Mum gets only half of hers, but it's heavenly (4)

I believe the answer is:

mars

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'it's heavenly' is the definition.
I can't judge whether this definition defines the answer.

'mum gets only half of hers' is the wordplay.
'mum' becomes 'ma' (ma can mean mother).
'gets' means one lot of letters go next to another.
'only half of' indicates taking half.
'hers' halved is 'rs'.
'ma'+'rs'='MARS'

'but' is the link.

Can you help me to learn more?

(Other definitions for mars that I've seen before include "classical god" , "Famous Texas mission" , "RS [RED STAR] (not technically)" , "world" , "Fourth planet from the Sun" .)

I've seen this clue in the Evening Standard.

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