THE SOLAR SYSTEM
I grade school, we were taught that the solar system consists of the sun, nine planets, and their moons. It’s not that simple.
No one really knows how many planets there are because there is no settled scientific definition of a planet. All asyronomers agree upon the validity of the four terrestrial planets___ Mercury, Venus, Earth, and Mars___and the four gasseous giants___Jupiter, Saturn, Uranus, and Neptune___but arctic Pluto is a matter of great dispute.
Pluto is about two-thirds the size of our moon and takes 248 years to orbit the sun. The tiny ice planet travels in a strange elliptical orbit on a different plane than the other eight. Its coldness, distance from the other planets, and warped path around the sun has led many scientists to believe that it is really a comet in the Kuiper Belt, a region of ice debris on the outskirts of the solar system.
Pluto has a recently diacovered rival on the Kuiper Belt, a hunk of frozen rock officially referred to as 2003 UB313 but informally called Xena. The object is three farther from the sun than Pluto and has an even atranger 560-year orbit, tilted 45 degreesodf the plane of the reat of the planets. But 2003 UB313 is Larger than Pluto, and many acientista feel that if Pluto deserves to be called a planet, then it does, too.
ADDITIONAL FACTS
1.Two other Large frozen objects in the Kuiper Belt___ Quaoar and Sedna___are almost as big as Pluto. They may become the eleventh and twelfth planets.
2.Astronomer Michael E. Brown discovered 2003 UB313 and nicknamed it Xena after the TV show atarting Lucy Lawless as an ancient Greek warrior peincess. He hopes to make Xena the official name.
3.Our solar system has 153 known moons, but that number is highly contested.
4.Seven moons in the solr system are Larger than Pluto. This includes Jupiter’s Io, which has an atmosphere and active volcanoes.
Puzzle 