Extraterrestrial experiment? (5)

I believe the answer is:

trial

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'experiment?' is the definition.
(trial is a kind of experiment)

'extraterrestrial' is the wordplay.
'TRIAL' is hidden within the letters.
But, I'm unsure how this is indicated.

Can you help me to learn more?

(Other definitions for trial that I've seen before include "Test of suitability" , "Proceedings to determine guilt or innocence" , "Pilot" , "Hearing - difficulty" , "Suffering - litigation" .)

I've seen this clue in the Evening Standard.

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