Crass lies about aliens turning back from Mars (9)
I believe the answer is:
tasteless
'crass' is the definition.
(I've seen this in another clue)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for tasteless that I've seen before include "Unseemly" , "Lacking flavour or ability to appreciate the beautiful" , "improper" , "Insipid - vulgar" , "Vapid" .)