They're starting on about going to Mars (10)

I believe the answer is:

novitiates

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'they're starting' is the definition.
The definition suggests an adverb but the answer is not.

'on about going to mars' is the wordplay.
'about' says the letters should be written backwards.
'going to' says to put letters next to each other.
'mars' becomes 'vitiates' ('vitiate' can be a synonym of 'mar').
'on' back-to-front is 'no'.
'no'+'vitiates'='NOVITIATES'

Can you help me to learn more?

(Another definition for novitiates that I've seen is " probation periods".)

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