Do philosophers believe in aliens? On Wednesday a team of Nasa scientists reported their findings on UFOs for the first time in history. Some say it raises all-new moral dilemmas.
Nasa reveals what it knows about UFOs
Searching for answers: The US Defence Department receives 50 to 100 UFO reports every month. Glossary
Nasa - The National Aeronautics and Space Administration, responsible for the US space programme.
UFOs - Unidentified Flying Objects
Sentient - Able to perceive or feel things.
Colonise - To move to a place and attempt to take it over, at the expense of any existing people.