How many planets are in our solar system (according to the IAU)?
B.8
The IAU classifies eight solar-system bodies as planets; Pluto belongs to the dwarf-planet category.
Planets Trivia
Moons, rings, atmospheres and the eight planets of our solar system.
25 questions
0/25 · 0 correct
Name ____________________ Score ______ / 25
Round 1Solar-system foundations
Which planet is closest to the Sun?
A.Mercury
Mercury orbits inside Venus’s orbit and has the shortest orbital period of the eight planets.
Which planet is known as the Red Planet?
C.Mars
Iron-bearing minerals on Mars’s surface oxidize, producing the reddish appearance associated with rust.
Which planet is the largest in our solar system?
C.Jupiter
Jupiter is the largest planet by both diameter and mass; Saturn is second in size.
On which planet do we live?
D.Earth
Earth is the third planet from the Sun and the only world known to support life.
Which planet is the hottest in our solar system (due to its thick atmosphere)?
B.Venus
Venus’s thick carbon-dioxide atmosphere traps heat, making its surface hotter than Mercury’s despite the distance.
In what order from the Sun is Earth?
C.Third
Mercury and Venus orbit closer to the Sun; Mars is the next planet outward from Earth.
Which planet was reclassified as a dwarf planet in 2006?
A.Pluto
The 2006 definition distinguishes planets from dwarf planets partly by whether they clear their orbital neighborhood.
Which of the eight planets has the smallest diameter?
A.Mercury
Mercury is the smallest planet; Pluto is smaller but is classified as a dwarf planet.
Round 2Moons, rings and planetary systems
Which planet’s bright ring system is conspicuous through a small telescope?
A.Saturn
Other giant planets also have rings, but Saturn’s are especially broad and bright from Earth.
Which planet has no natural moons and lies closest to the Sun?
C.Mercury
Mercury has no moons; Venus also lacks moons, but lies farther from the Sun.
Jupiter's Great Red Spot is what type of feature?
A.A giant storm
The Great Red Spot is an atmospheric storm, not a solid feature on Jupiter’s surface.
How many moons does Mars have?
B.2
Phobos and Deimos are Mars’s two small moons, rather than a single Earth-like large moon.
Which planet’s largest moon is Triton?
A.Neptune
Triton is Neptune’s largest moon and moves in a retrograde orbit around the planet.
Uranus and Neptune are often called what type of planets?
D.Ice giants
Ice giants have compositions that differ from the hydrogen-and-helium-dominated gas giants Jupiter and Saturn.
The asteroid belt is located between which two planets?
D.Mars and Jupiter
Most main-belt asteroids orbit between Mars and Jupiter, although asteroids also exist elsewhere.
Which moon of Saturn is the only moon in the solar system with a dense atmosphere?
A.Titan
Titan’s thick atmosphere is mostly nitrogen; its surface also has lakes and seas of hydrocarbons.
What is the name of the largest moon in our solar system?
A.Ganymede
Ganymede orbits Jupiter and is larger in diameter than Mercury, although it has much less mass.
What are the names of Mars’s two moons?
D.Phobos and Deimos
The names refer to fear and dread in Greek mythology, associated with the war god Ares.
Which planet has the lowest average density, less than that of liquid water?
A.Saturn
Saturn’s low average density reflects its gaseous composition; the familiar floating comparison is hypothetical.
Round 3Rotation, discovery and weather
Which planet rotates on its side (axis tilted about 98 degrees)?
A.Uranus
Uranus’s extreme axial tilt makes its rotation appear sideways relative to its path around the Sun.
Which planet has the shortest day (fastest rotation) in our solar system?
C.Jupiter
Jupiter rotates in roughly ten hours, much faster than Earth’s roughly twenty-four-hour rotation.
Which planet takes longer to rotate once relative to the stars than to orbit the Sun?
D.Venus
Venus’s sidereal rotation takes about 243 Earth days, versus about 225 for its orbit. Its solar day is different.
Irregularities in which planet’s orbit helped astronomers predict Neptune’s position?
D.Uranus
Astronomers used deviations in Uranus’s motion to calculate where another planet might be exerting gravity.
Which planet has the strongest winds in the solar system?
A.Neptune
NASA describes Neptune’s winds as the fastest planetary winds measured in the solar system.