Solar System

 The Sun and everything that orbits the Sun, including the planets and their satellites; the dwarf planets, asteroids, Kuiper Belt Objects, and comets; and interplanetary dust and gas. The term may also refer to a group of celestial bodies orbiting another star.

Sun  The Sun is the star at the center of the Solar System. It is a nearly perfect sphere of hot plasma. It is by far the most important source of energy for life on Earth.

Terrestrial planet  The inner four worlds are called “terrestrial planets,” because, like Earth, their surfaces are all rocky.

Mercury  The closest planet to the sun, Mercury is only a bit larger than Earth's moon. Mercury has virtually no atmosphere to absorb meteor impacts, so its surface is pockmarked with craters, just like the moon.

Venus  Venus is terribly hot, even hotter than Mercury. The atmosphere is toxic. The pressure at the surface would crush and kill you. Scientists describe Venus’ situation as a runaway greenhouse effect. Its size and structure are similar to Earth.

Earth  The third planet from the sun, Earth is a water world, with two-thirds of the planet covered by ocean. It’s the only world known to harbor life. Earth’s atmosphere is rich in life- sustaining nitrogen and oxygen.

Mars  The fourth planet from the sun, is a cold, dusty place. The dust, an iron oxide, gives the planet its reddish cast. Mars shares similarities with Earth: It is rocky, has mountains and valleys, and storm systems.

Jovian planet  The four large outer worlds Jupiter, Saturn, Uranus, and Neptune are known as the “Jovian planets” (meaning “Jupiter- like”) because they are all huge compared to the terrestrial planets. All four contain mostly hydrogen and helium.

Jupiter  Jupiter is huge and is the most massive planet in our solar system. It’s a mostly gaseous world. A big feature is the Great Red Spot, a giant storm which has raged for hundreds of years. Jupiter has a strong magnetic field, and with dozens of moons, it looks a bit like a miniature solar system.

Saturn  Sixth planet in order of distance from the Sun, and the second largest in our solar system. Saturn’s most distinctive feature is a giant system of rings that surrounds the planet at its equator, stretching over twice the width of the planet itself.

Uranus  Uranus is an oddball. It’s the only giant planet whose equator is nearly at right angles to its orbit it basically orbits on its side. Astronomers think the planet collided with some other planet-size object long ago, causing the tilt.

Neptune  The eighth planet from the sun, Neptune is known for strong winds sometimes faster than the speed of sound. Neptune is far out and cold. Neptune is about 17 times as massive as Earth.