Aliens!

12345678910111213141516171819202122232425262728293031
Across
  1. 4. someone who studies the physics of space
  2. 6. a spacecraft orbiting a planet
  3. 7. the universe is ______________ of years old
  4. 10. a 1979 film starring Sigourney Weaver
  5. 13. someone not from Earth
  6. 16. a way of relating space and time
  7. 19. how the universe began
  8. 21. a huge collection of gas, dust, and billions of stars and their solar systems, all held together by gravity
  9. 22. someone from Mars, may or may not be named Marvin
  10. 24. unidentified flying object
  11. 25. a disk-shaped UFO is called a flying _______
  12. 26. a town in New Mexico infamous for alleged alien activity
  13. 27. concept that proposes a barrier to the development of life that makes it unlikely to find extraterrestrial civilizations
  14. 28. a hypothetical structure that connects distant points in spacetime
  15. 31. the magnetic field surrounding and protecting Earth
Down
  1. 1. the mathematical formula for the probability of finding life
  2. 2. the gases that shield and protect Earth
  3. 3. the book "War of the _____________" was broadcast on the radio and made Americans think aliens were attacking
  4. 5. a human exploring space
  5. 8. a ship...for going into space
  6. 9. the contradiction between the high likelihood for extraterrestrial intelligence and the lack of evidence for it
  7. 11. a planet outside of our solar system
  8. 12. the area around a star where liquid water can exist on the surface of a planet is called the __________________ Zone
  9. 14. a rare and extreme black hole
  10. 15. how far light travels in 1 year
  11. 17. someone who studies space
  12. 18. someone from Earth
  13. 20. a classification scale for hypothetical alien civilizations
  14. 23. a baby star
  15. 29. the planet we humans live on
  16. 30. the stereotypical color of a fictional alien