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?

   • They formed at one distance
   • Ice giant, gas giant, terrestrial
   • Terrestrial, gas giant, ice giant
   • Gas giant, terrestrial, ice giant
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)?

   • Nothing could form beyond the line
   • Ices and gases gathered into the giant planets
   • Rocky planets grew bigger than Earth in the cold outer disk
   • 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?

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

   Disk with a cold outer zone rich in ice and gas. Jupiter has about 318 times Earth's mass (NASA). Why could the giants grow so big, by Kira's reading?

   • They formed long after the Sun had cleared the gas away
   • The cold outer disk had extra ice and gas to gather
   • They swallowed the rocky planets
   • They formed near the hot Sun
5. 5.

   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
   • The young Sun's early solar wind
   • It is still there between the planets

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
   • Saturn is mostly gas; Earth is mostly rock and metal
   • Saturn is mostly rock and metal; Earth is mostly gas and ice
   • Earth is mostly gas
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 older than the universe
   • They formed just a few thousand years ago
   • They are leftovers that have changed little since the start
   • They are pieces of a broken planet
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
   • It formed at the same moment
   • About 9.2 billion years
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?

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

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

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