The Romans believed that gods and goddesses were in charge of everything on Earth. Mercury is named after the messenger for their gods. The Roman Mercury had wings on his helmet and shoes. He could travel very quickly from place to place. The planet Mercury moves quickly around the sun. That is how it got its name.
Mercury is a little bigger than Earth's moon. It is made of heavier materials, like iron. But if you could weigh Mercury and the moon, Mercury would weigh a lot more. Mercury is heavy, but it is small. It would take more than 18 Mercurys to be as big as Earth.
The surface of Mercury looks like Earth's moon. It is covered with holes. The holes are called impact craters. The craters were made by rocks falling from space. The rocks are going very fast when they hit Mercury. A hole is made where the rock hits. Earth has a blanket of air around it. Mercury does not. The blanket is what helps keep Earth from getting too hot or cold. Because it is so close to the sun, Mercury can be very hot. At night, Mercury gets very cold. We could not live on Mercury!
Mercury is hard to study because it is so close to the sun. People have never gone to Mercury. Spacecraft without people have gone. Mariner 10 was the first to visit Mercury. It flew by in 1974 and 1975. Not even half of Mercury was seen then. After that, nothing was sent to Mercury for more than 30 years. NASA's MESSENGER spacecraft flew by Mercury in 2008 and 2009. In March 2011, it began to orbit Mercury. MESSENGER will study parts of Mercury that have not been seen before. It will let scientists learn many new things about the planet.
Mercury....On the Inside
Researchers working with high-precision planetary radars, including the Goldstone Solar System Radar of NASA's Jet Propulsion Laboratory, Pasadena, Calif., have discovered strong evidence that the planet Mercury has a molten core. The finding explains a more than three-decade old planetary mystery that began with the flight of JPL's Mariner 10 spacecraft. The research appears in this week's issue of the journal Science.
Launched in Nov. 1973, Mariner 10 made three close approaches to Mercury in 1974 and 75. Among its discoveries was that Mercury had its own weak magnetic field - about one percent as strong as that found on Earth.
"Scientists had not expected to find a magnetic field at Mercury," said Professor Jean-Luc Margot of Cornell University, Ithaca, N.Y., leader of the research team. "Planetary magnetic fields are associated with molten cores, and the prevailing theory was the planet was too small to have a molten core."
Scientists theorized that Mercury consisted of a silicate mantle surrounding a solid iron core. This iron was considered solid - or so the theory went - because small planets like Mercury cool off rapidly after their formation. If Mercury followed this pattern, then its core should have frozen long ago.