Solar system trivia

Answer key

1. Mercury. Mercury is the innermost planet. Its short path around the Sun takes about 88 Earth days, the shortest year of any planet.
2. Jupiter. Jupiter is the largest planet in both size and mass. It is a gas giant, with a diameter about eleven times Earth’s.
3. A star. The Sun is a star, producing energy through nuclear fusion in its core.
4. Mars. Iron minerals on the surface oxidize, giving Mars its reddish appearance.
5. Saturn. Saturn has bright, extensive rings made mostly of pieces of ice, with rock and dust.
6. Venus. Venus has a thick atmosphere that traps heat through an extreme greenhouse effect.
7. Mars and Jupiter. Most main-belt asteroids orbit between Mars and Jupiter.
8. Uranus. Uranus’s axis is tilted about 98 degrees, so the planet spins almost on its side. This gives it especially extreme seasons.
9. Eight. There are eight planets. Pluto is classified as a dwarf planet.
10. Neptune. Neptune is the outermost of the eight planets. Pluto lies in the Kuiper Belt and is classified as a dwarf planet.
11. Mercury. Mercury is the smallest planet; it is only a little wider than the Moon.
12. Venus. Venus has a diameter only slightly smaller than Earth’s.
13. Mercury and Venus. Mercury and Venus have no natural moons. A nearby asteroid that follows a similar path around the Sun is not necessarily a moon orbiting the planet.
14. Phobos and Deimos. Phobos and Deimos are small, irregularly shaped moons. Phobos is the larger one and orbits closer to Mars.
15. A giant storm. The Great Red Spot is a long-lived storm in Jupiter’s atmosphere.
16. Ganymede. Ganymede is even larger in diameter than Mercury.
17. Titan. Titan’s atmosphere is mostly nitrogen. Its surface lakes and seas contain liquid methane and ethane, rather than the liquid water in Earth’s lakes.
18. Triton. Triton’s orbit is retrograde: it travels opposite to Neptune’s rotation. This unusual motion is evidence that Neptune may have captured it.
19. Ceres. Ceres is the largest object in the main asteroid belt.
20. The Kuiper Belt. The Kuiper Belt contains many icy bodies beyond Neptune.
21. Gravity. Gravity continually bends a moving planet’s path toward the Sun. The planet’s forward motion keeps it orbiting instead of falling straight inward.
22. An orbit. An orbit is the path one body follows around another under gravity.
23. One year. One orbit is one year, roughly 365.25 days. The extra fraction of a day is why our calendar needs leap-day adjustments.
24. Earth rotating on its axis. Earth’s rotation brings different places into sunlight and then darkness.
25. Its tilted axis as it orbits the Sun. Earth’s tilt changes the angle and duration of sunlight over the year.
26. It reflects sunlight. Moonlight is reflected sunlight. The phases change because we see different amounts of the Moon’s sunlit half as it orbits Earth.
27. The Moon. The Moon passes between Earth and the Sun, blocking some or all of the Sun from a small area on Earth.
28. Earth. Earth lies between the Sun and Moon, and the Moon moves into Earth’s shadow. This arrangement occurs only at full Moon.
29. A meteorite. A meteoroid is the object in space, a meteor is the bright atmospheric streak, and a meteorite is material that survives to reach the ground.
30. A meteoroid entering the atmosphere. The visible atmospheric streak is called a meteor.
31. Ice, dust, and rock. Comets contain frozen materials mixed with dust and rocky material.
32. Away from the Sun. The solar wind carries ionized gas away from the Sun.
33. A stream of charged particles from the Sun. The Sun continuously releases charged particles into space.
34. The photosphere. The photosphere is the layer from which most visible sunlight escapes. It is called a surface even though the Sun has no solid ground.
35. The corona. The faint corona extends far above the Sun’s visible surface.
36. Nuclear fusion. Hydrogen nuclei combine to form helium, releasing energy.
37. Eight minutes. Sunlight takes about eight minutes and twenty seconds to cross the average Sun–Earth distance. The delay changes slightly as Earth moves along its orbit.
38. Earth’s average distance from the Sun. One astronomical unit is about 150 million kilometers, approximately the average Sun–Earth distance. It is a convenient scale for planetary orbits.
39. Mercury. Mercury completes an orbit in about 88 Earth days.
40. Neptune. Neptune needs about 165 Earth years to orbit the Sun.
41. Jupiter. Jupiter spins once in about 9.9 hours, giving it the shortest rotation period of the eight planets. A rotation is distinct from an orbit.
42. Uranus and Neptune. Uranus and Neptune are ice giants. The name refers to their water-, ammonia-, and methane-rich interiors; it does not mean they are solid balls of ice.
43. Mars. Olympus Mons is an enormous shield volcano on Mars.
44. Mars. Valles Marineris stretches across thousands of kilometers of Mars.
45. New Horizons. New Horizons flew past Pluto on July 14, 2015. It sent back the first close views of the dwarf planet and its moons.
46. Apollo 11. Apollo 11 landed Neil Armstrong and Buzz Aldrin in July 1969. Michael Collins remained in lunar orbit in the command module.
47. Cassini. Cassini studied Saturn, its rings, and its moons before its mission ended.
48. Juno. Juno was sent to investigate Jupiter’s interior, atmosphere, and magnetic field.
49. Charon. Charon is about half Pluto’s diameter. That unusually large relative size makes Pluto and Charon a distinctive pair.
50. Earth. Earth is the only world with confirmed life. Evidence that another world once had water or could be habitable is not a detection of life.