Become an expert on Mercury in 5 minutes or less
1. It is the closest planet to the Sun.
It orbits at a distance of approx 36 million miles (58 million km) or 0.4 AU. One day on Mercury is equivalent to 59 Earth days, but one year is just 88 Earth days.
2. It is not the hottest.
You would expect the closest planet to the Sun to also be the hottest, but it’s not. This honor goes to Venus which has an extremely dense atmosphere that creates a greenhouse effect generating temperatures up to 870 F (465 C). By comparison, Mercury’s temperature only reaches about 800 F (427 C).
3. Temperatures can change very fast.
Despite not being the hottest planet, Mercury does experience some very bizarre temperatures. Because it has virtually no atmosphere, Mercury is very bad at retaining heat. Therefore, while temperatures can get very high during the day, they also get extremely cold at night – around -280 F or -173 C. This is the greatest variation in temperature seen on any planet surface.
4. It’s not very big.
Mercury has a diameter just over 3,000 miles (4,800 km). Despite being a planet, Mercury is pretty tiny and several moons like Titan (Saturn) and Callisto and Ganymede (Jupiter) are actually larger than it. Even our own Moon isn’t that much smaller than it.
5. It is incredibly dense.
In fact, the only planet which is denser than Mercury is Earth. This is because most of the planet is made out of rock and heavy metals. In fact, Mercury is the most iron-rich planet in the solar system. It also has a huge core relative to its size (over 40% of the planet). What is even more surprising is that it might still be molten instead of a solid piece of iron. When our spacecrafts went to study Mercury, they discovered faint traces of a magnetic field.
6. It has ice.
Despite being incredibly close to the Sun, mercury has ice-filled craters. This was first detected in 1991 using radar observations and confirmed through images last year. The ice is located at the poles of the planet which are constantly bathed in darkness so temperatures remain very low.
7. We haven’t studied it that much.
So far, only two spacecrafts have ever been to Mercury. The first was Mariner 10 in 1973 and the second one, MESSENGER, was launched 31 years later. We’ve also never looked at it through the Hubble Telescope. Mercury is too close to the Sun and the reflected light would damage the telescope’s optics.
8. It kinda looks like the Moon.
Besides the similar size, Mercury has other things in common with our Moon. The lack of an atmosphere makes the surface of the planet look just like our Moon and, as it turns out, it is also full of craters after billions of years of impacts. We didn’t find this out until the early 1970s when we took flyby pictures of Mercury. Until then, we thought that the surface of the planet would be completely smooth.
9. It has a weird orbit.
Like most planets, Mercury doesn’t orbit its star in a perfect circle, but rather an ellipse. However, the difference between aphelion and perihelion (longest and shortest distances) is pretty staggering. At its closest, Mercury is about 29 million miles (46 million km) from the Sun. At its furthest, it’s 44 million miles (70 million km).
10. You can see it, but it’s tricky.
Despite being one of the closest objects to us and one of the brightest things in the sky, it’s pretty hard to see Mercury. This is because it is very close to the Sun so it usually gets overshadowed. You can normally catch a quick glimpse of it in the right conditions about half an hour after sunset or half an hour before sunrise.
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