As of 2008, the IAU has classified five celestial bodies as dwarf planets. Two of these, Ceres and Pluto, are known to qualify as dwarf planets through direct observation. The other three, Eris, Haumea, and Makemake, are thought to be dwarf planets from mathematical modeling—or in the case of Eris, because it is larger than Pluto—and qualify for the classification under IAU naming rules based on their magnitudes.[7][28]
- Ceres
– discovered on January 1, 1801 (45 years before Neptune), considered a planet for half a century before reclassification as an asteroid. Classified as a dwarf planet on September 13, 2006.
- Pluto
– discovered on February 18, 1930, classified as a planet for 76 years. Reclassified as a dwarf planet on August 24, 2006.
- Eris – discovered on January 5, 2005. Called the "tenth planet" in media reports. Accepted as a dwarf planet on September 13, 2006.
- Makemake – discovered on March 31, 2005. Accepted as a dwarf planet on July 11, 2008.
- Haumea – discovered on December 28, 2004. Accepted as a dwarf planet on September 17, 2008.
No space probes have visited any of the dwarf planets. This will change if NASA's Dawn and New Horizons missions reach Ceres and Pluto, respectively, as planned in 2015.[34][35] Dawn is also slated to orbit and observe another potential dwarf planet, Vesta, in 2011.
| Orbital attributes of dwarf planets[36] | |||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| Name | Region of Solar System | Orbital radius (AU) | Orbital period (years) | Mean orbital speed (km/s) | Inclination to ecliptic (°) | Orbital eccentricity | Planetary discriminant | ||||
| Ceres | Asteroid belt | 2.77 | 4.60 | 17.882 | 10.59 | 0.080 | 0.33 | ||||
| Pluto | Kuiper belt | 39.48 | 248.09 | 4.666 | 17.14 | 0.249 | 0.077 | ||||
| Haumea | Kuiper belt | 43.34 | 285.4 | 4.484 | 28.19 | 0.189 | ? | ||||
| Makemake | Kuiper belt | 45.79 | 309.9 | 4.419 | 28.96 | 0.159 | ? | ||||
| Eris | Scattered disc | 67.67 | 557 | 3.436 | 44.19 | 0.442 | 0.10 | ||||
| Physical attributes of dwarf planets | |||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Name | Equatorial diameter relative to the Moon | Equatorial diameter (km) | Mass relative to the Moon | Mass (×1021 kg) | Density (g/cm3) | Surface gravity (m/s2) | Escape velocity (km/s) | Axial inclination | Rotation period (days) | Moons | Surface temp. (K) | Atmosphere | |
| Ceres[37][38] | 28% | 974.6±3.2 | 1.3% | 0.95 | 2.08 | 0.27 | 0.51 | ~3° | 0.38 | 0 | 167 | none | |
| Pluto[39][40] | 69% | 2306±10 | 17.8% | 13.05 | 2.0 | 0.58 | 1.2 | 119.59° | -6.39 | 3 | 44 | transient | |
| Haumea[41][42] | 33% | 1150+250 −100 | 5.7% | 4.2 ± 0.1 | 2.6–3.3 | ~0.44 | ~0.84 | 2 | 32 ± 3 | ? | |||
| Makemake[41][43] | 43% | 1500+400 −200 | ~5%? | ~4? | ~2? | ~0.5 | ~0.8 | 0 | ~30 | transient? | |||
| Eris[4][41] | 75% | <2340 | 22.7% | 16.7 | 2.3 | ~0.8 | 1.3 | ~0.3 | 1 | 42 | transient? | ||
No comments:
Post a Comment