Uranus and Neptune: The True Twins of the Solar System

1. Uranus Neptune And their moons

2. Uranus Statistics Radius: 3.98 times Earth’s (25,559 km) Mass: 14.54 times Earth’s (8.68 x 10^25 kg ) Density: 1.32 g/cm³ ( 23 % of Earth’s) Surface Gravity: 8.69 m/s² (88.6 % Earth’s) Orbit and Rotation Radius (average.): 19 AU (2,749,000,000 km ) Year: 84 Earth Years Sidereal Day: 17.24 Hours Axial Tilt: 97.86º (Earth’s: 23.45°)

3. Neptune’s Statistics Radius: 3.81 times Earth’s (24,764 km ) Mass: 17.13 times Earth’s (1.02 x 10^26 kg ) Density: 1.64 g/cm³ ( 30 % of Earth’s) Surface Gravity: 11.15 m/s² ( 114% Earth’s) Orbit and Rotation Radius (average.): 30.06 AU (4,496,000,000 km ) Year: 164.8 Earth Years Sidereal Day: 16.11 hours Axial Tilt: 29.56º (Earth’s: 23.45°)

4. Uranus and Neptune True Twins They are gas giants like Jupiter made mostly of Hydrogen and its compounds, chiefly H2O. About the same size color and structure, Uranus and Neptune are true twins. But both have large amounts of methane in their atmosphere that absorb red making them appear blue Their interiors have a large layer of compressed water around their cores.

5. Effects of Uranus’ Tilton the path of the Sun For a person at a Pole the “daytime” (or summer) lasts 42 Earth years When summer begins the Sun rises circles just above the horizon, then for 21 years it gradually circles higher and higher. Finally it follows a circle about 8° from Zenith. Then it spirals out, in larger and larger circles for 21 more years It only sets because of the change of seasons, and night (or winter) lasts another 42 years!

6. Why Uranus is Monochrome and Tilted As a result of the extreme tilt all of Uranus has its turn with an overhead Sun The resulting unusually even solar heating of the atmosphere may explain the lack of cloud bands found on the other gas giants. Uranus’s extreme tilt is thought to be due to either: • a collision with a large planetismal or • the Gravity of nearby planets, mostly Saturn.

7. Uranus was unknown to the ancients. It was discovered by Sir William Herschel in 1781 though at first he thought it was a comet Uranus has a complex ring system like Saturn But thinner. In 1789 Herschel first saw a ring but was unsure. In 1977 the rings were confirmed to exist Uranus Discovery and Rings

8. It has at least 27 Moons, Including five larger ones The two largest Titania and Oberon were discovered by Herschel The Fifth largest, Miranda seems to have been shattered and then been reassembled Only 472 km in radius it has a giant cliff 15 km high! That’s like one about 203 km (122 miles) high on Earth! Uranus’ Moons

9. The Discovery of Neptune Neptune was unknown to ancients. Galileo saw it in 1613 while looking at Jupiter’s moons but didn’t know what it was In the 1840’s two astronomers noticed a perturbation, that is a slight change in Uranus’ orbit due to the gravity of an undiscovered planet. One was English …one French. A German using the French calculations spotted it in 1846. For decades both France and England claimed credit for the discovery

10. Neptune is a denser version of Uranus. It has thin rings It has more methane in its atmosphere making it a deep blue. As it has a normal axial tilt it has faint cloud bands Winds on Neptune are particularly fast 2200 km/h! …powered by an internal heat source. That also makes it emit more heat than it gets. Like Jupiter it has a large long lasting storm The Great Dark/Blue Spot. Neptune

11. Neptune has at least six small moons. The largest, Triton orbits “backward” And is probably a captured Dwarf planet from the Kuiper belt. It has a “wrinkled” cantaloupe-like terrain. Geysers of nitrogen, water ice and carbon driven by the Sun’s heat leave dark streaks like soot. Voyager detected such an eruption Triton and other Moons