How the solar system formed

Grade 9 Science Worksheet

Circle the best answer.

1. 1.

   Disk with a hot inner zone and a cold outer zone. Sort these by where they formed, nearest the Sun first: an ice giant, a terrestrial planet, a gas giant. By Bo's reading, which order fits?

   • Terrestrial, gas giant, ice giant
   • Ice giant, gas giant, terrestrial
   • Gas giant, terrestrial, ice giant
   • They formed at one distance
2. 2.

   Disk with a line marked where ice could survive. Water ice could survive in the young disk only far enough from the Sun. What did that allow out there, by Esme's reading (NASA)?

   • Rocky planets grew bigger than Earth in the cold outer disk
   • Nothing could form beyond the line
   • Ices and gases gathered into the giant planets
   • The Sun formed there
3. 3.

   NASA says the Sun holds 99.8% of the solar system's mass. What share is left for everything else, by Jun's math?

   • 2%
   • 0.2%
   • 99.8%
   • 20%
4. 4.

   What cleared the leftover gas and dust from the young solar system, by Luz's reading (NASA)?

   • Earth's gravity slowly pulled the gas in
   • A planet exploded and scattered it
   • It is still there between the planets
   • The young Sun's early solar wind
5. 5.

   Planets build up; cloud collapses; solar wind clears the gas; Sun and spinning disk form. Which order matches the formation steps, by Milo's reading?

   • Sun forms, then the cloud collapses around it
   • Gas is cleared first, then the cloud collapses
   • Planets build, cloud collapses, Sun forms, gas is cleared
   • Cloud collapses, Sun and disk form, planets build, gas is cleared

6. Read this first

   Density (NASA Planetary Fact Sheet)

   Planet	Density (kg/m³)
   Earth	5,514
   Saturn	687

7. 6.

   Saturn's density is 687 kg/m³ and Earth's is 5,514 kg/m³ (NASA). What does this fit, by Noah's reading?

   • Both are made of the same things
   • Earth is mostly gas
   • Saturn is mostly gas; Earth is mostly rock and metal
   • Saturn is mostly rock and metal; Earth is mostly gas and ice
8. 7.

   Asteroids are about 4.6 billion years old (NASA). Why do scientists study them to learn about the solar system's start, by Pia's reading?

   • They are leftovers that have changed little since the start
   • They formed just a few thousand years ago
   • They are pieces of a broken planet
   • They are older than the universe
9. 8.

   The universe is about 13.8 billion years old and the solar system about 4.6 billion. For about how long had the universe existed when the solar system formed, by Ren's math?

   • About 18.4 billion years
   • About 9.2 million years
   • About 9.2 billion years
   • It formed at the same moment
10. 9.

    Most planets also spin on their axes in the same direction they orbit. Why does that fit the formation story, by Zee's reading?

    • They kept the spin of the disk they formed in
    • The planets spin because they are cooling
    • The cloud did not spin
    • Each planet was captured separately
11. 10.

    Which statement about the asteroid belt matches NASA, by Ari's reading?

    • The remains of a planet that broke apart
    • Rocks blasted off Mars recently
    • Gas that did not turn into rock, left between Mars and Jupiter
    • Bits that never came together into a planet