There was not any good reason for the International Astronomical Union (IAU) to define the term "planet" as it did, or WHEN it did. There had never been a formal definition of the word "planet". The IAU defined "Planet" with three criteria;
1. Orbits a star, not another planet
2. Has reached hydrostatic equilibrium; meaning, its own gravity has squashed it into a spherical shape (or nearly so).
3. Has "cleared its orbit" of other objects, meaning that there are no other objects traveling in the same orbital path.
It is this third requirement that caused Pluto to be demoted from "planet" to "dwarf planet". There are other objects in the Kuiper Belt which potentially could match Pluto's orbit. In fact, by this third criteria, the Earth itself doesn't really qualify as a "planet"; there are near-Earth asteroids that orbit in paths that are not dramatically different from ours.
Part of the controversy has been that "recent" (at the time) discoveries of other Kuiper Belt objects which are larger than Pluto itself is. Haumea, Eris, and Makemake orbit further out from the Sun and are larger than Pluto. For that matter, the former asteroid Ceres is also larger than Pluto. All five of these objects are now called "dwarf planets".
It seems likely that the next meeting of the IAU will reconsider the status of Pluto, but there's no way of knowing what the decision will be. The IAU is open to any astronomer, but only the ones who attend the meetings get to vote; last time, about 3% of the members actually attended and voted.
it used to vary between neptune and Pluto due to plutos unusual orbit. but since Pluto was declared not a planet. it is neptune.
For 20 years of its 246 year orbit, Dwarf planet Pluto is closer to the sun than Neptune. So Neptune is futher out for a while. Since Plutos de-classification to a Dwarf planet though, Neptune now remains the furthest planet at all times.
The symbol for Pluto, the dwarf planet, is a capital letter "P" with a stylized representation of the god Pluto's helmet.
Plutoâ??s main feature is that it is a very cold planet because of its distance away to the sun with an average temperature of 375 degrees below zero. Also, even though it is no longer considered to be a planet, it still has a moon on it named Charon.
The temperature range of Pluto is 33 degrees Kelvin to 55 degrees Kelvin.
god of the underworld
Plutos not a planet because is does not meet the necessary requirements to be a planet
Neptune's, at times.
comet
Neptune. but since plutos demotion, it will always be the farthest planet from the sun as we know today.
pluto orbits around the sun faster than any planet
it used to vary between neptune and Pluto due to plutos unusual orbit. but since Pluto was declared not a planet. it is neptune.
Sedna is a dwarf planet. It is to far away to be one of plutos moons and is proved to orbit the sun
The duration of Are We Changing Planet Earth? is 3600.0 seconds.
No - he has since passed away. Pluto was discovered in 1930 by Clyde Tombaugh, who died in 1997, nine years before Plutos reclassification to a dwarf planet in 2006. Venetia Burney thought of the name for Pluto in 1930, when she was eleven. She died in 2009, so she would have known of Plutos reclassification.
Pluto only has one moon and i don't think it is even a moon its a dwarf planet along with Pluto
our planet changes by the seasons and the weather