Discoveries of the Outer Planets

  • Discovery of Jupiter's Large Moons

    In 1610, Galileo Galilei realized that Jupiter had 4 large moons orbiting it. They are Io, Europa, Ganymede and Callisto. This was an important discovery, because it demonstrated that Earth was not the center of the Universe as some believed.
  • Discovery of Sarurn's Rings

    In 1610, Galileo Galilei was the first to observe Saturn with a telescope. Because of the crudeness of his telescope, he couldn't figure out what Saturn's rings were. He guessed that there were two large moons on each side of Saturn. In 1659, Christiaan Huygens used an advanced telescope to determine that it was actually a ring system.
  • Discovery of Titan

    Titan is Saturn's largest moon and was the first of Saturn's moons to be discovered. It was discovered in 1655 Christiaan Huyens. It is the only moon known to have a dense atmosphere. It is also the only object other than Earth for which evidence of stable bodies of surface liquid has been found.
  • Discovery of the Great Red Spot

    Jupiter's neverending storm known as the Great Red Spot was discovered by Gian Domenico Cassini in 1665.
  • Discovery of Uranus

    Uranus was discovered by William Herschel in 1781. He originally thought it was a comet but realized it did not move like a comet. Neval Maskelyne suggested it could be a planet. Herschal named it Georgium Sidus but it was later renamed to Uranus.
  • Discovery of Triton

    Triton is the largest moon of the planet Neptune. It was discoverd by William Lassel in 1846. It is the only large moon with a retrograde orbit, which is an orbit in the opposite direction to its planet's rotation.
  • Discovery of Neptune

    Johann Galle and his student Heinrich d'Arrest discovered Neptune in 1864 within a degree of the position predicted by Urbain Le Verrier. Le Verrier is credited with the discovery. The first observation of Neptune were made by Galileo in 1612, but it was thought to be a star.
  • Discovery of Pluto

    Clyde Tombaugh discovered Pluto in 1930. He was continuing the search for a ninth planet started by Percival Lowell. Pluto was reclassified as a dwarf planet in 2006.
  • Discovery of The Great Dark Spot

    The Great Dark Spot is a series of dark spots on Neptune that are similar to Jupiter's Great Red Spot. The first one was seen in 1989 by NASA's Voyager 2. Like The Great Red Spot, it is a massive storm. The differnce is that that spots disappear and reform every few years.