The question of whether intelligent life exists elsewhere is one of the fundamental unknowns about our Universe .
Over the past decade \gtrsim 200 extra-solar planets have been discovered , providing new urgency for addressing this question in these or other planetary systems .
Independently of this perspective , new radio observatories for cosmology are currently being constructed with the goal of detecting 21cm emission from cosmic hydrogen in the redshift range 6 \lesssim z \lesssim 15 .
The radio frequency band covered by these experiments overlaps with the range of frequencies used for telecommunication on Earth , a regime that was never explored with high sensitivity before .
For example , the Low-Frequency Demonstrator ( LFD ) of the Mileura Wide-Field Array ( MWA ) , will cover in 8 kHz bins the entire frequency range of 80–300 MHz , which is perfectly matched to the band over which our civilization emits most of its radio power .
We show that this and other low-frequency observatories ( culminating with the Square Kilometer Array [ SKA ] ) will be able to detect radio broadcast leakage from an Earth-like civilization out to a distance of \sim 10 ^ { 1 - 2.7 } pc , within a spherical volume containing 10 ^ { ( 3 - 8 ) } \times ( \Omega _ { b } / 4 \pi ) ^ { \alpha } stars , where \alpha = 1 ( or 1.5 ) for a radar beam of solid angle \Omega _ { b } that remains steady ( or sweeps ) across the sky .
Such a radio signal will show-up as a series of narrow spectral lines that do not coincide with known atomic or molecular lines .
The high spectral resolution attainable with the upcoming observatories will allow to monitor the periodic Doppler shift of the broadcasted lines over the planet ’ s orbital period around the parent star .
Determination of the parent star mass through observations of its spectrum could then be used to infer the inclination , semi-major axis and eccentricity of the planet ’ s orbit .
This , in turn , will allow to estimate the temperature on the planet ’ s surface and to assess whether it can support liquid water or life as we know it .