Since prehistoric times people have known the Sun, the Moon and five planets. The rest of the Solar System had to await discovery by people with telescopes. How many of the discoverers can you identify? For each discovery, choose the discoverer from the three names given. You can then check your answers, and also find out a bit more about them.

Quiz: Solar System Discoveries

1. Discovered the four largest moons of Jupiter in the 17th century: (A) Tycho Brahe; (B) Nicolaus Copernicus; (C) Galileo Galilei


2. Discovered Saturn's largest moon Titan: (A) Galileo Galilei; (B) Jean Dominique Cassini; (C) Christiaan Huygens


3. Discovered four of Saturn's moons and a division in the rings: (A) Jean Dominique Cassini; (B) William Lassell; (C) Christiaan Huygens


4. Discovered the Planet Uranus: (A) William Lassell; (B) William Herschel; (C) Urbain LeVerrier


5. His mathematical calculations led to the discovery of a new planet in 1846: (A) Urbain LeVerrier; (B) Johann Galle; (C) John Couch Adams


6. Used the mathematical predictions he received to find Neptune: (A) John Couch Adams; (B) John Herschel; (C) Johann Galle


7. Discovered Neptune's biggest moon Triton soon after the planet's discovery: (A) William Herschel; (B) William Lassell; (C) John Herschel


8. Discovered the moons of Mars, Deimos and Phobos: (A) Clyde Tombaugh; (B) Asaph Hall; (C) Edward Pickering


9. Discovered the dwarf planet Ceres: (A) Giuseppe Piazzi; (B) Johann Galle; (C) Johann Bode


10. Discovered Pluto: (A) Edwin Hubble; (B) Gerard Kuiper; (C) Clyde Tombaugh

Answers and notes

1. Discovered the four largest moons of Jupiter in the 17th century: (C) Galileo Galilei
Galileo (1564-1642) was one of the first to use a telescope to view the heavens. Early in January 1610 he discovered the four Jovian moons now known as the Galilean moons. The very first moons discovered orbiting another planet were a sensation, and undermined the prevailing assumption that everything revolved around the Earth.

2. Discovered Saturn's largest moon Titan: (C) Christiaan Huygens
Huygens (1629-1695) was a Dutch mathematician and scientist. Astronomers used to think Titan was the biggest moon in the Solar System, but space probe data show that Ganymede is slightly larger. The European Space Agency (ESA) sent a lander to Titan in 1997 – it was named Huygens in honor of the moon's discoverer.

3. Discovered four of Saturn's moons and a division in the rings: (A) Jean Dominique Cassini
Cassini (1625-1712) was the director of the Paris Observatory and an astronomer and surveyor. He made extensive studies of Saturn and was the first to realize there's a gap in the rings. It's now known as the Cassini division. NASA's mission to the Saturnian system was named Cassini and it carried the Huygens lander with it.

4. Discovered the Planet Uranus: (B) William Herschel
The first person ever to discover a new planet was German/English astronomer William Herschel (1738-1822). Observing in the back garden of his home in Bath, England, he noted something that seemed to be a comet. However it was a new planet, one so far from the Sun that it doubled the diameter of the known Solar System.

5. His mathematical calculations led to the discovery of a new planet in 1846: (A) Urbain LeVerrier
The orbit of the planet Uranus didn't quite match what was expected from Newtonian gravitation. A possible explanation was that an unknown planet beyond Uranus was disturbing its orbit. French mathematician Urbain LeVerrier (1811-1877) calculated where he thought this planet should be. He sent the calculations to the Berlin Observatory, and Johann Galle found the planet that night. English astronomer John Couch Adams had, independently, done similar calculations, but Cambridge Observatory didn't find anything.

6. Used the mathematical predictions he received to find Neptune: (C) Johann Galle

7. Discovered Neptune's biggest moon Triton soon after the planet's discovery: (B) William Lassell
After the discovery of Neptune was announced, John Herschel suggested that his friend William Lassell (1799-1880) look for a moon. Only 17 days after the planet was discovered, Lassell had discovered Triton. Astronomers think that Triton is a captured Kuiper Belt object with similarities to Pluto.

8. Discovered the moons of Mars, Deimos and Phobos: (B) Asaph Hall
Asaph Hall (1829-1907) was an American astronomer at the US Naval Observatory. He discovered the tiny Martian moons in August 1877. Mars was the god of war, and his sons Deimos and Phobos represented Terror and Panic.

9. Discovered the dwarf planet Ceres: (A) Giuseppe Piazzi
Piazzi discovered a planet in the place where Bode's Law predicted there should be one. But when other objects were discovered in similar orbits, astronomers decided this was a new class of object, and they were all called asteroids. In 2006 Ceres was judged to be big enough to be a dwarf planet.

10. Discovered Pluto: (C) Clyde Tombaugh
Tombaugh (1906-1997) was a young American astronomer hired by Lowell Observatory in Arizona. It had seemed that Neptune's orbit was being disturbed like the orbit of Uranus, and Percival Lowell (1855-1916) was convinced that there was another giant planet out there. He called it Planet X, and everyone assumed that Tombaugh had found it when he discovered Pluto. However it became clear that Pluto was way too small to have any gravitational effect on Neptune.

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