Eavesdropping on radio broadcasts from galactic civilizations with upcoming observatories for redshifted 21 cm radiation

摘要: The question of whether intelligent life exists elsewhere is one the fundamental unknowns about our Universe. Over past decade extra-solar planets have been discovered, providing new urgency for addressing this in these or other planetary systems. Independently perspective, radio observatories cosmology are currently being constructed with goal detecting 21 cm emission from cosmic hydrogen redshift range . frequency band covered by experiments overlaps frequencies used telecommunication on Earth, a regime that was never explored high sensitivity before. For example, low-frequency demonstrator (LFD) Mileura Wide-Field Array (MWA), will cover 8 kHz bins entire 80–300 MHz, which perfectly matched to over civilization emits most its power. We show and (culminating Square Kilometer (SKA)) be able detect broadcast leakage an Earth-like out distance ~101−2.7 pc, within spherical volume containing 10(3−8) × (Ωb/4π)α stars, where α = 1 (or 1.5) radar beam solid angle Ωb remains steady sweeps) across sky. Such signal up as series narrow spectral lines do not coincide known atomic molecular lines. resolution attainable upcoming allow us monitor periodic Doppler shift planet's orbital period around parent star. Determination star mass through observations spectrum could then infer inclination, semi-major axis eccentricity orbit. This, turn, estimate temperature surface assess it can support liquid water we know it.