Crossword Genius

Surface temperature on Mars, say (6)

Ross

I believe the answer is:

planet

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

'mars say' is the definition.
(Mars is an example)

'surface temperature' is the wordplay.
I cannot quite understand how this works, but
'surface' could be 'plane' (I've seen this before) and 'plane' is located in the answer.
'temperature' could be 't' (abbreviation) and 't' is located in the answer.
No letters remain.
This explanation may well be incorrect...

'on' acts as a link.

Can you help me to learn more?

(Other definitions for planet that I've seen before include "Celestial body that revolves around the sun" , "Mercury?" , "body in orbit" , "Neptune, for example" , "Large celestial body" .)

I've seen this clue in The Daily Express and The Mirror.
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