Out of this World Crossword Puzzle

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Across
  1. 3. The star at the center of our Solar System
  2. 5. The theory that explains how the Universe began
  3. 7. A rocky object in space, many of which are found between Mars and Jupiter
  4. 10. A tool placed in space that astronomers can use to collect information
  5. 13. The planet closest to the Sun
  6. 15. The largest planet in our Solar System
  7. 16. A group of planets and other objects that orbit a star
  8. 19. The force that keeps planets orbiting the Sun
  9. 20. The planet we live on
Down
  1. 1. The amount of matter in an object that does not change on another planet
  2. 2. Everything that exists, including all matter, energy, space, and galaxies
  3. 4. A large object in space that revolves around a star
  4. 6. Our home galaxy
  5. 8. The planet famous for its large and visible ring system
  6. 9. A huge collection of stars, gas, and dust held together by gravity
  7. 11. The shape of the Milky Way galaxy
  8. 12. This changes when you travel to a planet with different gravity
  9. 14. A bowl-shaped depression caused when an object from space strikes a surface
  10. 17. An instrument astronomers use to observe distant objects in space
  11. 18. The planet known as the Red Planet