Dwarf planet

From CreationWiki, the encyclopedia of creation science

Eris and its satellite, Dysnomia.

A dwarf planet is a satellite of the Sun that meets the following criteria now set by the International Astronomical Union:

“

(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 neighbourhood around its orbit, and (d)is not a satellite.^[1]

”

1 Pluto
2 Eris
3 Table
4 References

Pluto

Main Article: Pluto

The first of the dwarf planets ever discovered was Pluto. At the time, no astronomer thought to classify Pluto any differently from any other planet. Yet Pluto was always an anomaly among planets. Not only was it the smallest planet, but it was also a rocky or "terrestrial" planet in a region that ought to have only gas giants within it, according to the nebula hypothesis. Some astronomers even speculated that the Sun had captured Pluto from outside its system.

Eris

Main Article: Eris

The concept of "dwarf planet" properly dates to the discovery of the scatter-disk object named Eris on January 5, 2005. With the confirmation of the identification of Eris, a formal debate began on the subject of what does, and what does not, constitute a planet. The community of astronomers decided that relying on history and tradition simply would not serve. The eight celestial bodies that now remain under the present definition of planet do not share their orbits with any other objects. The objects now called dwarf planets do not have this distinction. And yet these objects are significantly heavier than mere asteroids, in that they are so heavy that their own weight, and more particularly their own gravity, forces them to assume the round or nearly-round shape that all planets have.

True-color image of Pluto

Eris has another distinction that forced the debate: it is more massive even than Pluto (by twenty-seven percent) and is therefore the heaviest dwarf planet yet found. The mass of Eris is inferred from the orbital parameters, including the apsides and period, of the small body that orbits Eris. If Pluto could still be called a planet, then Eris deserved that distinction as well.

In 2006, the International Astronomical Union settled the issue. They determined that Eris was not a planet, and neither was Pluto. But the criteria they set also provoked yet another reassessment of the status of Ceres, the largest and first-discovered object in the asteroid belt. Upon consideration, the IAU declared that Ceres was a dwarf planet as well.

Today the list of dwarf planets is limited to these three: Eris, Pluto, and Ceres.

Table

Ceres

List of all known dwarf planets, from the innermost to the outermost:

Name	Perihelion	Aphelion	Eccentricity	Sidereal year	Inclination	Mass	Sidereal day
Ceres	3807265791502.545 AU380,726,579.15 km 236,572,528.403 mi	4468488376902.987 AU446,848,837.69 km 277,658,995.025 mi	0.079760170.0798	1679.784754.599 a1,679.785 da	0.1847729813603910.587 °0.185 rad 11.763 grad	9.46E+200.0129 M☾9.46e+20 kg 1.583e-4 M⊕	32666.49.074 h0.378 da
Pluto	4436824591966.429.658 AU4.43682e+9 km 2.75691e+9 mi	737592789763249.305 AU7.37593e+9 km 4.58319e+9 mi	0.248807660.249	90614.8725248.09 a90,614.872 da	0.2991799770537417.142 °0.299 rad 19.046 grad	1.305E+220.178 M☾1.305e+22 kg 0.00218 M⊕	-551856.672-153.294 h-6.387 da
Eris	567424720910037.93 AU5.67425e+9 km 3.52581e+9 mi	1459028026110097.53 AU1.45903e+10 km 9.06598e+9 mi	0.440.44	203590.35557.4 a203,590.35 da	0.7707286710344444.16 °0.771 rad 49.066 grad	1.66E+220.226 M☾1.66e+22 kg 0.00278 M⊕	288008 h0.333 da

References

↑ "IAU0602: the Final IAU Resolution on the Definition of 'Planet' Ready for Voting," International Astronomical Union, 2005. Accessed January 14, 2008.

Browse

	The Solar System
Star	Sol
Planets	Vulcan • Mercury • Venus • Earth • Mars • Jupiter • Saturn • Uranus • Neptune
Dwarf Planets	Ceres • Pluto • Eris
Asteroid Belt	Major asteroids • C-type asteroids • S-type asteroids • M-type asteroids
Trans-Neptunian Objects	Kuiper belt • Scatter disk • Oort cloud • Nemesis
Moons	Terrestrial • Martian • Jovian • Saturnine • Uranian • Neptunian • Plutonian • Eridian
Featured moons	Moon • Phobos • Deimos • Io • Europa • Ganymede • Callisto • Mimas • Enceladus • Tethys • Dione • Rhea • Titan • Hyperion • Iapetus • Miranda • Ariel • Umbriel • Titania • Oberon • Triton • Nereid • Charon • Nix • Hydra • Dysnomia