Yes, NASA may have killed space aliens. No, they didn't run over E.T. with a shuttle (although I'd pay to see that). Instead, as reported on a number of public news websites yesterday, we are talking about microbes on Mars:
Back in 1976 and '77, the Viking Mars probes landed and studied samples of soil looking for earth-like microbes. Unfortunately, NASA didn't know as much about the environment on Mars as they do now, or Earth for that matter, or about microbes that can survive in such conditions. They were looking for the sort of microbes you find in the soil just outside your front door (i.e. bacteria that live at standard pH and like water at a comfortable 72° F). To look for them, Viking basically sprayed room-temperature water into the soil to rehydrate "normal" bacteria and then test. But it turns out that any living bacteria living there would have evolved to survive the -68°F temperatures, likely by incorporating hydrogen peroxide into them, which boils at room temperature. Thus, if there were any bacteria alive, they would have boiled and been dead before they would be analyzed.
If you think bacteria couldn't possibly live in conditions like that on Mars, you'd be wrong. Called Archaebacteria or Archaea, these "extremophiles" have been found in superheated deep-sea vents and frozen-over Antarctic lakes, in nuclear waste, in high salt concentrations, in the absence of oxygen, and in super-acidic rivers. Here's a link to more info. I've even heard of an acid-loving bacterium that was found exclusively in a latrine outside an English castle where people had urinated for centuries. If they can live in these environments, why not on Mars?
Of course, how do you detect something too small to see and radically different from earthlings (like having hydrogen peroxide in it)? And if detecting them is so difficult, how about determining if they have any degree of intelligence? For all we know the relatives of those tiny bacteria we killed in '77 are plotting their revenge against us for boiling them alive. I think the next time we squirt water onto Martians we'd better play some soothing music and have bubblebath ready. We could call it the "Viking Spa Treatment." That way, just in case they are sentient and we still boiled them alive, we could claim we were trying to relax their little bacterial bodies from the worries of living on a barren, frigid rock of a planet.
So watch out, E.T.! We're coming for you with our super-soakers!