User:Alastor Moody/Dwarf planet
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Since the discovery of Pluto in 1930, Pluto has widely been known to be considered as the ninth planet of the solar system. But in August 2006, astronomers and members from the International Astronomical Union (IAU) decided to re-define the term, "planet". The result ended up with Pluto demoted from planetary status to a "dwarf planet".
The term, "dwarf planets" is an official category making the boundary of the difference between a planet and a small solar system body. A celestial objects to be a dwarf planet must...
- Is in orbit around the Sun.
- Is not a satellite of a planet, or other nonstellar body.
- Does not produce energy by nuclear fusion.
- Has sufficient mass so that it assumes a hydrostatic equilibrium (nearly round) shape.
- Has not "cleared the neighborhood" around its orbit.
[edit] List of Dwarf Planets
The current dwarf planets are Pluto (a former planet), Ceres, and 136199 Eris.
Name | 1 Ceres | Pluto | Eris |
---|---|---|---|
Region of Solar system | Asteroid belt | Kuiper belt | Scattered disc |
Category | Asteroid | Plutino | Scattered disc object |
Diameter | 975×909 km | 2306±20 km | 2400±100 km |
Mass in kg compared to Earth |
9.5Template:E kg .00016 |
~1.305Template:E kg .0022 |
~1.5Template:E kg (est.) |
Mean equatorial radius* in km |
0.0738 471 |
0.180 1,148.07 |
0.19 ~1,200 |
Volume* in km3 |
0.00042 |
0.005 |
0.007 |
Density (in g/cm3) | 2.08 | 2.0 | |
Equatorial gravity (in m/s2) | 0.27 | 0.60 | |
Escape velocity (in km/s) | 0.51 | 1.2 | |
Rotation period (d) (in sidereal days) |
0.3781 | -6.38718 (retrograde) |
|
Orbital radius* (AU) mean mean in km |
2.5-2.9 2.766 413,715,000 |
39.5 39.48168677 5,906,376,200 |
37.77-97.56 67.6681 10,210,000,000 |
Orbital period*(a) (in sidereal Years) |
4.599 | 248.09 | 557 |
Mean orbital speed (in km/s) |
17.882 | 4.7490 | 3.436 |
Orbital Eccentricity | 0.080 | 0.24880766 | 0.44177 |
Orbital inclination | 10.587° | 17.14175° | 44.187° |
Inclination of the equator from the orbit (see Axial tilt) |
4° | 119.61° | |
Mean surface temperature (in K) | 167 | 40 | 30 |
Number of moons | 0 | 3 | 1 |
[edit] External links
- NPR: Dwarf Planets May Finally Get Respect (David Kestenbaum)
- SPACE.com: Q&A: The IAU's Proposed Planet Definition 16 August 2006 2:00 am ET
- BBC News: Q&A New planets proposal Wednesday, 16 August 2006, 13:36 GMT 14:36 UK
The Solar System |
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Star: The Sun |
Planets: Mercury - Venus - Earth - Mars - Jupiter - Saturn - Uranus - Neptune |
Dwarf planets: Ceres - Pluto - 2003 UB313 |
Other: Moon - Asteroid belt - Comets - Kuiper belt - Scattered disc - Oort cloud |
See also astronomical objects and the solar system's list of objects, sorted by radius or mass. |