Mercury information for kids

This article is a quick reference sheet on information about the small planet of Mercury.

Photo Credit: NASA
By Robbi Erickson

The planet Mercury was named after the mythological winged messenger. It is the second smallest planet in our solar system, and it is so small that there are two moons in our solar system that are bigger than this planet, Ganymede that orbits Jupiter, and Titan that orbits Saturn. It has a diameter of 3,000 miles and a year length of 88 Earth Days. To get a better idea of how small Mercury is we can compare its diameter of 3,000 miles to Earth’s diameter of 6,378 miles. The Earth is more than two times as wide as Mercury. Or, for another comparison it is only a little more than twice as big as our moon that has a diameter of 1,738 miles. While this planet is much smaller than the Earth, it spins on its access much slower, and because of this, each Mercury day is equal to 176 Earth Days.

Mercury is also the closet planet to the sun, and because of its closeness to the sun it has very dramatic characteristics. Mercury has a stretched out orbit, or elliptical orbit around the sun. This means that its distance from the sun varies depending on its position in the ellipse. This distance ranges from 27 million miles away from the sun to 41 million miles away from the sun. The variation in its distance from the sun also affects the surface temperature of the planet. As Mercury orbits away from the sun its average surface temperature drops, and as it orbits closer to the sun its average surface temperature increases. Generally Mercury’s surface temperature fluctuates by 920 degrees Fahrenheit every day. When it faces towards the sun its surface temperature is 650 degrees Fahrenheit, and when it turns away from the sun and faces the darkness of space its surface temperature drops to 270 degrees below zero Fahrenheit.

Mercury, like the Earth, Venus, and Mars, is a rocky planet. When Mariner 10 visited this tiny planet it took pictures of Mercury’s surface showing that it had been bombarded with thousands of meteors. These meteor hits left the planet’s surface full of craters. Compared to Earth and the other planets in the solar system, Mercury is a very dense planet. This means that molecules that make up the planet are held together tightly. It is made up of mostly iron, but because it turns so slowly, and because it is so small, it only has a weak magnetic field that is not strong enough to attract a moon, so Mercury is moonless. One amazing, and astounding fact about Mercury is that even though it is located very close to the sun, and has can have high surface temperatures, scientists have observed ice on Mercury’s poles. Its atmosphere is made up of a lot of the same elements as Earth’s atmosphere, however Mercury has a different combination of concentrations of these elements. For comparison, the Earth’s main components of its atmosphere are 78.084% Nitrogen (N2), and 20.946% Oxygen (O2), while Mercury’s atmosphere is made up of 42% Oxygen (O2), 29% Sodium (Na), 22% Hydrogen (H2), 6% Helium (He), 0.5% Potassium (K), possible trace amounts of Argon (Ar), Carbon Dioxide (CO2), Water (H2O), Nitrogen (N2), Xenon (Xe), Krypton (Kr), Neon (Ne)

There really is not a lot known about Mercury. This is because it is a difficult planet to observe. Its closeness to the sun makes it too dangerous to send a manned mission to explore it, and it also makes it too dangerous to have the Hubble Telescope take pictures of it. Another fact that makes Mercury difficult to study is that it orbits so quickly around the sun it is hard for scientists to see it. In fact, it is only visible here on Earth a few times a year for a very short period of time, usually only lasting a day or two.