Janos is the name of a planet in a non specified constellation. It is said that it had been inhabited by an oriental looking humanoid civilization, but that it had been destroyed when it was struck by a meteor. The Janosians were able to flee their planet in time, and are now living in their space ships in our solar system.
According to more than one contactee, they have contacted several governments on Earth, hoping to negotiate a deal that would allow them to live in Earth.
Some contactees also mention that the Janosians themselves originally came from Earth, and had emigrated some thousands of years ago.
Other alien 'immigrants' are the Norcans and the Dropas.