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Across 3. Discovered by William Herschel, the first to be discovered since ancient times 4. A type of planet without a solid surface 6. The biggest planet in the Solar System 7. Called "Earth's Twin" because it is similar in size 9. The only planet known to have life 11. Only planet that is less dense than water 12. Has two moons called Phobos and Deimos 14. Has the greatest range of temperatures in the Solar System 15. Called the Red Planet because of its red, rusty soil 16. Discovered with mathematical calculations before it was seen 21. Difficult to see because it is so small and close to the Sun 22. Has a day that is longer than its year 23. The brightest planet

Down 1. Has a tilt similar to Earth, so it also has 4 seasons 2. Planet with the most moons, including the 4 Galilean Moons 5. A type of planet that has a solid, rocky surface 6. Has a Great Red Spot that is bigger than 3 Earths 8. Planet is tipped on its side so it spins from top to bottom 10. Only planet known to have liquid water 13. Has the most extensive ring system in the Solar System 14. This planet, along with Venus, are the only two planets without moons 17. Only planet that spins on its axis backwards 18. Mercury, Venus, Earth and Mars are all considered this type of planet 19. The hottest planet because its thick atmosphere traps in heat 20. Jupiter, Saturn, Uranus, and Neptune are all considered this type of planet