When it is closest to the sun, it is just 29 million miles (47 million km), yet when it is farthest away, it is 43 million miles (70 million km). So, its average distance from the sun is 37 million miles (59 million km).
This is about 8% of the distance between the Earth and the Sun. It takes Mercury 4 months 17 days to orbit the Sun, so it returns to the same part of the sky each time. Because of this, astronomers can see all the way back to where Mercury was in the night before it was last seen over the horizon.
At first glance, it might seem like a lot of space, but if you zoom out from Earth, most of what you see is empty space. The only objects that are important enough to note here are the planets, which fill up only about 1/300th of one percent of the sky.
Mercury has no atmosphere or water, so there are no clouds or weather to speak of. All we know about Mercury's interior is that it must be mostly rock, because there is no evidence of any kind of surface water or air. It probably formed with most of the other planets at almost the same time as the rest of the Solar System, more than four billion years ago.
Mercury, for example, is around 36,250,000 miles from the sun on average. If we divide 36,250,000 by 91,000, we get 398 inches – or around 33 feet – distant from the basketball in our model. This means that the sunlight reflecting off of the mercury would be reduced to about one-third of what it is now.
The earth is about 12,900 miles away from the sun. So if the mercury were at the center of the earth, the temperature would be 438 degrees Fahrenheit (225 degrees Celsius). That's too hot to live in.
The core of the earth is about 6,400 miles inside the planet. So the mercury would be deep within the core of the earth if it were at the center of the planet.
The core is mostly liquid iron with some protons and neutrons mixed in. It's so hot that any matter that falls into it is instantly vaporized—including the mercury.
Since no part of the mercury is ever exposed to the cold light of day, it must always remain molten. And because mercury is more dense than air, all the heat from the sun goes into melting it, not warming it up as much as other elements like silicon or oxygen.
Mercury, at a distance of 57 million kilometers from the Sun, is the nearest planet to the Sun (35 million miles). Mercury is the smallest of the terrestrial planets. It has a diameter about one-third that of Earth's. Its mass is about 58 percent that of Earth's.
Like the other planets, Mercury orbits around the Sun in an almost circular path, but this path is very close to the Sun's center. Thus, all points on Mercury are either always in darkness or always in light. Because there is no atmosphere to scatter sunlight like that of Venus, most of Mercury is visible to the naked eye. In fact, if you were to look directly at the Sun, you would see its entire surface, except for the shadow of the Earth, which covers half of it. But because Mercury is so small, you could only see part of it at a time.
Kids will love learning about how far away different planets are from the Sun. Learning about astronomy is a great way for kids to learn about physics and chemistry too! The closer a planet is to the Sun, the hotter it gets. The farther out it is, the cooler it gets.
In addition to being very small, Mercury has no natural resources that we know of. So it must get all of its energy from the Sun.