On Mars, perhaps, one could refuse to be held to it (6)
I believe the answer is:
ransom
'one could refuse to be held to it' is the definition.
I can't judge whether this defines the answer.
'on mars perhaps' is the wordplay.
'perhaps' is an anagram indicator.
'on'+'mars'='onmars'
'onmars' is an anagram of 'RANSOM'.
Can you help me to learn more?
(Other definitions for ransom that I've seen before include "Rescue" , "Fee for kidnap release" , "Payment for the release of someone" , "demand an extortionate price" , "Means to release prisoner" .)