Solar System — Answer Key
Part A: Fill in the Blank
Write the missing word or number on each line.
1. The Sun's gravity keeps all eight planets traveling in their orbits.
The Sun's gravity provides the centripetal force that keeps planets in their elliptical orbits.
2. Planets travel around the Sun in oval-shaped paths called elliptical orbits.
Kepler's first law: planetary orbits are ellipses with the Sun at one focus, not perfect circles.
3. The asteroid belt is located between the orbits of Mars and Jupiter.
The main asteroid belt sits between Mars and Jupiter, containing millions of rocky bodies.
4. A comet is an icy body that develops a glowing tail as it approaches the Sun.
Comets are icy nuclei from the outer solar system. Solar heat vaporizes the ice, forming a glowing coma and tail.
5. Pluto was reclassified as a dwarf planet in the year 2006.
In 2006, the IAU defined planets. Pluto doesn't clear its orbital neighborhood, so it became a dwarf planet.
6. Planets closer to the Sun orbit faster than planets farther away.
Kepler's third law: inner planets travel faster. Mercury orbits at ~47 km/s; Neptune at ~5 km/s.
7. A moon is a natural satellite that orbits a planet instead of the Sun.
Natural satellites (moons) orbit planets due to gravity. Earth has one; Jupiter has over 90.
8. The distance from Earth to the Sun is about 93 million miles or one astronomical unit.
1 AU = ~93 million miles (~150 million km). This is the standard unit for solar system distances.
9. The Sun is a star made mostly of hydrogen and helium that produces heat and light.
The Sun is a medium-sized G-type star. Nuclear fusion in its core converts hydrogen to helium and releases energy.
Part B: Matching
Match each item on the left to the correct answer on the right.
1. Match each item to its correct answer.
Asteroid belt
→ Region of rocky debris between Mars and Jupiter
Orbits the Sun but has not cleared its orbital neighborhood
Comet
→ Icy body that develops a bright tail near the Sun
Region of rocky debris between Mars and Jupiter
Dwarf planet
→ Orbits the Sun but has not cleared its orbital neighborhood
Natural satellite that orbits around a planet
Moon
→ Natural satellite that orbits around a planet
Icy body that develops a bright tail near the Sun
Asteroid belt=rocky debris between Mars and Jupiter(idx1); Comet=icy body with tail(idx3); Dwarf planet=hasn't cleared orbital neighborhood(idx0); Moon=natural satellite(idx2)