Mobile communication towers represent a relatively new but growing contributor to the total radio-leakage associated with planet Earth. In new research, astronomers from the University of Mauritius and the University of Manchester investigated the overall power contribution of mobile communication towers to the Earth’s radio leakage budget, as seen from three nearby stellar systems: HD 95735, Barnard’s star, and Alpha Centauri A. They found that the mobile tower leakage is periodic, direction dependent, and could not currently be detected by a nearby alien civilization located within 10 light-years of the Earth, using instrumentation with a sensitivity similar to the Green Bank Telescope.
Saide et al. conclude that any nearby civilization located within 10 light-years of Earth and equipped with a receiving system comparable to the Green Bank Telescope would not detect the Earth’s mobile tower leakage. Image credit: Breakthrough Listen Initiative.
“The goal of search for extraterrestrial intelligence (SETI) is to discover evidence of intelligent life beyond the Earth by looking for so-called techno-signatures — artificially generated signals that are not produced by nature,” said University of Mauritius astronomer Ramiro Saide and colleagues.
“Unfortunately, all signals detected by SETI radio experiments to date have not been attributable to an intelligent civilization, other than our own.”
“In principle, SETI surveys need to be sensitive to a wide range of parameter space — this is due to our ignorance regarding some very basic aspects of the signal we are looking for — including the timing of any transmissions, their location on the sky and their central frequency.”
“In parallel with the search for signs of intelligent life, the topic of exoplanets has had a major impact on the possible incidence of extraterrestrial life in our Galaxy, as we understand more about the conditions on these planetary systems and their potential habitability.”
“Future advances in observing capabilities from space and on the ground have brought up new and intriguing prospects in the search for extraterrestrial life.”
“Most SETI surveys are optimized to detect narrow-band signals from powerful beacons,” the astronomers added.
“It is usually assumed that the detection of fainter, broad-band leakage signals is only relevant to very nearby stellar systems.”
“The possibility of ‘eavesdropping’ on the everyday radio transmissions inadvertently leaking into space from other technical civilizations was first considered by astronomers in 1978.”
“They considered the specific case of our planet Earth and concluded that the most detectable signals were associated with military radar systems and television stations.”
“The nature of the Earth’s radio leakage has changed significantly since the pioneering work was published over 40 years ago,” they said.
“For example, powerful TV transmissions are no longer a major contributor to the Earth’s leakage radiation with the rise of cable TV and the internet. In addition, mobile communication systems were unknown until the 1990s, and they currently represent a new and still growing component of the Earth’s human-generated radio emission.”
“According to a 2022 study, the current number of mobile phone users is 7.26 billion, which suggests in excess of 91.00% of people in the world are cell phone owners.”
“Individual handsets are serviced by a huge network of mobile tower systems that are spread across the landmass of the planet.”
“Although each of these towers generates radio transmissions with relatively low power levels (∼hundreds of watts), the directivity of these antennas and the sheer numbers involved make them a significant component worthy of further study.”
In their new research, Saide and co-authors generated models displaying the radio power that nearby alien civilizations would receive as the Earth rotates and the mobile towers rise and set.
They believe that unless an alien civilization is much more advanced than ours, they would have difficulty detecting the current levels of mobile tower radio leakage from Earth.
However, they suggest that some technical civilizations are likely to have much more sensitive receiving systems than we do, and the detectability of our mobile systems will increase substantially as we move to much more powerful broadband systems.
They are also excited by the fact that their simulations show that the Earth’s mobile radio signature includes a substantial contribution from developing regions, including Africa.
“The results highlight Africa’s success in bypassing the landline stage of development and moving directly into the digital age,” said University of Manchester’s Professor Mike Garrett.
“I’ve heard many colleagues suggest that the Earth has become increasingly radio quiet in recent years — a claim that I always contested — although it’s true we have fewer powerful TV and radio transmitters today, the proliferation of mobile communication systems around the world is profound.”
“While each system represents relatively low radio powers individually, the integrated spectrum of billions of these devices is substantial.”
“Every day we learn more about the characteristics of exoplanets via space missions like Kepler and TESS, with further insights from Webb — I believe that there’s every chance advanced civilizations are out there, and some may be capable of observing the human-made radio leakage coming from planet Earth,” said Dr. Nalini Heeralall-Issur, an astronomer at the University of Mauritius.
The team’s next step is to include powerful civilian and military radars, new digital broadcast systems, Wi-Fi networks, individual mobile handsets and the swarm of satellite constellations now being launched into low Earth orbit, such as Elon Musk’s Starlink system.
“Current estimates suggest we will have more than one hundred thousand satellites in low Earth orbit and beyond before the end of the decade,” Professor Garrett said.
“The Earth is already anomalously bright in the radio part of the spectrum; if the trend continues, we could become readily detectable by any advanced civilization with the right technology.”
The findings appear in the Monthly Notices of the Royal Astronomical Society.
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Ramiro C. Saide et al. 2023. Simulation of the Earth’s radio-leakage from mobile towers as seen from selected nearby stellar systems. MNRAS 522 (2): 2393-2402; doi: 10.1093/mnras/stad378
