There's something going on beneath the surface of Jupiter's icy moon Europa. But what? NASA teased a "surprising" announcement for Monday, based on Hubble Space Telescope images of the celestial body, which many experts believe could contain a subsurface ocean, even possibly some form of life. The US space agency has already proclaimed that Europa has "strong evidence for an ocean of liquid water beneath its crust and which could host conditions favorable for life." At Monday's announcement, "astronomers will present results from a unique Europa observing campaign that resulted in surprising evidence of activity that may be related to the presence of a subsurface ocean," it said in a statement. The announcement will be made at a news conference at 2 pm (1800 GMT) Monday featuring Paul Hertz, NASA's director of astrophysics, and William Sparks, an astronomer with the Space Telescope Science Institute in Baltimore.