for Sun to show up and set. In fact, the planet witnesses a sunrise only once every 180 (Earth) days. This quick orbiting led to early civilizations believing the planet was two different stars – one appearing in the morning and the other showing up in the evening.

What’s it like on Mercury?

Due to its extreme proximity to the Sun, the surface temperature of Mercury can reach 450 degrees Celsius. But as the planet doesn’t have any real atmosphere, heat doesn’t get entrapped and night temperatures could go down significantly – as low as -173 degrees Celsius. This temperature difference is the biggest of all planets in our solar system. By the way, Mercury isn’t the hottest planet. That title goes to Venus.

Despite being so close to the Sun, water has been found within the planet’s craters in the north. These could be regions permanently shielded from the Sun’s heat. The southern pole has icy pockets, which may be the result of meteorites or comets delivering ice there. Or perhaps, water vapor could have moved from the interiors and become frozen at the poles.

The lack of an atmosphere means foreign objects can easily land on the planet. The planet has multiple craters, which have caused significant disfigurement. In fact, approximately four billion years ago, Mercury was struck by a 100-kilometer wide asteroid. The resulting impact was equivalent to a trillion megaton bombs, leaving behind a huge impact crater roughly 1,550 kilometers wide. The planet has the most impact and crater marks among all planets, and which also makes it look like Earth’s moon from a distance. Also, Mercury is not active geologically, which means it cannot heal itself from the impacts made by comets and asteroids.

Most Mercurian craters get named after famous artists and writers. Craters bigger than 250 kilometers in diameter are called ‘basin’. The largest basin is the Caloris Basin, which was found by Mariner 10. It is approximately 1,550 kilometers in diameter and can encompass Texas completely.

It’s believed a major impact could have also caused Mercury’s odd spin. A study carried out in 2016 stated Mercury had had its fair share of volcano eruptions some 3.5 billion years ago. The volcanic activity, which is now extinct, could have also constantly reshaped Mercury’s surface.

Instead of a real atmosphere, the planet has an extremely thin “exosphere” composed of atoms that exploded on the planet’s surface through solar radiation, micrometeoroid impacts, and solar wind. The exosphere comprises oxygen (42 percent), sodium (29 percent), hydrogen (22 percent), helium (6 percent), potassium (0.5 percent), and possible trace quantities of carbon dioxide, argon, nitrogen, water, neon, xenon, and krypton. Due to the lack of much gravity on Mercury, the planet isn’t capable of holding its atmosphere. The solar winds, in fact, blow away the atmosphere. But those solar winds are also instrumental in transporting in new gases, dust from micrometeorites and radioactive decay.

What is Mercury made up of?

Like Earth, Mars, and Venus, Mercury is also a rocky planet. The planet is composed of one continental plate atop a cooling core of iron. With cooling, the core solidifies, decreasing Mercury’s volume and forcing it to shrink. Mercury’s metallic core is 3,600 to 3,800 kilometers wide and it makes up almost 40 percent of the planet. Earth’s core volume is 17 percent, by the way.

The outer shell (mantle and crust) is just 500 to 600 kilometers thick, which is extremely thin. Comparatively, Earth’s mantle is 2,900 kilometers thick and the crust is 40 kilometers thick. Like Earth, Mercury is also a tectonically active planet.

A 2016 study indicated that the planet’s surface traits could primarily be classified as older interior material and newer surface material. The older material melted at increased pressures at the boundary of the core-mantle. Another study in the same year found the dark color of the planet’s surface is because of carbon, which is believed to be primordial crust remnants.

Scientists state Mercury’s core is most likely molten. The claim is debatable, but there are more pieces of evidence proving the molten core’s existence. Mercury’s rotation is wobbly at best. The sloshing happening within the liquid core could be causing these minor variations in rotation. A solid core would not let the wobble and ensure a rigid rotation. Moreover, radio waves also bounce off the planet, lending more credence to the “liquid core” claim.

Mercury’s Magnetic Field

Mariner 10, the first Mercury mission from Earth, discovered Mercury had a magnetic field. Theoretically, planets develop magnetic fields if they spin fast and have a molten core. However, Mercury’s magnetic field is different in comparison to Earth. And the unusual interior could be the reason for it. MESSENGER’s observations stated that Mercury’s magnetic field is three times stronger (approximately) at the northern hemisphere compared to its south.

During 2007, radar observations from Earth discovering Mercury’s core being molten may help clear the air about the planet’s magnetism. However, solar wind could be instrumental in dampening that magnetic field. Though the magnetic field of Mercury is only a percent of Earth’s strength, it’s active. The solar wind’s magnetic field touches upon the planet’s field periodically, generating the magnetic tornadoes that direct the wind’s hot plasma to Mercury’s surface.

How big is Mercury?

Mercury is the smallest of all planets. It is smaller than Earth and is only marginally bigger than Earth’s moon. To give you some perspective, 18 Mercury’s put together would make one Earth. Mercury is not just small but is suspected to be decreasing in size with time, thanks to the cooling iron core.

facts about mercury
This view of Mercury was produced by using images from MESSENGER. These colors are not what Mercury would look like to the human eye, but rather the colors enhance the chemical, mineralogical, and physical differences between the rocks that make up Mercury’s surface. Credit: NASA

Is there life on Mercury?

There is no life on Mercury. The planet has some extreme temperatures, which the Earth has probably never recorded in its history. It gets extremely cold and also extremely hot, which is why life is unlikely on the planet.

Does Mercury have moons?

Mercury doesn’t have any moons, and this can also be attributed to the planet’s lack of atmosphere and low gravity. And since the planet is so close to the Sun and the Sun’s gravity power is extremely strong, even if an object approached Mercury, it would invariably get pulled in by the gravity of the Sun. This probably also explains why Venus, the second closest planet to the Sun, doesn’t have a natural satellite or moon of its own.

This visible-infrared image shows an incoming view of Mercury, about 80 minutes before NASA’s MESSENGER spacecraft’s closest pass of the planet on January 14, 2008, from a distance of about 27,000 kilometers (17,000 miles). Credit: NASA

What missions have humans sent to explore Mercury?

Mercury is extremely close to the Sun, which makes it harder to study the planet. In fact, there have been no manned expeditions from Earth to Mercury till date for this very reason. However, a couple of robotic space expeditions have been initiated in the past.

Mariner 10 was the first spacecraft that headed to Mercury. NASA launched the robotic space probe on November 3, 1973, and it was the last of the Mariner program spacecraft. Mariner 9 was launched approximately a couple of years ago. The goal of Mariner 10 was to fly by both Mercury and Venus and measure both planets’ atmosphere, environment, body, and surface.

The spacecraft managed to fly by Mercury three times. It imaged close to 45 percent of the planet’s surface, besides detecting Mercury’s magnetic field. It came up with close-up images of the planet and also investigated into the planet’s surface and environment. Also, it delved into learning how Mercury and solar wind interacted with each other.

With maneuvering gas getting close to exhaustion, Mariner 10 began to orbit the sun one more time. Engineering tests happened till March 24, 1975, when the nitrogen supply’s final depletion was signaled. Commands from Earth were immediately sent to Mariner 10 to turn its transmitter off, and radio signals from the spacecraft to Earth stopped. The spacecraft is still believed to be orbiting the Sun. However, the Sun’s radiation would have most likely damaged its electronics. After the cut in transmission, the spacecraft hasn’t been tracked or spotted from Earth.

Post-Mariner 10, more than three decades went by without a spacecraft being sent to the planet. The MESSENGER orbiter by NASA was the next spacecraft to head to Mercury. It was launched on August 3, 2004. And in March 2011, it was the first spacecraft to have orbited Mercury. It orbited Mercury between 2011 and 2015. The robotic spacecraft was launched to study Mercury’s geology, chemical composition, and magnetic field. The spacecraft came up with information about water on the planet.

MESSENGER entered terminal orbital decay phase during late 2014. Its operation duration was increased by many weeks, capitalizing on the remaining helium gas supply it had. The gas was used for pressurizing the propellant tanks. During this decay phase, MESSENGER kept studying Mercury. On April 30, 2015, it crashed onto Mercury’s surface, invariably making a crater approximately 16 meters wide.

List of key facts about Mercury

  • Distance from Earth: 77,000,000 kilometers
  • Distance from Sun: 57,909,175 kilometers
  • Temperature: -173 degrees Celsius (minimum) and 450 degrees Celsius (maximum)
  • Mass: 3.30 × 10^23 kg (Earth’s 5.5 percent)
  • Surface area: 74,800,000 km²
  • Volume: 6.083 x 1010 cubic kilometers
  • Diameter: 4,879 kilometers
  • Radius: 2,440 kilometers
  • Orbital period: 88 days

Sources and Further Information

Read more about the other planets of the Solar System

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