Mercury, one of the five classical planets visible with the naked eye, is named after the fast-footed Roman messenger deity. Although it is unknown when the planet was discovered, astronomers Galileo Galilei and Thomas Harriot first viewed it using telescopes in the seventeenth century. They observed that it moved slowly across the sky and was therefore not a fixed star.
Galileo described it as "a small but very bright body" that moved slowly through the night sky. He also noted its relationship to the other planets, saying it followed along behind Jupiter but was still able to be seen when that planet was below the horizon.
Harriot collected data on the positions of several stars and planets over several nights and found that none of them stayed put relative to any other object. This means that they were all moving around something else--probably another planet--but what that something else was Harriot could not say. He may have suspected it was Earth because it was known that the Sun and Moon moved around the Earth, but he did not know this at the time of his observations.
More than 200 years later, scientists are still discovering new things about Mercury. In 2006, for example, NASA's Messenger spacecraft arrived at the planet and began taking pictures and making measurements. So far, the data have revealed that Mercury has a thin veneer of atmosphere, no global oceans, and an iron core.
What is the origin of the name Mercury? The Romans believed that gods and goddesses oversaw all aspects of life on Earth. Mercury is named after the gods' messenger. The Roman Mercury wore a helmet with wings and wore shoes with wings. He was also called Hermes because he could lead people from one place to another by flying with his magical staff.
Hermes led the souls of the dead to the afterlife. He did this by way of a special path for him to follow. This path was called the "road of the sun" and it went through twelve cities in Italy. At each city, there was a god who could either help or hinder Hermes on his journey. If he was being helped, then Hermes would give that city's citizens gifts before moving on to the next place. If he was being held up, then it meant that the next city on his route had been visited already. There were also islands near Italy where Hermes stopped to rest during his trip home for the summer. One of these islands is called MERCURY ISLAND.
The Romans believed that their gods took care of everyone, even strangers. They asked Mercury to watch over travelers so they wouldn't be injured or robbed while away from home. Because of this, the Romans named the planet after the God of Messengers and Thieves.
If you monitor it between July 20th and August 9th, you'll notice Mercury wandering, offering strong evidence that it is, in fact, a planet. Infrared images (center, 2007) can be rebuilt, or the Messenger mission can fly to Mercury and photograph it directly (right).
Why do we know this? Because the Astronomical Unit (AU), the average distance from Earth to the Sun, is about 150 million miles (241 million km). At this distance, Venus orbits the Sun in 874 days, while Mercury completes an orbit in 59 days. This means that if Venus was closer than Earth, then Mercury would be outside Earth's orbit; if Venus was further away than Earth, then Mercury would be inside Earth's orbit.
The math here shows us that if Mercury were a star, it would be too close to the Sun for its atmosphere to remain liquid water, which means that it would either be completely evaporated or frozen over. In fact, the average temperature on Mercury is 450 degrees Fahrenheit (230 degrees Celsius). It is so hot that any water that did exist would be solid under normal conditions.
This doesn't mean that there isn't water under Mercury's surface. Spacecraft have found signs of hydrous minerals, which are known to form under certain conditions such as high pressure and low temperatures. It may be possible that if enough water ever pooled together, it could become fluid again at these temperatures.
Mercury's symbol Hg is derived from its Greek name, hydrargyrum, which means "liquid silver" in reference to its gleaming surface. Because of its speed, the element is sometimes known as "quicksilver." Mercury, named after the solar system's fastest-moving planet, has been known to humans for millennia. It was first isolated by the Persian scientist Abd al-Rahman Ibn Bahaa ad-Din al-Jazari in 1172 and identified as a new chemical element about 50 years later. Modern scientists agree that mercury is an essential part of the global cycling of nutrients.
Mercury is a heavy metal that can cause serious health problems if it enters the human body through the skin or via the air we breathe. Exposure to elemental mercury occurs when it enters our environment either naturally (such as volcanic eruptions) or through human activities (such as mining, drilling, or chlor-alkali manufacturing). The most common source of exposure for adults is eating fish that have bioaccumulated mercury, such as tuna, swordfish, and shark. In addition, burning coal contains mercury. Industrial emissions also enter the atmosphere during the production of liquid organic chemicals and pesticides, among other things. The main route of exposure for children is through ingestion of household products containing mercury, such as thermometers, fluorescent light bulbs, and barometers.