Quiz of the Day
Planets & the Solar System
Wednesday, 23 September 2026
Neptune was discovered on 23 Sep 1846 — an orbit through the planets, moons, dwarf planets and our solar system
1. Which planet orbits closest to the Sun?
- Mercury
- Earth
- Venus
- Mars
Mercury is the innermost planet, whipping around the Sun in just 88 Earth days. Despite being closest to the Sun, it is not the hottest planet because it has almost no atmosphere to trap heat. Its surface swings from scorching daytime highs to bitterly cold nights.
2. What is the largest planet in the solar system?
- Neptune
- Uranus
- Jupiter
- Saturn
Jupiter is so massive that it is more than twice as heavy as all the other planets combined. This gas giant is famous for the Great Red Spot, a storm larger than Earth that has raged for centuries. More than 1,300 Earths could fit inside it.
3. Which planet is commonly known as the 'Red Planet'?
- Jupiter
- Mars
- Venus
- Mercury
Mars looks red because its surface is covered in iron oxide, essentially rust. It is home to Olympus Mons, the tallest known volcano in the solar system, about two and a half times the height of Mount Everest. Two small moons, Phobos and Deimos, orbit the planet.
4. How many planets are officially recognized in our solar system today?
- 10
- 9
- 8
- 7
Since 2006 the solar system has had eight recognized planets. That year the International Astronomical Union reclassified Pluto as a 'dwarf planet,' reducing the count from nine. The eight run from Mercury out to Neptune.
5. Which planet is best known for its bright, prominent ring system?
- Uranus
- Jupiter
- Neptune
- Saturn
Saturn's rings are made mostly of countless chunks of ice and rock, ranging from tiny grains to house-sized boulders. Although all four giant planets have rings, Saturn's are by far the brightest and most spectacular. They stretch hundreds of thousands of kilometres wide yet are remarkably thin.
6. What is the name of Earth's only natural satellite?
- Europa
- Phobos
- The Moon
- Titan
The Moon sits about 384,400 kilometres from Earth on average. It is slowly drifting away from us at roughly 3.8 centimetres per year. Its gravitational pull is the main driver of Earth's ocean tides.
7. Which planet is the hottest in the solar system?
- Venus
- Mercury
- Jupiter
- Mars
Venus has a thick carbon-dioxide atmosphere that traps heat in a runaway greenhouse effect. Surface temperatures reach around 465°C, hot enough to melt lead. This makes Venus hotter than Mercury even though it lies farther from the Sun.
8. Whose mathematical predictions guided the 1846 discovery of Neptune?
- Urbain Le Verrier
- Johannes Kepler
- Galileo Galilei
- William Herschel
Le Verrier calculated where an unseen planet must be by studying odd wobbles in Uranus's orbit. On 23 September 1846, astronomer Johann Galle in Berlin found Neptune within a degree of Le Verrier's predicted spot. England's John Couch Adams had reached similar conclusions independently.
9. Which body was reclassified from planet to dwarf planet in 2006?
- Pluto
- Makemake
- Eris
- Ceres
Pluto lost its planet status because it has not 'cleared its neighbourhood' of other objects in the Kuiper Belt. NASA's New Horizons probe flew past it in 2015, revealing a striking heart-shaped plain of nitrogen ice. Pluto has five known moons, the largest being Charon.
10. Which planet is tilted so far on its axis that it essentially rotates on its side?
- Jupiter
- Saturn
- Neptune
- Uranus
Uranus has an axial tilt of about 98 degrees, meaning its poles roughly point toward and away from the Sun. Scientists think a colossal ancient collision knocked it over. This gives Uranus extreme seasons, with each pole spending decades in continuous sunlight or darkness.
11. The main asteroid belt lies between the orbits of which two planets?
- Venus and Earth
- Jupiter and Saturn
- Mars and Jupiter
- Earth and Mars
The main asteroid belt sits between Mars and Jupiter and contains millions of rocky bodies. The largest object there, Ceres, is round enough to be classed as a dwarf planet. Despite countless asteroids, the belt is so vast that the objects are mostly far apart.
12. What is the largest moon of Saturn?
- Rhea
- Titan
- Enceladus
- Europa
Titan is bigger than the planet Mercury and is the only moon known to have a thick atmosphere. It has lakes and rivers of liquid methane and ethane on its frigid surface. In 2005 the Huygens probe landed there, the most distant landing ever made from Earth.
13. What is the largest moon in the entire solar system?
- Ganymede
- Triton
- The Moon
- Titan
Ganymede, one of Jupiter's four large Galilean moons, is bigger than the planet Mercury. It is the only moon known to generate its own magnetic field. Beneath its icy crust, scientists believe it hides a vast subsurface ocean.
14. What is the name of Neptune's largest moon?
- Charon
- Titania
- Triton
- Nereid
Triton is unusual because it orbits Neptune backwards, opposite to the planet's rotation, hinting it was a captured Kuiper Belt object. It is one of the coldest places in the solar system at around -235°C. Voyager 2 spotted geysers erupting nitrogen from its surface.
15. Roughly how long does Neptune take to orbit the Sun once?
- 84 years
- 165 years
- 12 years
- 248 years
Neptune takes about 165 Earth years to complete a single trip around the Sun. Because of this, it finished its first full orbit since its 1846 discovery only in 2011. Neptune also has the fastest winds in the solar system, reaching supersonic speeds.