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.
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Mercury’s Poles Contain Water Ice Despite Its Proximity to the Sun
While we’re talking about ice, did you know that there are billions of tonnes of water ice residing at Mercury’s poles?
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9
Its Surface Temperatures Are Both Scorching Hot and Extremely Cold
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).
8
Mercury Doesn’t Have an Atmosphere, But a Paper-Thin Exosphere
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.
7
The Planet’s Surface Is Dotted With Massive Impact Craters
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.
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NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
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5
Mercury’s Metallic Core Is Unusually Large
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.
4
It’s Got an Unusually Strong Magnetic Field
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.
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NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
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!
1
We’ve Sent Only Three Missions to Mercury
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.
