Earth is a human colony. Nasa keeping this secret as we have had alien wars before and lost.

Earth is a human colony and there could be more humans out there. Nasa is keeping all this information away from the public as they are studying ways to avoid conflict with aliens as we have had wars before with them and lost (losing our technology within these wars). They do not want people to know aliens exist and humans have travelled to different planets before until they deem its safe to disclose this information.