A mysterious visitor

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Across
  1. 2. having little extent from one surface to the opposite (4 letters)
  2. 4. To travel through an area to learn about it (7 letters)
  3. 5. Struck with a force (7 letters)
  4. 6. Moving past something (7 letters)
  5. 8. A possibility not 100% but 50%(5 letters)
  6. 9. Risky or hazardous (9 letters)
Down
  1. 1. Difficult to understand or explain (10 letters)
  2. 3. Tools and machines created using scientific knowledge (10 letters)
  3. 7. The rate at which someone or something moves (5 letters)