95 years ago today, on February 18, 1930 (January 20, 1930 in the lunar calendar), a newly discovered planet beyond Neptune was named Pluto. On February 18, 1930, Colette Dorp of the Royal Observatory in the United States discovered the ninth planet in the solar system. A British girl proposed naming it "Pluto". It was the last planet discovered in the solar system. The revolution period is 249 years. Ground observations show that Pluto's surface is covered with solid methane and it has a thin atmosphere. As Pluto moves away from the sun, this thin layer of gas will gradually solidify on the surface. NASA plans to launch a spacecraft to Pluto in 2001, allowing scientists to study the distant planet before its atmosphere freezes. Pluto was discovered to have a satellite (Charon) in 1978. The moon's surface appears to be different from Pluto, its surface appears to be covered with more ice than solid methane. Because its orbit is fixed by Pluto's gravity, the two always face each other in the same hemisphere. Since no spacecraft has visited Pluto, it remains a mysterious planet. Because Pluto is so far away from the sun, its surface temperature is almost close to minus 240 degrees Celsius. In 2006, it was excluded from the nine planets in the solar system.