Update 11:45 a.m.: Today's NASA announcement concerned evidence of "possible flowing water during the warmest months of Mars."Read the NASA press release here.
You can watch a narrated presentation of a set of images taken by the Mars Reconnaisance Orbiter that the research team says shows geological changes across seasons, indicating current flowing water on the planet. (Click here for different file formats.)
NASA has announced a news briefing, available to the media at Ames Research Center at Moffett Field, and to everyone else via the web. The space agency says it will announce a "significant new Mars science finding...based on observations from NASA's Mars Reconnaissance Orbiter (MRO), which has been orbiting the Red Planet since 2006."