The Solar System — Practice · Grade 9 Science

Chapter: Earth, Moon & Solar System

What this practice covers

By the end of The Solar System you should be able to:

11 questions, multiple choice, numeric and written answer, each with a worked explanation.

Vocabulary used: astronomical unit (AU), terrestrial planet, gas giant, asteroid.

Problem 1

Which planet is closest to the Sun?
  1. Mercury
  2. Venus
  3. Earth
  4. Mars
Answer and explanation

Mercury

Mercury is the innermost planet, orbiting closest to the Sun.

Problem 2

About what percent of the solar system's total mass is contained in the Sun?
Answer and explanation

99.8 %

The Sun holds about 99.8% of all the mass in the solar system.

Problem 3

Jupiter and Saturn are best classified as…
  1. Terrestrial planets
  2. Gas giants
  3. Ice giants
  4. Dwarf planets
Answer and explanation

Gas giants

Jupiter and Saturn are huge, made mostly of hydrogen and helium gas, with rings and many moons — that makes them gas giants.

Problem 4

Uranus and Neptune are made mostly of icy materials (water, ammonia, methane) plus hydrogen and helium gas. What group are they in?
  1. Terrestrial planets
  2. Gas giants
  3. Ice giants
  4. Asteroids
Answer and explanation

Ice giants

Uranus and Neptune's icy composition places them in their own group: the ice giants.

Problem 5

What is the correct order as a small rocky object from space enters the atmosphere and lands?
  1. Meteoroid → meteor → meteorite
  2. Meteor → meteoroid → meteorite
  3. Meteorite → meteor → meteoroid
  4. Meteoroid → meteorite → meteor
Answer and explanation

Meteoroid → meteor → meteorite

It's a meteoroid while in space, becomes a meteor (a streak of light) while burning up in the atmosphere, and any piece that survives to hit the ground is a meteorite.

Problem 6

Explain why astronomers use astronomical units (AU) instead of miles or kilometers to describe distances in the solar system.
Answer and explanation

AU keeps the numbers small and easy to compare. Instead of writing hundreds of millions or billions of miles or kilometers, astronomers can just say a planet is, for example, 5 AU from the Sun, using Earth's own distance from the Sun as a simple, familiar yardstick.

Problem 7

A model places Earth 1 m from the Sun. At the same distance scale, a planet at 5 AU is how far away? Explain the reasoning in your own words.
Answer and explanation

5 m from the model Sun; planet-size scale may still differ.

One AU corresponds to 1 m in this model.

Multiply 5 AU by 1 m/AU.

Response criteria

  • Use the stated conditions.
  • Show the evidence or calculation.
  • Explain the conclusion and any stated limitation.

Problem 8

Why is an astronomical unit useful for planetary distances? Show the reasoning, not just the conclusion.
Hints

Larger radius alone does not determine greater mean density.

Answer and explanation

It provides a convenient scale based on Earth's average Sun distance, avoiding very large kilometer values.

Problem 9

Must a moon be smaller than every planet?
Hints

State what the supplied observations or conditions establish, and separate that from any assumption.

Answer and explanation

No. Categories concern orbital and physical criteria; some large moons exceed some planets in diameter.

Problem 10

Object class and observed activity are different questionsObject class and observed activity are different questionsSunPlanet and moonA comet tail responds to solar effects, not only the travel directionSelected motionTail away from Sun
Original qualitative comet/planet/moon scene with exaggerated body sizes and one selected ion-tail direction. It is not a real encounter image or simultaneous orbital-position map. The caption distinguishes the ion-tail example from possible curved dust-tail geometry.
Interpret the supplied visual model. Why can a comet tail fail to point behind its direction of travel?
Answer and explanation

Solar wind/radiation affect released material, so tail direction depends on the Sun and material type as well as the orbit. An ion tail points broadly away from the Sun.

The blue motion arrow and green away-from-Sun tail arrow point in different directions. The tail is one selected ion-tail direction, not a universal dust-tail shape.

Solar wind/radiation affect released material, so tail direction depends on the Sun and material type as well as the orbit. An ion tail points broadly away from the Sun.

Response criteria

  • Read the labeled quantities, reference frame or objects correctly.
  • Explain the relation between the visual evidence and the mechanism.
  • Keep the drawing’s stated assumptions and limits in the conclusion.

Problem 11

A Solar System distance model places a body at a = 10 AU. Convert that scale to kilometres using 1 AU ≈ 150 million km. Explain why the distance and an image of a water-related feature do not alone establish its size or life.
Answer and explanation

The scale is about 1.5 billion km. It is an orbital distance, not a diameter. A water-related surface interpretation concerns geological conditions and does not alone prove organisms or all habitability requirements.

The scale is about 1.5 billion km. It is an orbital distance, not a diameter. A water-related surface interpretation concerns geological conditions and does not alone prove organisms or all habitability requirements.

Response criteria

  • Use the stated measurements or conditions, with correct units.
  • Connect the result to the physical mechanism or evidence relationship.
  • Identify the assumption, model limit or further evidence requested.

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