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What is Mercury?

September 25, 2012

Hi, I’m Emerald with RedOrbit. In this “What Is” video we get up close and personal with Planet Mercury.

Named after the Roman messenger of the gods, Mercury is the innermost and smallest planet of the solar system.  Only slightly larger than Earth’s moon, Mercury appears from Earth as a morning and evening star, but is difficult to see due to its closeness to the Sun.

On Mercury, the sun appears about 3 times larger in the sky than on Earth, and its rays are almost seven times as strong. Mercury’s proximity to the Sun is also a factor in why it has no moons. The sun’s gravity would strip it of any satellites.

Like the other inner planets, Mercury is dense, and rocky. In fact, it’s the second densest planet next to Earth.  NASA’s Messenger spacecraft revealed that Mercury has a large core, occupying nearly 85% of the plant’s radius. The planet’s small mass means its force of gravity is barely a third of the Earth’s.  A 100-pound person on Earth would weigh only 38 pounds on Mercury.

Mercury’s weak atmosphere is barely detectable, so most asteroids and meteorites smash into the planet rather than burn up in the atmosphere. For that reason, Mercury’s surface is pockmarked with craters, much like our Moon.  In fact, Mercury has the largest known impact crater in the solar system.

If planetary orbits were racetracks, Mercury would always be victorious. It orbits the sun in only 88 days…. faster than any of the 8 major planets. It also spins very slowly upon its axis, so a single day on Mercury takes almost 59 Earth days.  Mercury has a highly elliptical orbit. At its closest point it’s 29 million miles from the Sun, but at its farthest point it’s 43 million miles away. For this reason surface temperatures can vary from 800 degrees Fahrenheit to a frigid 300 degrees below zero.

Interestingly, even though Mercury is closest to the sun, it’s only the second hottest planet in our solar system. The award for the hottest planet goes to the second planet from the Sun… Venus.



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