The inner solar system comprises of four planets, Mercury, Venus, Earth, and Mars.

Mercury

The closest planet to the Sun, Mercury is 48 million miles away from the Earth at its closest point in orbit. It is a mere 28.6 million miles away from the Sun at its closest point in orbit. Mercury orbits the Sun every 88 days and rotates around its axis every 58.65 days. Temperatures can range from -300 degrees Fahrenheit to 800 degrees Fahrenheit. Closely resembling the moon, the surface of Mercury is marked by craters from billions of years of cosmic collisions.

Venus

Similar in size to Earth, and therefore called Earth's "Sister Planet," Venus is 25 million miles away from the Earth. Its orbit is the most circular of all the planets; it is 67 million miles from the Sun at its closest point and 68 million miles away from the Sun when it's at its farthest point, a mere 1 million mile difference. Venus takes about 243 Earth days to make one rotation about it's axis. The amount of time it takes to revolve around the Sun is less than that: about 226.3 days. This means daytime in Venus lasts for about 115 days, allowing temperatures to rise. Temperatures on Venus average about 867 degrees Fahrenheit. The surface of Venus is blocked by a dense atmosphere consisting of Carbon monoxide. Clouds of sulfuric acid are highly reflective, making Venus the brightest object in the night sky, save for the Moon.

Earth

Our home planet, Earth, is the largest of the inner planets. It ranges from between 91 and 94.5 million miles away from the Sun during its orbit. Temperatures range from -128 degrees Fahrenheit to 136 degrees Fahrenheit. From space, the Earth looks blue and white. The surface of the Earth is marked by large oceans and smaller land segments called tectonic plates.

Mars

Mars is about 35 million miles away from the Earth and ranges from 128 million miles and 155 million miles away from the Sun. Its day is similar to that of the Earth at about 24.6 hours and takes the equivalent of 1.88 Earth years to orbit the Sun. Also known as the "Red Planet" due to the layer of iron oxide covering the planet, Mars also marked by a number of craters. However the atmosphere of Mars prevents as many impacts as we see on the Moon. This atmosphere is very thin and subjects Mars to the harsh solar winds.

For more information on the solar system, visit www.Space.com

For more information on the universe, visit www.NASA.gov