Jupiter and Saturn emit strongly in radio waves, and astronomers think exoplanets should as well. (Mercury and Mars emit weaker radiation.) Unfortunately, radiation from the solar system’s planets lies in the middle of the commercial radio and TV bands, making the hushed signals difficult to detect.
Mercury, Mars, and Saturn images courtesy NRAO/AUI; Jupiter: ATNF/CSIRO
Yes! Astronomers discovered the first two extrasolar planets using a radio telescope.
So far no extrasolar planets have been directly detected in radio waves. Yet many astronomers think that soon we will detect such signals.
