why isn't pluto a planet anymore?

http://en.wikipedia.org/wiki/Pluto

Because Pluto's orbit crosses those of the other planets therefore makeing it ineligible to be a planet for not meeting certain standards that have been lain out.

Pluto is no longer considered a planet because of a change in the definition of planets by the International Astronomical Union (IAU) in 2006. According to the new definition, a planet is defined as a celestial body that orbits the Sun, is spherical in shape, and has cleared its orbit of other debris.

Pluto meets the first two criteria, as it orbits the Sun and is spherical in shape. However, it fails to meet the third criterion of clearing its orbit. Its orbit is not entirely free from other celestial bodies, as it crosses the orbit of Neptune and is surrounded by a region known as the Kuiper Belt, which contains many other small icy bodies.

As a result, the IAU reclassified Pluto as a "dwarf planet." This means that while Pluto shares similarities with planets, it does not meet the specific criteria to be categorized as one.

You can learn more about this topic and the specific details by visiting the Wikipedia page on Pluto (http://en.wikipedia.org/wiki/Pluto).