evidence
facts that make you believe something is true

extraterrestrial intelligence
advanced life forms existing beyond our planet

clues
pieces of evidence

analyse
examine

volunteers
people who do something without being paid for it

vital
essential

age-old
long-standing or very old

astronomers
people who study space

citizen
person belonging to a particular country

tantalizing
exciting, making you want more (even if it is not possible)

exists
occurs