A Martian's vaporised American exploratory craft (5,5)
I believe the answer is:
santa maria
'exploratory craft' is the definition.
(ship used by explorer Christopher Columbus)
'a martian's vaporised american' is the wordplay.
'vaporised' indicates anagramming the letters (the original order is destroyed or vaporised).
'american' becomes 'a' (common abbreviation - e.g. in organisation names).
'a'+'martians'='amartians'
'amartians' is an anagram of 'santamari'.
'santamari'+'a'='SANTA MARIA'
(Other definitions for santa maria that I've seen before include "Historic vessel" , "Columbus' ship" , "Columbus's flagship" , "Brazilian city" , "Flagship of Columbus" .)