Crossword Genius

NASA's possible question to lost space probe — seriously? (4,6,3,3,2)

Ross

I believe the answer is:

what planet are you on

I'm a little stuck... Click here to teach me more about this clue!

'seriously?' is the definition.
(are you serious?!)

'nasa's possible question to lost space probe' is the wordplay.
I cannot really understand how this works, but
'possible' could be 'on' ('not on' can mean unacceptable or not possible) and 'on' is located in the answer.
'question' could be 'what' (what is a question word) and 'what' is located in the answer.
'lost' could be 'l' (abbreviation in sporting league tables) and 'l' is located in the answer.
This explanation may well be incorrect...

Can you help me to learn more?

I've seen this clue in The Guardian.
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