26-02-2025
10 Facts About Mercury That Prove It's More Than Just the Smallest Planet
Mercury, the smallest planet in our solar system, named after the Roman god of commerce, is the planet closest to the Sun. It also circles the Sun the fastest, at an average speed of almost 106 thousand miles. This is just the tip of the iceberg regarding cool facts about Mercury.
While we're talking about ice, did you know that there are billions of tonnes of water ice residing at Mercury's poles?
Despite being very close to the Sun, and Mercury's surface having scorching-hot temperatures when its surface is lit up by the Sun, areas located at Mercury's north and south poles are concealed in permanent shadows. This allows water to exist in the form of ice in these freezing cold, permanently shrouded regions.
The first piece of evidence for water ice on Mercury's moons was gathered by the MESSENGER (MErcury Surface, Space ENvironment, GEochemistry, and Ranging) spacecraft, which did several flybys over Mercury between 2008 and 2015.
Being the planet closest to our Sun, it's no surprise that the surface temperature on Mercury can reach 800 degrees Fahrenheit (427 degrees Celsius).
But what's interesting is that because it has no atmosphere at all, surface temperatures can drop to -290 degrees Fahrenheit (-179 degrees Celsius) during nighttime.
For reference, absolute zero, the lowest temperature possible, occurs at -460 degrees Fahrenheit (-273 degrees Celsius).
Yes, Mercury doesn't have an atmosphere. This is because the planet has too weak gravity to form an atmosphere and because, being so close to our star, Mercury is constantly smashed by ludicrous amounts of solar radiation.
The solar wind affects particles on the planet's surface, blasting them off it. These atoms, along with atoms and particles launched off the surface by meteor strikes, create a thin exosphere made of oxygen, sodium, hydrogen, helium, and potassium.
For billions of years, numerous meteors, asteroids, and comets have impacted Mercury, turning the planet's surface into a scarred landscape dotted with craters.
The largest crater has a diameter of about 950 miles (1,529 km) and is called the Caloris Basin. The second-largest crater on Mercury is called Rachmaninoff, which is about 190 miles (306 km) in diameter.
Both craters were created during the early days of our solar system by large asteroids that blemished the planet's surface for eons to come. A number of craters are named after renowned artists, with one crater named after Dr. Seuss.
Due to its crater-scarred surface, lack of atmosphere, and tiny size, the surface of Mercury is most similar to Earth's Moon. While similar to Mercury, our Moon hasn't showered with immeasurable amounts of solar radiation, and its core has cooled off eons ago.
Mercury's metallic core is most likely partly molten or fully liquid billions of years after the planet's formation. Since its core is still cooling off, Mercury is slowly shrinking.
The said metallic core is unusually large, making up about 85% of the planet's radius. For comparison, the Earth's core makes up only about 30% of our planet's radius.
The popular explanation for decades was that numerous impacts over billions of years stripped a good chunk of Mercury's rocky crust, ultimately leaving it with an unusually large metallic core.
However, a study found that Mercury can thank the Sun and its humongous magnetic field, which captured iron particles during the early days of our solar system and pulled them closer to it, for the planet's massive core. As the planets had started forming, planetary accretion disks closer to the Sun ended up accruing more iron particles than the outer planets' accretion disks.
Mercury's massive metallic core, which is likely still liquid, creates a magnetic field that's unusually strong for such a tiny body. While it only has about 1.1% of the strength of Earth's field, it's strong enough to slow the solar wind, instigating a magnetosphere.
Being so close to the Sun means that Mercury's magnetic field interacts with the solar wind from the Sun, creating monstrous magnetic tornadoes ravaging across the planet's surface.
While it's definitely a planet, Mercury is quite small. With a radius of only 1,516 miles (2,440 km), Mercury's width is a bit more than one-third of Earth's, which has a radius of 3,963 miles (6,378 km).
In fact, the planet's so small that two of our solar system's moons, Jupiter's Ganymede (the largest moon in the solar system) and Saturn's Titan, are both larger than Mercury.
While Mercury has a diameter of 3,032 miles (4,880 km), Ganymede has a diameter of 3,270 miles (5,262 km), and Titan is 3,199.73 miles (5,149.46 km) across.
One day on Mercury, the time needed for the planet to fully rotate around its axis, lasts about 58.6 Earth days. One year on Mercury, equal to one full orbit around the Sun, is 88 Earth days long.
On the other hand, one solar day on Mercury, defined as the interval between two meridian transits of the Sun (sunrise to sunrise), lasts 176 Earth days and is as long as two Mercury years!
Mercury wasn't of much interest to NASA and other space agencies. To date, the planet has been visited by only two missions: Mariner 10 and MESSENGER.
Mariner 10 visited Mercury in 1974, providing the first detailed images of the planet's surface. MESSENGER performed multiple flybys of Mercury, the first one taking place on January 14, 2008. Between 2008 and 2015, MESSENGER sent smorgasbords of data to Earth, and mapped the entire surface of Mercury.
Another mission, BepiColombo, a joint venture between The European Space Agency and the Japanese Space Agency, is on its way to Mercury. The two probes (Mercury Planetary Orbiter and Mercury Magnetospheric Orbiter) are set to study the planet's magnetosphere and map its surface. They should arrive at Mercury in November 2026 after performing six flybys of the planet.
Mercury is one of my favorite planets, but that doesn't mean the rest of them aren't endlessly interesting too; there are plenty of mind-blowing space facts that are hard to believe.
