You can imagine the excitement over the discovery: Microorganisms found in the soil near Columbia Base, Gusev crater, Mars. They sat just below the surface, waiting for the sun to warm up the thin layer of nightly frost to its sublimation point, at which point they would gather it and continue their slow process of metabolizing phosphates and breaking down CO2.
The researchers worked tirelessly to figure out as much as possible about the life forms, including the important bit: whether or not they were indeed alien. The first red flag was that they used DNA, and even had genes that were similar to Earthbound bacteria. Not similar enough, some argued, to have a common ancestor recent enough to have been carried on any manmade probe.
Once the genome was fully sequenced, the dataset was pored over by every biologist on two planets (and one moon). There was a weird non-coding sequence at the end, which puzzled us for a while until some bored kid converted it to ASCII.