The universe continues to puzzle and amaze people. Its vastness is immeasurable and its cause of creation is uncertain. Much of the information astronomers have collected about the solar system is about the four planets closest to the sun. Though no man has visited these planets, probes and telescopes have helped collect valuable information.

As the closest planet to the sun, Mercury has a surface temperature that can reach 840 degrees Fahrenheit. The planet doesn't have an atmosphere to trap heat, so the nighttime temperature can plummet to minus 275 degrees Fahrenheit. Despite it's extremely hot daytime temperature, astronomers suspect ice is located deep in its craters. These craters were the result of massive meteorites striking the surface throughout Mercury's billions of years in existence. Mercury is slightly smaller than the Earth's moon and is the smallest planet in this solar system.

Venus is near Earth and is the second closest planet to the sun. While viewing it from Earth, it is the brightest planet in this solar system. Prior to American and Russian probes soaring to Venus in the 1970s, astronomers thought the surface was full of vegetation, though that was difficult to tell due to the vast cloud cover. The surface temperature is the same as Mercury, at 840 degrees Fahrenheit. This temperature is attributed to a high carbon dioxide level caused by the greenhouse effect.

Earth is the only planet known to support life and is the third closest planet to the sun. Oceans cover approximately 70 percent of the planet's surface. The rest is covered by land, which was created from hardened lava that spewed out of the hot core billions of years ago. Earth features four seasons, which are the result of its axis of rotation that tilts more than 23 degrees. A protective atmosphere allows the Earth to trap in the sun's heat and block out harmful radiation.

As the fourth planet from the sun, Mars is much colder than Earth. It has an average surface temperature of minus 80 degrees Fahrenheit, though temperatures can rise to 20 degrees Fahrenheit at its equator in the summer. Mars is a bright rusty color, which is attributed to its iron-rich surface. Though Mars is about half the diameter of Earth, both planets have the same amount of dry land. The planet supports ice, though liquids can exist for a brief period.