NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute/Alex Parker, Public domainPluto
The demoted ninth planet that turned out to be a geologically alive world
Overview
Pluto is a dwarf planet in the Kuiper belt, a ring of bodies beyond the orbit of Neptune. It is the ninth-largest and tenth-most-massive known object to directly orbit the Sun. It is the largest known trans-Neptunian object by volume by a small margin, but is less massive than Eris, which is denser. Like other Kuiper belt objects, Pluto is made primarily of ice and rock and is much smaller than the inner planets. Pluto has roughly one-sixth the mass of the Moon and one-third of its volume. Originally considered a planet, its status was changed when astronomers adopted a new definition of the word with new criteria.
Source: Wikipedia
Why it matters
- Reclassified as a dwarf planet in 2006 after the discovery of Eris and other Kuiper belt objects.
- New Horizons (2015) revealed nitrogen-ice glaciers, mountains of water ice and the heart-shaped Sputnik Planitia.
- Its moon Charon is so large that the two orbit a point outside Pluto — effectively a double dwarf planet.
System
- Discovered
- 1930 · direct observation
- Discoverers
- Tombaugh, C. W.
- Star
- Sun · G2 V · 5,772 K · 1 M☉
- System
- 8 known planets
Orbit in the Solar System
| World | Period | Distance | Radius | Mass | Temp. |
|---|---|---|---|---|---|
| Mercury | 88 d | 0.387 AU | 0.38 R⊕ | 0.055 M⊕ | 440 K |
| Venus | 224.7 d | 0.723 AU | 0.95 R⊕ | 0.82 M⊕ | 737 K |
| Earth | 365.2 d | 1 AU | 1 R⊕ | 1 M⊕ | 288 K |
| Mars | 687 d | 1.52 AU | 0.53 R⊕ | 0.11 M⊕ | 208 K |
| Ceres | 4.6 yr | 2.77 AU | 0.07 R⊕ | 0.94 ×10²¹ kg | — |
| Jupiter | 11.9 yr | 5.2 AU | 1 R♃ | 1 M♃ | 163 K |
| Saturn | 29.4 yr | 9.57 AU | 0.84 R♃ | 95.11 M⊕ | 133 K |
| Uranus | 83.7 yr | 19.16 AU | 0.36 R♃ | 14.53 M⊕ | 78 K |
| Neptune | 163.7 yr | 30.18 AU | 3.88 R⊕ | 17.08 M⊕ | 73 K |
| Pluto | 247.9 yr | 39.48 AU | 0.19 R⊕ | 13 ×10²¹ kg | 48 K |
| Haumea | 282 yr | 43.1 AU | 0.12 R⊕ | — | 50 K |
| Makemake | 306.6 yr | 45.6 AU | 0.11 R⊕ | 3.1 ×10²¹ kg | — |
| Eris | 561.3 yr | 67.9 AU | 0.18 R⊕ | 17 ×10²¹ kg | 43 K |
| Sedna | 12,676.2 yr | 544 AU | 0.08 R⊕ | — | 12 K |
By the numbers
- Radius
- 0.19 R⊕1,187 km
- Mass
- 13 ×10²¹ kg0.01 ×10²⁴ kg
- Orbital period
- 247.9 yr
- Distance from Sun
- 39.48 AU5,906 million km
- Eccentricity
- 0.244elliptical
- Mean temperature
- -225 °C48 K
- Gravity
- 0.7 m/s²0.07 g
- Day length
- 153.3 h6.4 Earth days
- Moons
- 5
- Density
- 1.85 g/cm³
- Axial tilt
- 119.5°
Sources
Image: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute/Alex Parker, Public domain · Public domain · image page
Text: Wikipedia (CC BY-SA 4.0). Taglines and highlights are editorial.