Planet loses temperature on surface (5)
I believe the answer is:
plane
'surface' is the definition.
(I know that plane is a type of surface (mathematics))
'planet loses temperature' is the wordplay.
'loses' is a deletion indicator.
'temperature' becomes 't' (abbreviation).
'planet' with 't' taken away is 'PLANE'.
'on' acts as a link.
(Other definitions for plane that I've seen before include "This flier" , "Aircraft - level surface - carpenter's tool" , "Woodworking tool" , "Smoother" , "Form of transport" .)