Although this strong signal was never positively identified, astronomers have identified in it many attributes characteristic of a more mundane and ultimately terrestrial origin. In this case, a leading possibility is that the signal originates from an unusual modulation between a GPS satellite and an unidentified Earth-based source. Many unusual signals from space remain unidentified. No signal has yet been strong enough or run long enough to be unambiguously identified as originating from an extraterrestrial intelligence.