This radar image was produced in a 1991 Jet Propulsion Lab (JPL) Goldstone plus NRAO Very Large Array doppler radar experiment.
Mercury does emit radio waves because it is hot, but there are no radio images of the planet.
Scientists have used radio waves to study Mercury by a technique called Radar.
Radio waves were transmitted to Mercury and some reflected off the planet and returned to Earth, where they were detected by radio telescopes.
Red areas show regions of highest reflectivity, that is, where more radio waves reflected back to Earth.
The northern red spot is due to water-ice resting in permanent shade on Mercury's pole.
The origin of the other red (highly reflective) areas remain a mystery.