According to NASA, Mercury is considered a terrestrial planet, meaning it has a core, mantle and crust, much like Earth. Mercury's atmosphere contains oxygen, sodium, hydrogen, helium and potassium. More »

Like Earth, Mercury is one of four terrestrial planets. It is known as a terrestrial planet because it has a solid ground surface made up of rock and metal. This surface makes Mercury's density very similar to that of th... More »

There is not much known about Mercury or its surface, except that it is similar to the moon in appearance and its composition consists of primarily molecular oxygen, sodium and hydrogen. There are also small amounts of h... More »

Scientists believe phytoplankton in the Earth's oceans produce between 50 and 85 percent of the planet's oxygen. The exact figure is difficult to calculate because scientists do not know how much phytoplankton exists on ... More »

Scientists have hypothesized and made predictions about the cause of the Earth's magnetic fields, and the prevailing theory is that the Earth's magnetism originates from the planet's center, or core. Because scientists d... More » Science Physics

Mercury is the smallest planet in the solar system, and it is only slightly larger than Earth's moon. The closest planet to the sun, Mercury takes just 88 Earth days to complete a single orbit. More »

The Earth's core consists primarily of hot and solid iron and nickel. It is the innermost layer of the Earth and has a temperature of up to 13,000 degrees Fahrenheit. More » Science Earth Science Layers of the Earth