NASA has sparked considerable speculation after announcing a Dec. 2 press conference to discuss a "finding that will impact the search for evidence of extraterrestrial life." The rumors grew louder after the scientists slated to speak turned out to be astrobiologists — those who study life in the universe — and others who have looked for living organisms on Mars and the moons of Saturn. Although a spokesperson has dismissed the speculation as "mostly erroneous," curiosity remains high:

This might be "what we've all been waiting for": No wonder rumors are "skyrocketing on the Internet," says Lee Speigel in AOL News. Announcing an "astrobiology" discovery tied to "evidence of extraterrestrial life" is "quite an eye-opening mouthful." People seem hopeful that the news will involve "signs of life, albeit microbial," on Mars, or "potential life" on the Saturn moon Rhea.
"Is ET search heating up? NASA to announce 'astrobiology finding'"

NASA is just teasing the gullible: I can't say for certain that NASA hasn't found alien life, says Phil Plait in Discover. "But it seems really unlikely." A discovery that big wouldn't be telegraphed in a press release. NASA can't say too much because the finding is embargoed, but I wish its press office would smarten up. Now what's sure to be "pretty interesting and scientifically exciting" news will be a letdown because it isn't "actual life on Mars."
"Snowballing speculation over a NASA press conference"

Let the experts speak for themselves: Even if NASA, sadly, has not discovered ET, says Jason Kottke at Kottke.org, the makeup of the panel at the press conference should give us some clues about the "astrobiology finding." My best guess is "that they've discovered arsenic on [the Saturn moon] Titan and maybe even detected chemical evidence of bacteria utilizing it for photosynthesis."
"Has NASA found extraterrestrial life?"