Archives: Fun and Games

Huge, icy Uranus is the seventh planet from the Sun and the third largest planet in our Solar System. Ancient observers thought that there were five planets plus the Earth, Sun and Moon. So when William Herschel discovered Uranus in 1781, it was the first time in modern history that another planet had been found.

Uranus and Neptune are often called the ice giants. The atmosphere on Uranus is like Neptune and both are different in composition to Jupiter and Saturn. The atmosphere on Uranus does contain hydrogen and helium but also ice, ammonia and methane. It is the methane that gives Uranus its blue-green colour. Uranus is the coldest planet in the Solar System, with a minimum temperature of –224°C (-371°F).

Uranus is the only planet whose equator is nearly at right angles to its orbit, so it appears to rotate on its side along its orbital path. Like Venus, Uranus rotates east to west and takes 84 Earth years to complete one orbit.

Uranus has 27 known moons all named after characters from the works of the famous authors Shakespeare and Pope. The five main moons are called Miranda, Ariel, Umbriel, Titania and Oberon. Miranda is the smallest of the five main moons and its surface is unlike any other moon we know, with a giant canyon twelve times deeper than the Grand Canyon.
Most of what we know about Uranus is due to the flyby of the Voyager 2 spacecraft in 1986. Uranus was named after the Greek god of the sky.

Neptune was discovered by the German astronomer Galle in 1846. The atmosphere on Neptune is like Uranus with hydrogen and helium but also ice, ammonia and methane. Methane and another unknown element give Neptune its bright blue colour. Neptune is more than 30 times further away from the Sun than the Earth. In 2011 Neptune completed its first 165-year orbit of the Sun since its discovery in 1846.

Most of what we know about Neptune is due to the flyby of the Voyager 2 spacecraft in 1989. Voyager 2 tracked an oval-shaped Great Dark Spot in Neptune’s southern hemisphere. This spot was a hurricane, large enough to contain the entire Earth, spinning anticlockwise and moving at almost 1,200km (750 miles) per hour.

Voyager 2 also discovered six of Neptune’s 13 known moons. Neptune’s largest moon, Triton, was discovered by William Lassell just 17 days after the discovery of Neptune. Triton orbits Neptune in the opposite direction to any other large planetary moon. This is probably because it was captured by Neptune’s gravitational force. It may once have been a dwarf planet in the Kuiper belt. Triton is the coldest object that has so far been measured in the Solar System, with surface temperatures of around –235°C (-391°F). Ice volcanoes on the surface of Triton shoot out liquid nitrogen, methane and dust, which freezes and falls back to the surface as snow. Voyager 2 took an image of an ice volcano shooting 8 km (5 miles) into the sky.
Neptune is named after the Roman god of the sea and its moons were named after other sea gods and nymphs from Greek mythology.

Beyond Neptune is a disc shaped area called the Kuiper belt named after the astronomer Gerard Kuiper. The dwarf planets Pluto and Eris lie in this far distant region of the Solar System.

From the 1930s, when it was classified, until 2006 Pluto was thought to be the ninth and smallest planet in the Solar System. But in 2005 Eris, which is 27% bigger than Pluto, was discovered deep inside the Kuiper Belt. In 2006 The International Astronomical Union decided that a new classification was needed and Pluto, Eris and the asteroid Ceres became the first dwarf planets. Haumea and Makemake are also now classified as dwarf planets.

In 2015 the New Horizons spacecraft, launched in 2008, became the first to visit Pluto and the Kuiper Belt.