Also found in: Dictionary, Thesaurus, Acronyms, Encyclopedia, Wikipedia.

be (living) on another planet

slang To be oblivious to one's surroundings or act strangely. I have no idea what the professor said during today's lecture because I was on another planet the whole time. The millionaire investor always says something wacky in the board meetings—it's like he's on living another planet.
See also: another, on, planet

What planet is (someone) on?

What are you thinking? That is an absurd or stupid thing to think or do. (Implies that someone would only do or think that if they were an alien from another planet.) A: "I think they should just do away with taxes altogether!" B: "What planet are you on? Taxes pay for hospitals, roads, our military—literally everything on which our society is built." What planet is he on? He could get someone killed driving that speed along a residential road!
See also: planet, what

what planet is someone on?

COMMON You can say what planet is someone on? to show that you think someone has crazy ideas or does not know about something that most people know about. What planet are these people on? Do they not read their own headlines? Note: This expression is often varied. For example, you can ask what planet does someone live on? or what planet does someone come from?. He thinks hospitals can make major cuts to their budgets. What planet does he live on? Note: You can also say that someone is on another planet. She was just on another planet, I think. She didn't seem to understand that we are ordinary people.
See also: planet, someone, what

what planet are you on?

used to indicate that someone is out of touch with reality. British informal
See also: planet, what

be on another ˈplanet


what ˈplanet is somebody on?

(spoken, humorous) used to suggest that somebody’s ideas are not realistic or practical: He can’t really think we’re going to finish the job today, can he? What planet is he on?
See also: another, on, planet
References in periodicals archive ?
now contends that when it comes to planet formation, two stars are at least as good as one and, in some cases, even better.
A planet among a trio of stars isn't merely a novelty.
With an orbit whose radius is only one-tenth that of Mercury's path around the sun, the planet has a searing surface temperature of 1,500 kelvins, and it whips around the sunlike star HD 149026 in just 2.
These reservoirs of dust are generated when the tugs of planets disturb the orderly orbits of asteroids, comets, and other detritus left over from the planet-making era.
But given the recent advances in planet detection, the discovery bodes well for finding habitable planets, comments theorist Doug Lin of the University of California, Santa Cruz.
Other than shedding light on the formation and abundance of terrestrial planets throughout our galaxy, the presence of hot Earths could answer a burning question among planet hunters: How do giant, Jupiterlike planets form?
Brown had found an outer-solar system object heavier than Pluto, so it seemed reasonable to call the object the tenth planet.