Many people claim that they have been abducted by aliens from outer space. They also claim that aliens have performed surgery or research on them or had sexual intercourse with them.
Extraordinary claims require extraordinary proofs, and the burden of proof is on the claimants.
No definitively identified tracks, marks, photographs, pieces of equipment or other artifacts of alien origin exist. Recent research shows that people who are led on and suggestively questioned may imagine events that they will swear really happened. Some research subjects persist in believing in the imaginary events even after the deception has been explained to them. Alien abductions and intrusions are such imaginary events. Research psychologists are beginning to understand the development of such false memories, but can only speculate as to why some people develop false memories about space aliens.