Final answer:
The passage uses 'investigating' as a synonym for 'exploration' in the line about satellites helping by investigating objects in space.
Step-by-step explanation:
The line in the passage that uses a synonym as a context clue to explain the meaning of the word exploration is: "Some satellites help by investigating faraway objects that may be heading toward Earth." Here, the word 'investigating' serves as a synonym and provides a context clue that helps to clarify the meaning of 'exploration,' which in the context of the passage refers to the systematic study and examination of space and celestial bodies.
In this sentence, the word "exploration" is used to describe the purpose for which satellites have been sent into space. It implies the act of searching, investigating, or studying something in order to gain knowledge or information. Therefore, a synonym for "exploration" in this context could be "investigation" or "study."