Old, old idea by alien to construct a distant Earth? (9)
I believe the answer is:
exoplanet
'construct a distant earth?' is the definition.
I know nothing about this answer so I can't judge whether this works.
'old old idea by alien' is the wordplay.
'old' becomes 'ex' (prefix meaning former or onetime).
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'idea' becomes 'plan' (plan is a kind of idea).
'by' says to put letters next to each other.
'alien' becomes 'et' (extra terrestrial).
'ex'+'o'+'plan'+'et'='EXOPLANET'
'to' acts as a link.
Can you help me to learn more?
(Other definitions for exoplanet that I've seen before include "distant world" , "where no human has ever been" .)