Pluto:
The Ice Planet
Pluto, the only planet not visited by a space probe. Pluto was discovered in the 20th century. It is the ninth planet in order from the sun. The average distance of this planet from the sun is 5.91 billion km or 3.67 billion miles, which makes it the farthest planet from the sun. The rotation of this planet is about 6 Earth days and its revolution is about 248 Earth years. Pluto has a diameter of about 2,274 km or 1,413 miles and is the smallest planet. Its axial tilt is 98.8 degrees. Earth's mass is 454 times as great as Pluto's. The average surface temperature is between -228 degrees and -238 degrees Celsius (-378 degrees and -396 degrees Fahrenheit). The thin, frigid atmosphere is made up of methane and nitrogen. Pluto has one moon, Charon and no rings.
