It probably won't be revised for quite some time. The reason that Pluto fails as a major planet is because it has not "cleared its neighborhood. Pluto also shares its orbit with the Kuiper belt, a swath of small icy bodies beyond Neptune.
A moon is usually understood to be a natural body that orbits a planet, be it major e. Earth , minor e. Pluto , or extra-solar although no extra-solar moons have been detected at the time of this posting. However, the IAU has not yet formally defined a moon. Binary planets - Pluto and Charon are so close in mass that it is more accurate to say that they both more orbit a point in space between them, rather than Charon strictly orbiting Pluto. The term binary planet is now informal, but could become official some time in the future.
How round? The second bullet point in the IAU definition of a planet is that a planet must be in hydrostatic equilibrium, but at the smallest end of the planet spectrum, this gets a little bit blurry. They may have to attach some kind of number to it someday. Exoplanets As of right now, this only applies to our own Solar system, with "exoplanet" being an entirely separate category.
Aside from human prejudice for good ol' Sol, this is silly. There should be one, universal definition. Brown dwarfs New observations are making it clear that objects may exist ranging smoothly from Jupiter, an undisputed planet, right on up to objects that are indisputably stars. Where do we draw the line?
Nowhere is that mentioned. Transitional objects are fuzzily known as brown dwarfs. Trojan asteroids If you want to get really finicky about it, even Earth, Mars, Jupiter, and Neptune might not qualify as major planets, either. They all have a significant number of asteroids orbiting the Sun locked into orbital resonances at their orbital radii- they may be dominant at their radii, but some people grumble at the wording of the "cleared their neighborhood" criterion.
In fact, many known planets and other bodies in our solar system are in or have been in similar orbital resonances. Jupiter and Saturn are thought to have been in resonance in the past, and Jupiter's Galilean moons are in a resonance. Additionally, we know of extra-solar planets in multiple systems, such as the Kepler system, that are in resonance.
Planets are define as gravitationally round bodies that orbit the sun and have cleared their orbital region. Also see: Difference between dwarf planets and moons.
Image Courtesy: earthsky. Difference between Dwarf Planet and Planet. Key difference: A planet is an object that orbits the Sun in an elliptical orbit, has compounded its matter in a spherical shape and has cleared its orbit of other debris.
As per the IAU's final Resolution 5A, planets and other bodies, except satellites, in our Solar System can be defined into three distinct categories: A planet is a celestial body that a is in orbit around the Sun, b has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium nearly round shape, and c has cleared the neighborhood around its orbit.
A " dwarf planet " is a celestial body that a is in orbit around the Sun, b has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium nearly round shape, c has not cleared the neighborhood around its orbit, and d is not a satellite. All other objects, except satellites, orbiting the Sun shall be referred to collectively as "Small Solar System Bodies. Also see: Difference between planets and moons According to the previous categorization, all of the newly discovered trans-Neptunian objects would also be classified as planets, even though, like Pluto, they did not fit the traditional definition of a planet.
Add new comment Your name. Plain text. This question is for testing whether or not you are a human visitor and to prevent automated spam submissions. The inner planets, the closest to the Sun, are solid spheres of rock and include Mercury, Venus, Earth, and Mars. The inner planets were constantly bombarded by asteroids and meteorites during their first million years in existence. Consequently, you will find craters of varying sizes on the inner planets and their satellites.
The outer planets are large gaseous spheres with rings and include Jupiter, Saturn, Uranus, and Neptune. Between the inner and outer planets is an asteroid belt. Every planet, except for Earth, was named for an ancient Roman god or goddess.
Some of the planets have naturally occurring satellites, or moons, while others do not. All eight planets orbit the Sun in their own unique way. Dwarf planet is a new class of astronomical objects.
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