Uranus Diameter 4DE Rotation Period 17.25 hours Orbital Period 84 years Distance from Sun 19.2AU Orbit Eccentricity 0.05 Tilt 98 degrees! Temperature -201C Atmosphere hydrogen, helium and methane Gravity 1.15g Moons >21 Visits 1 Voyager 2 Uranus is the first planet to be discovered relatively recently. It was discovered by William Herschel in 1781. It is an unusual planet as it spins lying down. All of the other planets have a roughly vertical spin-axis (within 30 degrees or so), but Uranus’ spin axis is horizontal. Uranus has bands like Jupiter and Saturn, but they are so faint that they can’t be seen in optical light, only in the infra- red. Uranus’ moons are all named after characters in the works of Shakespeare and Pope. There are more being discovered at regular intervals. Uranus also has very faint rings made of a much darker material than Saturn’s.

Voyager 2 views of Uranus

Principle Moons of Uranus Miranda (500 km) Umbriel (1200 km) Ariel (1200 km) Oberon (1500 km) Titania (1600 km)

Miranda Miranda is a very interesting moon cos it just looks weird. You can tell from it’s appearance that something is definitely not right! We now believe that earlier in the life of the SS, Miranda was hit by something very big, which completely broke up the moon. Miranda then re-formed, but the pieces all fell back down in a random order, so parts of the moon that were on the inside are now visible on the outside, giving the surface a very mis-matched appearance.

Neptune Diameter 3.98DE Rotation Period 16 hours Orbital Period 165 years Distance from Sun 30.058AU Temperature -180C Atmosphere hydrogen, helium and methane Orbit Eccentricity 0.01 Tilt 29 degrees Gravity 1.194g Moons 8 Visits 1 Voyager 2 Neptune has the highest winds in the SS, reaching speeds of over 2000kph. At the time of Voyager 2’s visit it had a dark spot, similar to Jupiter’s Great Red Spot, which had disappeared by the time HST looked at the planet in 1994. Recent observations have shown that it now has another dark spot in the Northern hemisphere. Like the other Jovian planets, Neptune also has rings, but they are incredibly faint.

1989 – Voyager 2 Discovers Neptune's Rings

Triton Triton is the only large moon to orbit backwards. It could not have formed this way, so must have been captured, maybe from the Kuiper belt. The surface is relatively young with few craters. It is extremely cold – only –235C, so cold that methane, nitrogen and carbon dioxide freeze solid. The really interesting feature is its ice volcanoes, which probably erupt liquid nitrogen, dust or methane. Triton is v similar to Pluto and Neptunes pluto-crossing orbit suggests there may be a common history? Was pluto once a moon of Neptune or did triton use to be an independent planet? Also neried – the most highly elliptical orbit in the SS. 1.3m km to 9.6m km. Sim background? Collision with Triton during capture? Another, now- destroyed moon which perturbed/collided with Triton? 2700 km

Has ice volcanos that produce geysers of liquid nitrogen Triton's Polar Cap The only large moon with a retrograde orbit (captured Kuiper Belt object?) Has ice volcanos that produce geysers of liquid nitrogen