Curiosity practically rules out life on Mars.
http://www.extremetech.com/extreme/139973-curiositys-latest-discovery-probably-rules-out-life-on-mars
"Far, far away, on the diminutive, 4000-mile-wide Red Planet, Mars Science Laboratory (MSL) Curiosity has unfortunately found no methane in the Martian atmosphere. This puts a fairly large dent in the likelihood of there being life on Mars."