Life from space: Not yet (on Earth or Mars)

The controversial Journal of Cosmology has published a paper claiming a fragment of a diatom sampled via balloon from the upper stratosphere (22-27km)  indicates the now-deceased organism was deposited here by a comet.
Really.
A piece of a cell wall from a microscopic algae is not exactly solid, repeatable (so far) evidence for anything this dramatic. While the authors of the paper say all the right things about excluding contamination, the general scientific response is going to be that this must be contamination unless it's repeated - more than once.  Here's the paper. 
Meanwhile, NASA's Curiosity rover is not finding methane on Mars. Any type of life we're familiar with should excrete some methane, but we're still talking about sampling a tiny piece of the planet at surface level.  This is disappointing but not damning. Previous reports of methane on Mars indicated it was trapped in rocks or ice, and releases were occasional events, although whether the methane is of geological or biological in origin is unknown.  The ExoMars Trace Gas Orbiter will arrive in 2016 to hunt for methane from orbit.  (ExoMars is a European Space Agency craft: it was supposed to be a joint project with NASA, but NASA, as is so often the case lately, pulled out as the planetary mission budget shrank.  We're going to reach the point where other spacefaring nations won't even think of doing a major mission jointly with NASA.  Inexcusable.)
The bottom line is that the Red Planet is not - yet - ruled out as a hiding place for past or even current life.  We'd know if we were there, of course...