Mobile signals could reveal our presence to aliens, finds study

While TV broadcast over radio signals has drastically reduced, a new source has emerged, the mobile phone.

How mobile phones broadcast our presence

As per recent estimates, there are over 10 billion mobile phone connections across the world. These require a large number of mobile towers which individually may not be very powerful but cumulatively add up to be a very strong signal.

To figure out if the signal was powerful enough to be detected by a civilization on a nearby star, researchers at the University of Manchester and the University of Mauritius developed a computer model.

The model was based on publicly available information about mobile phone usage and their distribution in different geographies of the globe. The team chose three stars, located within 10 light years from Earth, and assumed that a radio telescope equivalent to the Green Bank Telescope in West Virginia was orbiting each of the stars and detecting radio signals.

As per their computer model, mobile phone networks leak a peak power of about four gigawatts, while mobile phones themselves cumulatively leak lesser. Nevertheless, this output is not sufficient for a Green Bank-like radio telescope to pick a signal from Earth.

However, if a more advanced telescope was built or the signal output from Earth increased, which is likely in the coming years, that would be sufficient to bring the planet on the alien civilization's radar, the researchers said.

Interestingly, since mobile signals are transmitted parallel to the horizon and are distributed unevenly across the globe, they could be used to draw maps of their location and possibly even guess the distribution of landmass and waterbodies from afar. The research findings were published in the journal Monthly Notices of the Royal Astronomical Society.

For their next phase of research, the team wants to compute the impact of other sources such as WiFi networks, new digital broadcast systems, and satellite constellations such as Starlink.

Study abstract:

Mobile communication towers represent a relatively new but growing contributor to the total radio-leakage associated with planet Earth. We investigate the overall power contribution of mobile communication towers to the Earth’s radio leakage budget, as seen from a selection of different nearby stellar systems. We created a model of this leakage using publicly available data of mobile tower locations. The model grids the surface of the planet into small, computationally manageable regions, assuming a simple integrated transmission pattern for the mobile antennas. In this model, these mobile tower regions rise and set as the Earth rotates. In this way, a dynamic power spectrum of the Earth was determined, summed over all cellular frequency bands. We calculated this dynamic power spectrum from three different viewing points – HD 95735, Barnard’s star, and Alpha Centauri A. Our preliminary results demonstrate that the peak power leaking into space from mobile towers is ∼4GW. This is associated with Long Term Evolution (LTE) mobile tower technology emanating from the East Coast of China as viewed from HD 95735. We demonstrate that the mobile tower leakage is periodic, direction dependent, and could not currently be detected by a nearby civilization located within 10 light-years of the Earth, using instrumentation with a sensitivity similar to the Green Bank Telescope. We plan to extend our model to include more powerful 5G mobile systems, radar installations, ground based up-links (including the Deep Space Network), and various types of satellite services, including low-Earth orbit constellations, such as Starlink and OneWeb.