The Martian atmosphere is so thin that even if the temperature rose above freezing, the ice would change to water vapour.
(The Martian atmosphere; is; so thin that even if the temperature rose above freezing, the ice would change to water vapour) (the ice; would change; to water vapour)
The Martian atmosphere the ice
is would change
so thin that even if the temperature rose above freezing, the ice would change to water vapour
to water vapour