Mercury is the closest planet to the Sun. It is very similar to Earth's Moon. Its surface is very old and shows no sign of volcanic activity. It has no atmosphere and the surface is covered in dust. This view of the heavily cratered surface was taken by Mariner 10.
NASA
Mercury is the closest planet to the Sun. Since it is between the Earth and the Sun, it can be seen going through phases. Mercury is in its gibbous phase in this false-color image.
NASA
Mercury is a small, rocky planet. It has a large core. A huge rock weighing billions of tons may have smashed into Mercury early in its history. The collision might have blown off part of the shell of the planet. That could be why the mantle and crust of Mercury are so thin. This view of Mercury by Mariner 10 shows a surface covered with craters.
NASA
Mercury was very hot when it formed. Also, it is very near the Sun. The intense heat caused Mercury to lose the gases that would have created an atmosphere. This image of Mercury by Mariner 10 shows the southwest region of the planet. The largest craters seen in this picture are about 62 miles (100 km) in diameter.
NASA
This movie simulates Mercury's early history. Thousands of meteors falling toward the Sun crashed into Mercury. During this time Mercury's interior was being formed. Iron and other metals melted. The weight of this material pulled it to the center. Mercury's iron-nickel core is the densest in the solar system. It takes up almost three quarters of the diameter of the planet. As the core got larger, magma pushed through the cracks that opened in the surface, forming smooth planes. Mercury has a thin mantle and an even thinner crust. Because of its dense core and thin crust Mercury is like a large metal ball dipped in mud.
NASA
This image by Mariner 10 shows an area on Mercury called the Caloris Basin. The Caloris Basin has a diameter of about 800 miles (1300 km).
University of Arizona/SEDS
This close up image of the Caloris Basin was taken by Mariner 10. Its shows fractures and ridges on the planes. This area, like the rest of Mercury, is heavily cratered. Mercury is much closer to the Sun than Earth is. Daytime temperatures on Mercury can reach 870¬°F (467¬°C). Without an atmosphere to hold the heat, nighttime temperatures can drop to -280¬°F (-183¬°C).
Jet Propulsion Laboratory/NASA
This close-up view of Mercury shows some of its craters in detail. It shows a small bright halo crater in the center. This crater is six miles (10 km) in diameter. The large crater on the left has a diameter of 19 miles (30 km). The darker area (upper left) may be an ancient lava flow.
NASA
This is a close-up image of Mercury. Craters and scarpes are visible. The scarpes, sometimes called rupes, are the dark lines. They were probably formed early in the planet's history. As Mercury cooled and became a solid, the planet shrank. Then the crust contracted forming the rupes. Small craters continue to be made on the surface. The impacts that form them create a layer of dust that covers the planet.
NASA
This is an image of the Santa Monica rupes taken by Mariner 10. Rupes, or scarps, can extend as far as 300 miles (480 km) across the surface. The scarps are the dark lines running diagonally through this image. They cut through the crater in the center of the image. The contraction of the surface as the planet cooled and shrank produced the scarps and wrinkles that are visible.
NASA
Mercury orbits between the Sun and the Earth. It passes directly between the Earth and Sun thirteen times a century. In this X-ray image Mercury can be seen transiting the Sun. The image on the right is a series of eight photographs taken during the transit. The very small red dot in each of the images in the series is Mercury.
S. Freeland, H. Hudson/Yohkoh/Lockheed
The Surveyor spacecraft were a series of unmanned lunar landers. They were the first craft to land on the Moon. Surveyor 7 took the first photo of Mercury from the lunar surface. This photograph shows an unmanned lunar lander.
Jet Propulsion Laboratory/NASA
Mariner 10 was launched in November 1973. In February 1974, it passed near Venus on the way to Mercury. The gravity of Venus was used to propel Mariner 10 toward Mercury. It passed Mercury and entered an orbit around the Sun. As it orbited the Sun, it took photos of Mercury. It photographed Mercury on three successive passes before its instruments went dead.
